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1
Wang, Lei, Bohang Liu, Hanzhi Yang, Yintong Guo, Jing Li e Hejuan Liu. "Experimental Study on the Compressive and Shear Mechanical Properties of Cement–Formation Interface Considering Surface Roughness and Drilling Mud Contamination". Energies 15, n. 17 (5 settembre 2022): 6472. http://dx.doi.org/10.3390/en15176472.
Abstract (sommario):
In a casing-cement sheath-formation system, the cement–formation interface is usually weakly cemented for the residual of drilling mud, in which a leakage path would easily form, threatening the safe operation of underground energy exploitation and storage. To evaluate the compressive and shear mechanical behavior of the cement–formation interface, cement–rock composite cylindrical specimens were prepared. Uniaxial and triaxial compression and direct shear tests were implemented. The flushing efficiency of the rock surface, compressive strength, interface incompatible deformation, parameters of shear strength, and morphology of shear failure surface were acquired and analyzed. Results show that the flushing efficiency of shale surface decreases from 76.7% to 64.2% with the surface roughness increasing from 0 to 2 mm. The flushing efficiency of sandstone is only 44.7%, remarkably lower than that of shale. With the stress condition transforming from uniaxial to triaxial compression, the feature of the stress–strain curves changes from elastic-brittle to elastoplastic, and the compressive strength increases from 20.6~60.1 MPa to 110~120 MPa. The cement part presents noteworthy plastic deformation and several micro shear fractures develop. There is incompatible deformation between cement and rock, which induces interface debonding for almost all the composite specimens. The internal friction angle and cohesive strength both decrease with the increase in pollution degree of drilling mud, and increase with the rise in surface roughness. The shear facture surface is not exactly the rock–cement interface, but usually manifests as a shear zone, in which the rock, cement, and interface all contribute to the final shear failure. The above findings would be valuable for the revealing of cement–formation interface failure mechanism.
2
Tian, Hui, Huajie Liu, Yuhuan Bu, Zihan Chen e Shenglai Guo. "Effect of Composite Interface Enhancer on the Cementation Strength of Shale Formation–Cement Ring Interface". Processes 12, n. 2 (17 febbraio 2024): 405. http://dx.doi.org/10.3390/pr12020405.
Abstract (sommario):
The cement strength between the cement and the formation is a key factor in determining the cementation sealing capacity. In the shale formation, due to the organic matter content, the cementing quality between the formation and the cement ring is poor, which affects the quality of cementing. It is easy to cause problems such as annulus pressure. To improve the quality of cementing, this paper investigates the effect of amino silane coupling agents, vinyl silane coupling agents and aluminium–zirconate coupling agents on the interface cementation of rock and cement under different conditions. Meanwhile, the effects of different coupling agent compounding on improving the cementation interface cement strength under different temperature and concentration conditions were investigated. This led to the development of a composite interface enhancer. The composite interface enhancer can improve the bond strength between cement and rock by 189.22%. A preflush fluid system was developed to effectively improve the cementation strength of mud shale formations, and its performance was evaluated. The density of the preflush fluid system is 1.15 g·cm−3, and it has good rheology, settlement stability, and filtration loss. In addition, it improves the cementing interface cementing strength between the cement and shale formation.
3
Jenni, Andreas, e Urs Mäder. "Reactive Transport Simulation of Low-pH Cement Interacting with Opalinus Clay Using a Dual Porosity Electrostatic Model". Minerals 11, n. 7 (22 giugno 2021): 664. http://dx.doi.org/10.3390/min11070664.
Abstract (sommario):
Strong chemical gradients between clay and concrete porewater lead to diffusive transport across the interface and subsequent mineral reactions in both materials. These reactions may influence clay properties such as swelling behaviour, permeability or radionuclide retention, which are relevant for the safety of a radioactive waste repository. Different cement types lead to different interactions with Opalinus Clay (OPA), which must be understood to choose the most suitable material. The consideration of anion-depleted porosity due to electrostatic repulsion in clay modelling substantially influences overall diffusive transport and pore clogging at interfaces. The identical dual porosity model approach previously used to predict interaction between Portland cement and OPA is now applied to low-alkali cement—OPA interaction. The predictions are compared with corresponding samples from the cement-clay interaction (CI) experiment in the Mont Terri underground rock laboratory (Switzerland). Predicted decalcification of the cement at the interface (depletion of C–S–H and absence of ettringite within 1 mm from the interface), the Mg enrichment in clay and cement close to the interface (neoformation of up to 17 vol% Mg hydroxides in concrete, and up to 6 vol% in OPA within 0.6 mm at the interface), and the slightly increased S content in the cement 3–4 mm away from the interface qualitatively match the sample characterisation. Simulations of Portland cement—OPA interaction indicate a weaker chemical disturbance over a larger distance compared with low-pH cement—OPA. In the latter case, local changes in porosity are stronger and lead to predicted pore clogging.
4
Ballivy, Gérard, Brahim Benmokrane e Pierre Claude Aitcin. "Rôle du scellement dans les ancrages actifs scellés dans le rocher". Canadian Geotechnical Journal 23, n. 4 (1 novembre 1986): 481–89. http://dx.doi.org/10.1139/t86-078.
Abstract (sommario):
The dimensioning of anchor bars grouted in rock takes into account the mechanical properties of the three components steel, grout, and rock. The allowable bond strength at the rock–grout interface recommended by different national codes is generally selected according to the type of rocks and assuming an ordinary cement grout. In the present approach, the influence of the type of grout on the pull-out strength of anchor bars in a sound rock mass with mechanical properties equal or higher than the grout is considered. This experimental study shows that certain cement grouts can develop pull-out strength clearly higher than those obtained with epoxy grouts for example. Key words: rock mass, grouted anchors, cement grouts, epoxy grouts, pull-out test, creep test. [Journal translation]
5
Holý, Ondřej. "Evaluation of Many Load Tests of Passive Rock Bolts in the Czech Republic". GeoScience Engineering 63, n. 1 (1 marzo 2017): 1–7. http://dx.doi.org/10.1515/gse-2017-0001.
Abstract (sommario):
Abstract Within the research project “FR-TI4/329 Research and development - creating an application system for the design and analysis of soil and rock anchors including the development of monitoring elements”, an extensive stage of field load tests of rock bolts was carried out. The tests were conducted at 14 locations with varied rock composition. Before the initial tests, a loading stand was designed and constructed. A total of 201 pieces of tensile tests of bolts having lengths from 0.5 up to 2.5 m, a diameter of 22-32 mm, were performed. These were fully threaded rods, self-drilling rods, and fiberglass rods. The bolts were clamped into the cement and resin. The loading tests were always performed until material failure of bolts or shear stress failure at the interface cement-rock. At each location, basic geotechnical survey was carried out in the form of core drilling in a length of 3.0 metres with the assessment of the rock mass in situ, and laboratory testing of rock mechanics. Upon the completion of testing protocols, rock mass properties analysis was performed focusing on the evaluation of shear friction at the grouting-rock interface.
6
Bathija, Arpita P., e Peter J. Boul. "An Integrated Approach to Study Cement-to-Formation Bonding". Energies 15, n. 16 (17 agosto 2022): 5949. http://dx.doi.org/10.3390/en15165949.
Abstract (sommario):
It is crucial to assess the bond strength of the cement–formation interface while developing novel cements for efficient zonal isolation. An integrated method is presented to investigate the failure mechanism in cement and formation rock under downhole reservoir temperature and pressure conditions using a triaxial experimental setup. The acoustic emission count, strain, and velocity data aid in inferring the fracture process that led to the failure of a specimen. Although most specimens investigated exhibit the three dominant events of compaction, multi-cracking, and sliding, there are variations in the basic structure of each specimen. Furthermore, the insight obtained about the internal structure of the specimen points to its strength and damage tolerance, both of which are vital requirements for bonding. This method can distinguish between a standard cement and modified cement very effectively and help in pairing the appropriate cement formulation for a formation rock.
7
Shishkanova, V. N., M. V. Ivanko e Andrey Yu Kozlov. "Cullet-Filled Concrete". Materials Science Forum 992 (maggio 2020): 73–78. http://dx.doi.org/10.4028/www.scientific.net/msf.992.73.
Abstract (sommario):
The paper considers how cullet of different particle-size distribution affects the concrete strength. Experiments have proven that large-particle cullet (1.25 cm or larger) could be used as an aggregate; the concrete strength will be on par with those of ordinary natural/crushed sand concrete. The paper proves the feasibility of injecting highly dispersed silica fume in combination with effective polycarboxylate-based superplasticizers in cullet-based concrete mixtures. Highly dispersed silica fume will positively affect the strength characteristics of concrete, as silica fume in cement rock reacts with Са (ОН)2, which is released upon the hydration of the clinker minerals С3S and С2S; the reaction produces very strong compounds. Concretes containing up to 30% silica fume in combination with a superplasticizer will feature very high early strength. Use of strong aggregates with a 30% cullet content can produce strong concretes; after steamed, a concrete containing silica fume and polycarboxylate-based superplasticizer will reach 90% of the graded strength. Cement-rock microstructure studies show that the polymer component of the STACHEMENT 2280 superplasticizer will gradually transcend from the glass grains to the cement rock. The interface between the polymer-coated glass grains and the cement rock is blurred and barely present. This strengthens the glass-rock adhesion and improves the concrete strength. This is why cullet is recommended for use in the production of curb stones.
8
Rezzoug, A., A. Alexis e P. Thomas. "Écoulement à surface libre dans un massif de sol soumis à la marée : comparaison théorie-expérimentation". Canadian Geotechnical Journal 36, n. 1 (8 agosto 1999): 13–20. http://dx.doi.org/10.1139/t98-078.
Abstract (sommario):
We analyze analytically and numerically the stress distribution along the plug-rock interface and within an axially loaded plug emplaced in a borehole in rock. Experiments show that the interface strength increases with decreasing plug radius and with increasing plug length. Axial strength decreases as a power law of plug radius. An increase in the modulus ratio (ratio of plug modulus to rock modulus) increases the interface strength, until it levels off at a ratio of about 5.0. For short plugs, the tensile stresses may reach a magnitude significant to be of concern for long-term stability of the plug and of the host rock. Out studies suggest designing friction plugs with a length to radius ratio of at least 8.0. In practice, especially for short-term performance, e.g., emergency flood control or temporary diversions, a ratio of 8.0 may not be necessary or justified. For permanent abandonment plugs, it is essential to reduce the tensile stresses in the plug and in the host rock to a level that will minimize the risk of long-term deterioration. We recommend in situ experiments on larger diameter plugs to assess the validity of the proposed size effect extrapolation obtained in this study. Key words: borehole plugging (sealing), shaft seal design, plug-rock interface strength, axial strength, bond strength, cement grout.
9
Akgün, Haluk, e Jaak JK Daemen. "Design implications of analytical and laboratory studies of permanent abandonment plugs". Canadian Geotechnical Journal 36, n. 1 (8 agosto 1999): 21–38. http://dx.doi.org/10.1139/t98-089.
Abstract (sommario):
We analyze analytically and numerically the stress distribution along the plug-rock interface and within an axially loaded plug emplaced in a borehole in rock. Experiments show that the interface strength increases with decreasing plug radius and with increasing plug length. Axial strength decreases as a power law of plug radius. An increase in the modulus ratio (ratio of plug modulus to rock modulus) increases the interface strength, until it levels off at a ratio of about 5.0. For short plugs, the tensile stresses may reach a magnitude significant to be of concern for long-term stability of the plug and of the host rock. Our studies suggest designing friction plugs with a length to radius ratio of at least 8.0. In practice, especially for short-term performance, e.g., emergency flood control or temporary diversions, a ratio of 8.0 may not be necessary or justified. For permanent abandonment plugs, it is essential to reduce the tensile stresses in the plug and in the host rock to a level that will minimize the risk of long-term deterioration. We recommend in situ experiments on larger diameter plugs to assess the validity of the proposed size effect extrapolation obtained in this study.Key words: borehole plugging (sealing), shaft seal design, plug-rock interface strength, axial strength, bond strength, cement grout.
10
Jiang, Ji Wei, Jun Li, Gong Hui Liu, Yan Xi e Wai Li. "Influence of Casing Pressure Test on Seal Integrity of Cementing First Interface". Materials Science Forum 944 (gennaio 2019): 1020–27. http://dx.doi.org/10.4028/www.scientific.net/msf.944.1020.
Abstract (sommario):
Casing pressure test is an important link of the oil and gas well cementing, but excessive casing pressure test may cause stress failure or plastically deformation of the cement sheath, and generate micro-annulus on the casing-cement sheath cemented surface, then lose seal integrity of the cement sheath. According to the basic theory of elastoplastic mechanics and considering the volume invariance of plastic strain and the influence of elastic strain on volume change, the Mohr-Coulomb criterion is used to establish the casing-cement sheath-surrounding rock combination model. The paper also derived the formula for calculating the micro-annulus of the casing pressure test, and analyzed the influence of the internal pressure of the casing during the pressure test and the elastic modulus of the cement sheath on the radial contact stress of the cement sheath cementation interface after the cementing operation is completed. Results show that: (1) The generation of micro-annulus of casing pressure test is determined by the pressure increase process and the pressure relief process. The pressure increase process may lead the cement sheath into plasticity, and the radial stress at the interface turns into tensile stress and the micro-annulus could appear at the first interface by the decrease of internal pressure during pressure relief process. (2) The varying internal pressure has a great influence on the fatigue failure of the cement sheath, so the continuous multiple casing pressure test should be avoided after the cementing is completed. (3) Under the condition of maintaining the integrity of the cement sheath, increasing the tensile strength of the cement stone and reducing the elastic modulus of the cement stone can improve the pressure bearing capacity of the first interface during the casing pressure test. The model can provide a theoretical basis for the mechanical parameter design of the cement sheath, and provide guidance for on-site construction to reduce or avoid the risk of failure of the first interface seal integrity for the casing pressure test.
11
Li, Daihong, Xiaoyu Zhang e Zhixiang Chen. "Study on the Hydraulic Fracturing of the Inter-Salt Shale Oil Reservoir with Multi-Interfaces". Processes 11, n. 1 (15 gennaio 2023): 280. http://dx.doi.org/10.3390/pr11010280.
Abstract (sommario):
Hydraulic fracture morphology and propagation mode are difficult to predict in layers of the various lithological strata, which seriously affects exploitation efficiency. This paper studies the fundamental mechanical and microscopic properties of the two main interfaces in inter-salt shale reservoirs. On this basis, cement-salt combination samples with composite interfaces are prepared, and hydraulic fracturing tests are carried out under different fluid velocities, viscosity, and stress conditions. The result shows that the shale bedding and salt-shale interface are the main geological interfaces of the inter-salt shale reservoir. The former is filled with salt, and the average tensile strength is 0.42 MPa, c = 1.473 MPa, and φ = 19.00°. The latter is well cemented, and the interface strength is greater than that of shale bedding, with c = 2.373MPa and φ = 26.15°. There are three basic fracture modes for the samples with compound interfaces. Low-viscosity fracturing fluid and high-viscosity fracturing fluid tend to open the internal bedding interface and produce a single longitudinal crack, respectively, so properly selecting the viscosity and displacement is necessary. Excessive geostress differences will aggravate the strain incompatibility of the interface between different rock properties, which makes the interfaces open easily. The pump pressure curves' morphological characters are different with different failure modes.
12
Jahanbakhsh, Amir, Qi Liu, Mojgan Hadi Mosleh, Harshit Agrawal, Nazia Mubeen Farooqui, Jim Buckman, Montserrat Recasens, Mercedes Maroto-Valer, Anna Korre e Sevket Durucan. "An Investigation into CO2–Brine–Cement–Reservoir Rock Interactions for Wellbore Integrity in CO2 Geological Storage". Energies 14, n. 16 (16 agosto 2021): 5033. http://dx.doi.org/10.3390/en14165033.
Abstract (sommario):
Geological storage of CO2 in saline aquifers and depleted oil and gas reservoirs can help mitigate CO2 emissions. However, CO2 leakage over a long storage period represents a potential concern. Therefore, it is critical to establish a good understanding of the interactions between CO2–brine and cement–caprock/reservoir rock to ascertain the potential for CO2 leakage. Accordingly, in this work, we prepared a unique set of composite samples to resemble the cement–reservoir rock interface. A series of experiments simulating deep wellbore environments were performed to investigate changes in chemical, physical, mechanical, and petrophysical properties of the composite samples. Here, we present the characterisation of composite core samples, including porosity, permeability, and mechanical properties, determined before and after long-term exposure to CO2-rich brine. Some of the composite samples were further analysed by X-ray microcomputed tomography (X-ray µ-CT), X-ray diffraction (XRD), and scanning electron microscopy–energy-dispersive X-ray (SEM–EDX). Moreover, the variation of ions concentration in brine at different timescales was studied by performing inductively coupled plasma (ICP) analysis. Although no significant changes were observed in the porosity, permeability of the treated composite samples increased by an order of magnitude, due mainly to an increase in the permeability of the sandstone component of the composite samples, rather than the cement or the cement/sandstone interface. Mechanical properties, including Young’s modulus and Poisson’s ratio, were also reduced.
13
Yokoyama, Shingo, Misato Shimbashi, Daisuke Minato, Yasutaka Watanabe, Andreas Jenni e Urs Mäder. "Alteration of Bentonite Reacted with Cementitious Materials for 5 and 10 years in the Mont Terri Rock Laboratory (CI Experiment)". Minerals 11, n. 3 (28 febbraio 2021): 251. http://dx.doi.org/10.3390/min11030251.
Abstract (sommario):
The cement–clay interaction (CI) experiment was carried out at the Mont Terri rock laboratory to complement the current knowledge on the influence that cementitious materials have on Opalinus Clay (OPA) and bentonite (MX). Drill cores including the interface of OPA, concrete (LAC = low-alkali binder, and OPC = ordinary Portland cement), and MX, which interacted for 4.9 and 10 years, were successfully retrieved after drilling, and detailed analyses were performed to evaluate potential mineralogical changes. The saturated compacted bentonites in core samples were divided into ten slices, profiling bentonite in the direction towards the interface, to evaluate the extent and spatial variation of the mineralogical alteration of bentonite. Regarding the mineral compositions of bentonite, cristobalite was dissolved within a range of 10 mm from the interface in both LAC-MX and OPC-MX, while calcite precipitated near the interface for OPC-MX. In LAC-MX and OPC-MX, secondary products containing Mg (e.g., M-S-H) also precipitated within 20 mm of the interface. These alterations of bentonite developed during the first 4.9 years, with very limited progress observed for the subsequent 5 years. Detectable changes in the mineralogical nature of montmorillonite (i.e., the formation of illite or beidellite, increase in layer charge) did not occur during the 10 years of interaction.
14
Zhan, Yubao, Nan Li, Hui Wang, Pengqiang Zheng, Jun Zhang e Qihua Liu. "The Mechanism of Interface Dilatancy of Cement Mortar Rockbolts". Advances in Civil Engineering 2020 (8 settembre 2020): 1–14. http://dx.doi.org/10.1155/2020/8838488.
Abstract (sommario):
In this paper, the mechanism of the interface dilatancy of cement mortar rockbolts is studied based on the phenomenon of splitting failure of samples with a high sand content in the grouting material in laboratory tests. A conceptual model of the interface layer is used to explain the dilatancy mechanism of the interface. Based on the thick-walled cylinder theory, the causes of splitting failure of the samples are analyzed. By using the numerical simulation method, the influences of different dilatancy angles of the interface layer on the interface shear stress and the radial stress are analyzed. The results show that the sand content of the grouting material has a substantial effect on the bearing capacity of the rockbolt. The higher the sand content in the grouting material is, the more obvious the interface dilatancy will be, and the greater the radial stress generated by dilatancy will be, which will produce a higher bearing capacity of the anchorage system. Under the same load, the maximum shear stress of the interface layer increases with increasing dilatancy angle. Similarly, the larger the dilatancy angle of the interface layer is, the greater the radial stress caused by dilatancy will be. Away from the interface layer, the radial stress decays rapidly. The influence range of the radial stress caused by dilatancy is mainly in the interface layer and the rock nearby.
15
Wasch, Laura, e Mariëlle Koenen. "Injection of a CO2-Reactive Solution for Wellbore Annulus Leakage Remediation". Minerals 9, n. 10 (22 ottobre 2019): 645. http://dx.doi.org/10.3390/min9100645.
Abstract (sommario):
Driven by concerns for safe storage of CO2, substantial effort has been directed on wellbore integrity simulations over the last decade. Since large scale demonstrations of CO2 storage are planned for the near-future, numerical tools predicting wellbore integrity at field scale are essential to capture the processes of potential leakage and assist in designing leakage mitigation measures. Following this need, we developed a field-scale wellbore model incorporating (1) a de-bonded interface between cement and rock, (2) buoyancy/pressure driven (microannulus) flow of brine and CO2, (3) CO2 diffusion and reactivity with cement and (4) chemical cement-rock interaction. The model is aimed at predicting leakage through the microannulus and specifically at assessing methods for CO2 leakage remediation. The simulations show that for a low enough initial leakage rate, CO2 leakage is self-limiting due to natural sealing of the microannulus by mineral precipitation. With a high leakage rate, CO2 leakage results in progressive cement leaching. In case of sustained leakage, a CO2 reactive solution can be injected in the microannulus to induce calcite precipitation and block the leak path. The simulations showed full clogging of the leak path and increased sealing with time after remediation, indicating the robustness of the leakage remediation by mineral precipitation.
16
Yang, Xinxiang, Siqi Guo e Ergun Kuru. "A Numerical Simulation Study of the Impact of Microchannels on Fluid Flow through the Cement–Rock Interface". Applied Sciences 12, n. 9 (9 maggio 2022): 4766. http://dx.doi.org/10.3390/app12094766.
Abstract (sommario):
Microchannels located at the cement–rock interface can form potential pathways for formation fluid leakage in oil and gas wells. The effects of geometric shape, quantity, and the inclination angle of microchannels on the flow through cemented rock samples were explored. Finite element 3D models were established based on modified micro-CT images obtained from physical samples. The volume flow rate through different sections of cemented rock samples was extracted after the fluid flow simulations. The numerical results showed that with the presence of a single microchannel, the total volume flow rate could be higher than that of the base case by as much as 9%. Microchannel contact and cross-sectional areas were found to be the two most important factors affecting the total volume flow rate. The overall volume flow rate increased with the increasing cross-sectional area, contact area, and inclination angle of the microchannel. The total volume flow rate for the cases with microchannels having the same cross-sectional area but different shapes increased with the decreasing number of sides of the shape (from circular to triangular) due to the increased contact area. The simulation results also revealed that the relative magnitude of the rock permeability may influence the volume flow rate through each section.
17
Mei, Can, Qing Fang, Haowei Luo, Jiangang Yin e Xudong Fu. "A Synthetic Material to Simulate Soft Rocks and Its Applications for Model Studies of Socketed Piles". Advances in Materials Science and Engineering 2017 (2017): 1–8. http://dx.doi.org/10.1155/2017/1565438.
Abstract (sommario):
A detailed manufacturing procedure of a synthetic soft rock is presented, as well as its applications on the laboratory experiments of socketed piles. With the homogeneity and isotropy of the simulated soft rock, the influence of different variables on the bearing performance could be investigated independently. The constituents, cement, gypsum powder, river sand, concrete-hardening accelerator, and water, were mixed to form the specimens. Both uniaxial and triaxial compressive tests were conducted to investigate the stress-strain behavior of the simulated soft rock. Additionally, the simulated soft rock specimens were used in model pile tests and simple shear tests of the pile-rock interface. Results of the simulated soft rock in both the uniaxial and triaxial compressive tests are consistent with those of natural soft rocks. The concrete-hardening accelerator added to the mixtures improves the efficiency in laboratory investigations of soft rock specimens with a curing time of 7 days. The similarities between the laboratory tests and the field observations provide convincing evidence to support its suitability in modeling the behavior of soft rocks.
18
Xu, Xiangqian, Weilv Wu e Wenbin Xu. "Sulfate-Dependent Shear Behavior of Cementing Fiber-Reinforced Tailings and Rock". Minerals 10, n. 11 (19 novembre 2020): 1032. http://dx.doi.org/10.3390/min10111032.
Abstract (sommario):
A better understanding of the shear behavior of the interface between cemented paste backfill (CPB) and the surrounding rock is critical for constructing cost-effective, durable, and reliable CPB structures. In practice, CPBs suffer sulfate attack during their service life, and as a typical cementitious material, the CPB itself has disadvantages, such as high brittleness, easy cracking, and insufficient durability, which restrict the further popularization and application of CPB technology. Thus, in this study, direct shear tests, electrical conductivity (EC) and thermal gravity/differential thermal gravimetric (TG/DTG) analyses were conducted to research the effects of different amounts of monofilament polypropylene fibers (0%, 0.1%, 0.3%, and 0.5%; by mass of the sum of the dry tailings and cement) and initial sulfate concentrations (0 mg/L, 5000 mg/L and 25,000 mg/L) on the shear behavior of the fiber-reinforced CPBs and rock (FR-CPB/rock) interface, and the Mohr–Coulomb shear envelop was used to fit the shear strength of specimens with various periods (1 day, 3 days, 7 days, and 28 days) under various stresses (50 kPa, 100 kPa, 150 kPa). The experimental testing results indicated that the fibers generally enhance the performance of the shear behavior of the FR-CPB/rock interface and the optimal fiber content correlates to the initial sulfate concentration. For the same treatment time (7 days), a fiber content of 0.1% contributes to the best shear performance for the FR-CPB/rock interface with a sulfate concentration of 5000 mg/L. For the sulfate-free and 25,000 mg/L concentration specimens, 0.3% is the optimal fiber content. Furthermore, for the studied interface specimens, sulfate content can play a positive (the refinement of the pore structure) or negative (the sulfate retardation effect) role in the interface shear behavior between the FR-CPB and rock, depending on the treatment time, the initial sulfate concentration, and the fiber content. For the specimens treated for 7 days and 28 days, the specimens with initial sulfate concentrations of 5000 mg/L and 25,000 mg/L achieved the highest peak shear strengths, respectively. The outcomes of this paper present a substantial reference for the design and optimization of underground FR-CPB structures under sulfate attack.
19
Holý, Ondřej. "Results and Use of Non-Linear Behavior Between Length and Bond Friction of Fully Grouted Rock Bolts in Selected Jointed Rock Masses". GeoScience Engineering 64, n. 2 (1 giugno 2018): 26–39. http://dx.doi.org/10.2478/gse-2018-0010.
Abstract (sommario):
Abstract The anchor length db of rock bolts is often determined empirically by the insertion of the bond friction constant τb at the grout-rock interface. The relationship between force Fb by limit bond stress and bond length (or bond area) is their ratio. Within the same location, the anchor length can be overestimated or underestimated by usage τb = constant. In this paper, the results of load tests of passive rock bolts were analyzed across the many rocks of the Bohemian Massif using selected parameters (RQD index, GSI values, bulk density ρv, uniaxial compressive strength UCS) and their correlation. It was found that the relationship between the anchor length and the limit bound friction is non-linear and is influenced by selected parameters and the type of anchor grouting material (cement and resin). It was considered a state where τb = f (db, Fb, ρv, UCS, RQD, GSI) for 3 types of bonding (1-cement sealing, 2-cement grouting, 3-mixing of resin cartridge). The achieved and measured bond friction was verified by solving the polynomial roots using the CG (conjugate gradient) method. The accuracy of the results reached the maximum mean difference value absΔτb = 0.02 MPa and the standard deviation SD = 0.058. With this verified model, a simulation of random variables was performed by the Monte Carlo method for Fb = const. with the uniform and normal distribution with n = 1500 samples. The results were converted to diagrams represented by the mean value of the uniform distribution (best fit curves) and the normal distribution envelope curves (for 3σ).
20
Alves, C., C. Figueiredo, A. Maurício e L. Aires-Barros. "Salt weathering of limestones: susceptibility of petrographical features (SEM study)". Microscopy and Microanalysis 19, S4 (agosto 2013): 113–14. http://dx.doi.org/10.1017/s1431927613001189.
Abstract (sommario):
Salt weathering is one of the main processes affecting rock materials applied in the built environment. Scanning electron microscopy (SEM) studies can contribute to the understanding of the susceptibility of petrographic features of rocks to salt weathering.SEM studies were performed in limestones (grainstones with the commercial designations of Semi-rijo and Moca Creme and a travertine) submitted to salt weathering tests (EN 12370 using sodium sulphate solutions and cubic specimens) consisting of 15 cycles of immersion/drying followed by water washing after the 15th cycle. Fragments from small cubes of the grainstones subjected to salt weathering cycles without the final water cleaning were also studied. SEM observation before and after the tests allows the discussion of the petrographical characteristics of these rocks that contribute to erosive decay under salt weathering.In the case of the grainstones specimens the texture can be described in general as allochemical particles cemented by sparry calcite (Figure 1 a) and it is visible from the preparation of the polished surfaces the interface between the sparry cement and the allochemical components. After the salt weathering tests, SEM studies show (Figure 1 b) extensive fissuring in the sparry cement and separation between grains and sparry cement. Observations of disaggregation products showed an important amount of apparently intact grains. These results are similar to those observed by with the sparry cement being affect by salt crystallisation and lesser impact on the grains. Studies in the unwashed specimens showed the presence of sodium sulphate in the interface between allochemical grains and the sparry cement (Figure 1 c,d). Travertine specimens show heterogeneous patterns of erosion attributed to the heterogeneous texture of this rock, with more terrigenous (especially clay-rich) portions that favour a higher erosive susceptibility and the presence of clays has been frequently connected with salt weathering susceptibility in limestones. In Figure 1e can be observed the heterogeneity of a polished surface, with the more irregular portions showing a chemical spectra (Figure 1 f) indicative of the terrigenous component and the presence of sodium and sulphate (resulting from the solutions used in these weathering tests).The authors acknowledge the support of the Fundação para a Ciência e Tecnologia (POCTI/CTA/44940/2002; PEst-OE/CTE/UI0697/2011 and Pest-OE/CTE/UI0098/2011, funding by the European Union and national budget of the Portuguese Republic). Acknowledgments to Eng. Teresa Luís, Eng. Sónia Pereira and Enterprise Mármores Galrão for the rock blocks.
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Watson, C., D. Savage, J. Wilson, S. Benbow, C. Walker e S. Norris. "The Tournemire industrial analogue: reactive-transport modelling of a cement–clay interface". Clay Minerals 48, n. 2 (maggio 2013): 167–84. http://dx.doi.org/10.1180/claymin.2013.048.2.02.
Abstract (sommario):
AbstractIn the post-closure period of a geological disposal facility for radioactive waste, leaching of cement components is likely to give rise to an alkaline plume which will be in chemical disequilibrium with the host rock (which is clay in some concepts) and other engineered barrier system materials used in the facility, such as bentonite. An industrial analogue for cement-clay interaction can be found at Tournemire, southern France, where boreholes filled with concrete and cement remained in contact with the natural mudstone for 15–20 years. The boreholes have been overcored, extracted and mineralogical characterization has been performed. In this study, a reactive-transport model of the Tournemire system has been set up using the general-purpose modelling tool QPAC. Previous modelling work has been built upon by using the most up-to-date data and modelling techniques, and by adding both ion exchange and surface complexation processes in the mudstone. The main features observed at Tournemire were replicated by the model, including porosity variations and precipitation of carbonates, K-feldspar, ettringite and calcite. It was found that ion exchange needed to be included in order for C-S-H minerals to precipitate in the mudstone, providing a better match with the mineralogical characterization. The additional inclusion of surface complexation, however, led to limited calcite growth at the concrete-mudstone interface unlike samples taken from the Tournemire site that have a visible line of crusty carbonates along the interface.
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Xu, Honglin, Nian Peng, Tianshou Ma e Bin Yang. "Investigation of Thermal Stress of Cement Sheath for Geothermal Wells during Fracturing". Energies 11, n. 10 (27 settembre 2018): 2581. http://dx.doi.org/10.3390/en11102581.
Abstract (sommario):
Geothermal energy development has increasingly been studied in recently decades because of its renewable and sustainable features. It can be divided into two categories: traditional geothermal (hydrothermal) systems and enhanced geothermal systems (EGS) based on the type of exploitation. The hot dry rock (HDR) in the EGS incorporates about 80% of all thermal energy, and its value is about 100–1000 times that of fossil energy. It is pivotal for geothermal wells to improve the flow conductivity of the HDR mass, enhance the communication area of natural fractures, and constitute the fracture network between injection and production wells by hydraulic treatments. While the wellbore temperature significantly decreases because of fracturing, fluid injection will induce additional thermal stresses in the cement sheath, which will aggravate its failure. Considering the radial nonuniform temperature change, this paper proposes a new thermal stress model for a casing-cement sheath-formation combined system for geothermal wells during fracturing based on elastic mechanics and thermodynamics theory. This model is solved by the Gaussian main elimination method. Based on the analytical model, the thermal stresses of cement sheath have been analyzed. The effects of the main influencing parameters on thermal stresses have also been investigated. Results show that the radial and axial tensile thermal stresses are both obviously larger than tangential tensile thermal stress. The maximum radial and axial thermal stresses always occur at the casing interface while the location of the maximum tangential thermal stress varies. Generally, thermal stresses are more likely to induce radial and axial micro cracks in the cement sheath, and the cement sheath will fail more easily at the casing interface in fracturing geothermal wells. For integrity protection of the cement sheath, a proper decrease of casing wall thickness, casing linear thermal expansion coefficient, cement sheath elasticity modulus, and an increase of the fracturing fluid temperature has been suggested.
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Yang, Yang, Niannian Zhang e Jianguo Wang. "Fracture Morphology Analysis of Frozen Red Sandstone under Impact". Shock and Vibration 2021 (23 dicembre 2021): 1–12. http://dx.doi.org/10.1155/2021/4388132.
Abstract (sommario):
The deformation and failure characteristics of red sandstone under subzero temperature were studied by the split Hopkinson pressure bar (SHPB) dynamic impact test. The effects of different subzero temperatures on rock strength properties, fractal dimension, and dissipated energy were analyzed combined with microfracture morphology. The reasons for rock dynamic mechanical property deterioration under lower subzero temperatures were revealed. The research shows that low subzero temperature will cause “frostbite” of red sandstone. Under high strain rate loading, the rock will quickly lose its bearing capacity, and its dynamic mechanical strength will drop sharply. The dissipated energy W L of the frozen rock specimen is positively correlated with the fractal dimension D and closely related to the macroscopic failure characteristics. It could be concluded that greater dissipation energy leads to more serious damage of rock and accordingly results in a larger fractal dimension. Fracture morphology analysis shows that the lower subzero temperature generated remarkable cracks in the material interface of the red sandstone. The damage of the red sandstone could be explained by the fact that the crack tip had low plastic deformation ability under high strain rate loading and the composition of cement was vulnerable to the subzero temperature effect.
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Zhang, Chunmei, Jingxuan Cai, Xiaowei Cheng, Xingguo Zhang, Xiaoyang Guo e Yuntao Li. "Interface and crack propagation of cement-based composites with sulfonated asphalt and plasma-treated rock asphalt". Construction and Building Materials 242 (maggio 2020): 118161. http://dx.doi.org/10.1016/j.conbuildmat.2020.118161.
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Yin, Yu-shi, e Ying-fang Fan. "Experimental research on the wet bonding properties between RFRP and concrete". Advances in Structural Engineering 23, n. 5 (10 novembre 2019): 857–68. http://dx.doi.org/10.1177/1369433219882774.
Abstract (sommario):
In this work, an improved wet bonding method was developed for strengthening of fiber-reinforced polymer. A self-made roughened carbon fiber–reinforced polymer sheet (hereinafter referred to as RFRP sheet) was externally attached to the surface layer of a nano-kaolin-modified concrete test piece to form an RFRP–concrete wet-bonded test piece. Then, the pull-off bond test and the single shear test were performed on 32 and 30 test pieces, respectively. The performance of the wet bonding interface of RFRP–concrete in the normal and tangential directions was investigated by changing the length of glass fiber cellosilk in RFRP bonding resin, the diameter of RFRP porous pelelith rock, and the ratio of nano-kaolin. In addition, by comparing the scanning electron microscopy images of untreated fiber-reinforced polymer sheet and the concrete block without nano-kaolin, the mechanism of the adhesion enhancement of the RFRP–concrete interface was explained. The results show that the differentiation between fiber-reinforced polymer–concrete wet bonding failure and RFRP–concrete wet bonding failure was mainly based on the large-scale concrete with peeled off concrete surface. RFRP effectively enhanced the wet adhesion performance of the interface with concrete in both normal and tangential directions. The interface bonding ability increased by 900% and 42%, respectively, compared with the control test pieces. The diameter of pelelith rock was found to be the most important factor affecting the shear wet bonding performance of the RFRP–concrete interface. The second important factor was the ratio of nano-kaolin. The optimum conditions for the best tangential anti-peeling ability of the RFRP–concrete structure were found to be the addition of 5-mm-diameter pelelith stone, 3% nano-kaolin, and glass cellosilk of 89 mm length. When the RFRP and the concrete were wet-bonded, the uncured cement mortar effectively filled the holes of the original pelelith rock and acted as a mechanical lock, thereby increasing the bonding stress.
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Xiao, Ting, Brian McPherson, Amanda Bordelon, Hari Viswanathan, Zhenxue Dai, Hailong Tian, Rich Esser, Wei Jia e William Carey. "Quantification of CO2-cement-rock interactions at the well-caprock-reservoir interface and implications for geological CO2 storage". International Journal of Greenhouse Gas Control 63 (agosto 2017): 126–40. http://dx.doi.org/10.1016/j.ijggc.2017.05.009.
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Liu, Weitao, Yueyun Qin, Xiangxi Meng, Lifu Pang, Mengke Han e Zengmou Song. "Basic Experimental Study of Plasticity Material for Coal Rock Fracture Grouting Based on RSM-PCA Technology". Energies 14, n. 15 (26 luglio 2021): 4516. http://dx.doi.org/10.3390/en14154516.
Abstract (sommario):
The internal fractures in coal and rock mass are important factors affecting the safety of underground engineering such as coalbed methane exploitation, so the comprehensive properties of materials used to seal the fractures are particularly critical. In this paper, firstly, the indexes of the main factors affecting the plugging material (viscosity, bleeding rate, setting time, and strength) were analyzed. Then, the sensitivity of the materials used to seal the fractures was studied and discussed using a principal component analysis and response surface analysis (RSM-PCA). The primary conclusions are as follows: (1) Bleed rate and setting time were the first principal components affecting the comprehensive properties of the plugging materials, and compressive strength was the second principal component. (2) The regression equation was established to characterize the comprehensive properties of the integrated plugging materials, and the optimal mix ratio was 34% of cement content, 11% of sand content, and 0.53 of the W/C. (3) The microscopic results showed that the silicate minerals in the consolidated body grow in a bridging manner and formed a mixed gel with cement hydration product to fill the pores and microcracks and improved the interface transition zone.
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Castelletto, N., M. Ferronato, G. Gambolati, C. Janna e P. Teatini. "Numerical Modeling of Rock/Casing Interaction in Radioactive-Marker Boreholes of the Northern Adriatic Basin, Italy". SPE Reservoir Evaluation & Engineering 13, n. 06 (23 agosto 2010): 906–13. http://dx.doi.org/10.2118/135736-pa.
Abstract (sommario):
Summary The possible influence of the well casing in reservoir-deformation measurements by the radioactive-marker technique (RMT) is investigated. The issue is quite important because RMT data may be used for a most-representative estimate of the in-situ vertical rock compressibility cM (i.e., a basic parameter to predict the land settlement caused by gas-/oilfield development or the land uplift caused by underground fluid injection). A geomechanical finite-element (FE) model is implemented to evaluate the disturbance caused by the stiffness of the steel casing and the surrounding cement on the amount of deformation around the borehole as detected by RMT. The FE model is integrated by a class of elastoplastic interface FEs (IFEs) specifically designed to account for the potential sliding of the different materials (i.e., along the contact surfaces between the steel casing and the cement, and the cement and the exploited formation). The numerical simulations make use of real casing data and geomechanical information from the Northern Adriatic basin, Italy. The results show that sliding is not likely to occur along the contact surfaces and that RMT appears to be a reliable tool for assessing the actual geomechanical properties of the depleted formation at a depth larger than 1000 m, where the in-situ deformation is negligibly affected by the casing stiffness. In shallow softer units, the compaction as measured by RMT is influenced progressively by casing, with a corresponding likely underestimate of cM.
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Liu, Jie, Hongya Li, Yunzhou Li, Yunan Yang, Tao Sun, Rui Song e Rongqi Sun. "Study on the Effect of Isotropic Initial Stress on the Anchoring Performance of Self-Expanding Bolts". Advances in Civil Engineering 2021 (11 marzo 2021): 1–19. http://dx.doi.org/10.1155/2021/6678947.
Abstract (sommario):
In order to study the anchoring performance of a new type of self-expanding, high-strength, precompression anchoring technology with a large amount of expansion agent (ω ≥ 5) cement slurry as anchoring solids under confined surrounding rock conditions, a rock mass anchoring device and methods that simulate in situ stress are developed, and real-time monitoring of expansion stress and anchor pull-out tests are carried out. The results show that the internal interface stress has a loss effect over time, and the stress loss value shows a linear increase trend with the dosage, but the loss rate shows a linear decreasing relationship with the dosage. This paper defines the coordinated additional stress and obtains its temporal and spatial evolution law in the rock mass. It is pointed out that there is a lag time difference between the peak of internal interface stress and the peak of coordinated additional stress, explaining its mechanical mechanism from the perspective of stress transfer. The strong restraint of the sealing section of the anchor hole causes the anchor solid to form a “shuttle-shaped” microexpanded head with thin ends and a middle drum under the expansion stress. During the drawing process, the microexpanded head is “stuck” in the anchor hole and moves upward to form the unique “load platform effect” of the anchoring system. And the mechanical mechanism diagram of this effect is obtained. It is pointed out that this effect can greatly improve the ductility of the anchoring system and the ultimate energy consumption value of damage. A prediction model for the ultimate pull-out force of self-expanding bolts is established. It is pointed out that the initial confining stress value has an exponential effect on the ultimate pull-out force. It shows that the surrounding rock with strong confinement constraints can greatly increase the ultimate pull-out resistance of the bolt. The self-expanding strengthening coefficient λ and the surrounding rock stress influence coefficient k are introduced, the bolt interface mechanics formula and energy equation of the self-expanding anchor system are established, and the feasibility of the formula is verified by the calculation example. It is concluded that the ultimate pull-out resistance of the anchorage with ω = 30 is increased by 3.38 times compared with the ordinary anchorage under the initial confining stress condition of 0.7 MPa, the prepeak displacement of the bolt is increased by 2.08 times, and the prepeak energy consumption of the anchoring system is increased by 7.34 times. The cost only increased by 0.023% based on the literature example.
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Kremieniewski, Marcin, Rafał Wiśniowski, Stanisław Stryczek e Paweł Łopata. "Comparison of Efficient Ways of Mud Cake Removal from Casing Surface with Traditional and New Agents". Energies 14, n. 12 (19 giugno 2021): 3653. http://dx.doi.org/10.3390/en14123653.
Abstract (sommario):
The tightness of the casing-rock formation interface is one of the most important elements of drilling and cementing jobs. In the absence of the required tightness, there is a risk of gas migration directly to the ground, groundwater or atmosphere. In order to eliminate this type of uncontrollable and unfavorable gas flows, the casing column is sealed with cement slurry in the annular space or beyond casing. Cement slurry displaces mud present in the annular space, although the mud cake cannot be completely removed, which is required for obtaining proper binding of cement slurry with the casing surface and the surface of the drilled formation. Therefore, it is important to prepare the well and remove the mud cake from the annular space with spacer fluid. An occasional lack of wellbore tightness requires continuous improvement of the cementing technology. Accordingly, analyses are conducted on mud cake removal with modified or new spacer fluids. Properly designed fluid should efficiently clean the surface of the casing and of the rock mass. One of the basic measurements is the analysis of the efficiency of mud cake removal from the surface of a rotational viscometer. The efficiency of traditional and newly designed fluids for mud cake removal from the casing surface with new and traditional agents has been compared further in this paper. The methodology of mud cake removal with the use of a rotational viscometer was also presented. Tests were performed for various concentrations of agents already used for spacer fluids and for a group of new agents. The efficiency of annular space cleaning was determined on the basis of a comparison with the results obtained for the reference sample, i.e., water which was used for mud cake removal from the rotor surface. The analysis of the results of experiments created bases for the comparison of the efficiency of the analyzed spacer fluids and finding the most suitable ones for mud cake removal from casing columns.
31
Gaona, Xavier, Marcus Altmaier, Iuliia Androniuk, Nese Çevirim-Papaioannou, Michel Herm, Luis Iglesias-Perez, Yongheum Jo et al. "Cement as a component of the multi-barrier system: radionuclide retention in cementitious environments". Safety of Nuclear Waste Disposal 1 (10 novembre 2021): 151–52. http://dx.doi.org/10.5194/sand-1-151-2021.
Abstract (sommario):
Abstract. Safety concepts regarding nuclear waste disposal in underground repositories generally rely on a combination of engineered and geological barriers, which minimize the potential release of radionuclides from the containment-providing rock zone or even their transport into the biosphere. Cementitious materials are used for conditioning of certain nuclear waste types, as components of waste containers and overpacks, as well as being constituents of structural materials at the interface between backfilling and host rock in some repository concepts. For instance, the preferred option for the disposal of high-level waste (HLW) in Belgium is based on the supercontainer design, which consists of a carbon steel overpack surrounded by a thick concrete buffer (Bel et al., 2006). In the event of formation water interacting with cementitious materials, pore water solutions characterized by (highly) alkaline pH conditions will form. These boundary conditions define the chemical response of the radionuclides, but also influence the behaviour of neighbouring components of the multi-barrier system, e.g. bentonitic or argillaceous backfilling and host rock. Hardened cement paste or Sorel cement are considered to be main sorbing materials present in the near field of repositories for low- and intermediate-level waste (L/ILW). Hence, interactions of radionuclides with cementitious materials represent a very important mechanism retarding their mobility and potential migration from the near field (Wieland, 2014; Ochs et al., 2016). While the quantitative description of the sorption processes (usually in terms of sorption coefficients, i.e. Kd values) is a key input in the safety analysis of nuclear waste repositories, detailed mechanistic analysis and understanding of sorption phenomena provide additional scientific arguments and important process understanding, and thus enhance both the quality of safety arguments and the overall confidence in the safety assessment process. Research at KIT-INE dedicated to the interaction of cementitious materials with radionuclides is conducted in the context of different repository concepts, including clay (low- and high-ionic strength conditions), crystalline rock or rock salt. Experimental and theoretical studies are performed within the framework of national (GRAZ, BMWi) and international (CEBAMA and EURAD-CORI, EU Horizon 2020 Programme) projects, extending to third-party projects with several waste management organizations in Europe, e.g. SKB (Sweden), ONDRAF-NIRAS (Belgium) or BGE (Germany). The combination of classical experimental (wet chemistry) methods, advanced spectroscopic techniques and theoretical calculations provides both an accurate quantitative evaluation and a fundamental understanding of the sorption processes. Examples of recent studies at KIT-INE on radionuclide behaviour in cementitious systems in the context of both L/ILW and HLW will be presented in this contribution to explain methodologies, scientific approaches and results. The present state of knowledge as well as main remaining uncertainties affecting the retention processes of radionuclides in cementitious environments under different conditions will be critically discussed, also in view of current international research activities and repository projects.
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Carpenter, Chris. "Hydraulic Fracturing Fluid Interactions With Steel, Cement, and Shale Measured". Journal of Petroleum Technology 74, n. 09 (1 settembre 2022): 91–93. http://dx.doi.org/10.2118/0922-0091-jpt.
Abstract (sommario):
_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper URTeC 3722736, “The Impact of Hydraulic Fracturing Fluid on the Near-Wellbore Shale Region Involving Interactions With Steel, Cement, and Shale,” by Wei Xiong, Brandon McAdams, and Mengling Stuckman, National Energy Technology Laboratory, et al. The paper has not been peer reviewed. _ Numerous studies have been conducted on rock/fluid interactions of deep shale reservoirs exposed to hydraulic fracturing fluid (HFF). However, the effect of fluid/steel/cement components on the chemistry of the near-wellbore shale region has been overlooked. In the study described in the complete paper, steel, cement, and shale samples were exposed to HFF sequentially in the same batch for 3 days at 66°C. Unlike the reaction of fresh HFF to direct exposure to shale, the fluid chemistry and exposed surfaces of steel and cement were altered significantly after exposure. Methods Sequential Exposure Experiment. For the sequential exposure batch, three steel coupons were placed at the bottom of a borosilicate bottle with 300 mL of HFF. After 3 days of exposure, all three steel coupons were removed. 100 mL of the reacted fluid was collected and filtered for fluid-chemistry analysis. Then, two cement coupons were placed in the bottle to react with the remaining 200 mL of fluid at the same temperature. After 3 days of reaction, the two cement coupons were removed with 100 mL of fluid as a liquid sample. Finally, one shale sample was placed in the bottle, exposed to the remaining 100 mL of fluid for 3 days. A controlled group using individual coupons was the subject of experiments using the same setup. One steel, cement, or shale coupon was placed in each bottle with 100 mL of HFF individually. A blank group with 100 mL of HFF without any coupons also was set up at the same conditions. These control groups reacted for 3 days. Analytical Methods. A three-electrode voltametric system was composed of a mercury/gold (Hg/Au) amalgam 100-µm-disc working electrode (WE), a solid-state silver/silver-chloride (Ag/AgCl) reference electrode (RE), and a platinum wire counter, or auxiliary, electrode (CE). The species undergoes oxidation or reduction at the WE interface at a potential measured against the potential of the RE wherein any exchange of electrons at the WE interface is compensated by the CE to complete the circuit within the potentiostat. Peaks observed in complex solutions like those in this study can be compared with known responses in previous studies to arrive at a qualitative assessment of what is happening, and when, in these solutions with respect to redox chemistry. For the purposes of continuity, all potentials reported in the complete paper are in relation to the Ag/AgCl reference electrode and require a positive adjustment of approximately 0.21 V.
33
Wu, Bo, e Wei Huang. "Uniaxial Compression Mechanical Properties of Rock Samples in Soft and Hard Composite Strata". Advances in Materials Science and Engineering 2020 (23 giugno 2020): 1–9. http://dx.doi.org/10.1155/2020/5920348.
Abstract (sommario):
In the upper soft and lower hard composite strata, it is very difficult to sample the rock and test the mechanical properties of the samples. The study of the mechanical properties of similar material samples by artificial manufacture may enable an alternative method to solve this problem. Therefore, the feasibility of artificial sample preparation and the test of mechanical properties of rock samples in the composite strata become the key to solve the study of mechanical properties of the upper soft strata and the lower hard composite strata. For this purpose, the artificial composite samples composed of two kinds of materials with different strengths were prepared by using cement and kaolin as similar materials. Through the uniaxial compression test of artificial composite rock samples, the effects of the strength ratio of similar materials and the thickness ratio of higher strength materials on the mechanical properties of composite specimens were analyzed. The results of uniaxial compression test show that artificial similar materials could be used to simulate the composite rock samples which are difficult to sample. Without considering the structural interface effect, the greater the strength ratio of similar materials, the greater the impact on the overall strength of composite specimens. The change of volume proportion of high-strength materials has a significant impact on the overall strength of composite specimens. Moreover, the numerical simulation and the experimental stress-strain curves both show a similar trend, indicating that the deformation of the composite strata mainly occurs in the soft part. The research results can provide reference for the test and analysis of mechanical properties in similar complex strata with difficult sampling.
34
Cai, Zhixiang, Hui Zhang, Kerou Liu, Yufei Chen e Qing Yu. "Experimental Investigation and Mechanism Analysis on Rock Damage by High Voltage Spark Discharge in Water: Effect of Electrical Conductivity". Energies 13, n. 20 (18 ottobre 2020): 5432. http://dx.doi.org/10.3390/en13205432.
Abstract (sommario):
High voltage spark discharge (HVSD) could generate strong pressure waves that can be combined with a rotary drill bit to improve the penetration rate in unconventional oil and gas drilling. However, there has been little investigation of the effect of electrical conductivity on rock damage and the fragmentation mechanism caused by HVSD. Therefore, we conducted experiments to destroy cement mortar, a rock-like material, in water with five conductivity levels, from 0.5 mS/cm to 20 mS/cm. We measured the discharge parameters, such as breakdown voltage, breakdown delay time, and electrical energy loss, and investigated the damage mechanism from stress waves propagation using X-ray computed tomography. Our study then analyzed the influence of conductivity on the surface damage of the sample by the pore size distribution and the cumulative pore area, as well as studied the dependence of internal damage on conductivity by through-transmission ultrasonic inspection technique. The results indicated that the increase in electrical conductivity decreased the breakdown voltage and breakdown delay time and increased the energy loss, which led to a reduction in the magnitude of the pressure wave and, ultimately, reduced the sample damage. It is worth mentioning that the relationship between the sample damage and electrical conductivity is non-linear, showing a two-stage pattern. The findings suggest that stress waves induced by the pressure waves play a significant role in sample damage where pores and two types of tensile cracks are the main failure features. Compressive stresses close horizontal cracks inside the sample and propagate vertical cracks, forming the tensile cracks-I. Tensile stresses generated at the sample–water interface due to the reflection of stress waves produce the tensile cracks-II. Our study is the first to investigate the relationship between rock damage and electrical conductivity, providing insights to guide the design of drilling tools based on HVSD.
35
Yu, Xiaocong, Xueqi Cen, Changbin Kan, Yilin Hu, Yanxing Yang, Shilin Tao, Xinyuan Chen, Xiupeng Chen e Zhiqiang Hu. "Numerical Simulation Analysis of Wellbore Integrity and Casing Damage in High-Temperature Injection and Production of Shale Oil". Processes 11, n. 11 (24 ottobre 2023): 3053. http://dx.doi.org/10.3390/pr11113053.
Abstract (sommario):
Shale oil represents a relatively new form of unconventional oil and gas resource, and the extensive exploration and development of shale oil resources carry significant implications for China’s oil and gas supply and demand dynamics. At present, within the realm of low-maturity shale oil extraction technologies, the reservoir must be subjected to elevated temperatures ranging between 400 to 60 °C. Prolonged exposure of wellbores to such high temperatures can result in a substantial decrease in cement strength, the formation of microcracks due to cement cracking, and damage stemming from thermal stresses on the casing. Casing damage stands out as a prominent factor contributing to wellbore integrity failures and well shutdowns within the context of shale oil development. Given the limited natural energy reservoirs of shale oil formations, it becomes necessary to supplement the reservoir’s energy during the development process. Furthermore, shale oil exhibits high viscosity and poor flowability, and conventional water injection methods yield limited efficacy. This situation can induce significant shifts in the stress field and rock mechanical parameters, potentially activating specific formations and complicating the load dynamics on the casing. Consequently, the risk of failure increases. In light of these considerations, this study uses numerical simulations to study the integrity of high-temperature injection and production wellbores in shale oil and aims to encompass a comprehensive evaluation and analysis of the principal factors that influence casing damage, the fluctuations in thermal stress, and the yield strength of various steel grades of casings exposed to alternating stress conditions. Subsequently, this paper developed a model for simulating the temperature and pressure within shale oil and steam injection wellbores to support engineering design analysis. The research results indicate that the application of pre-stress results in a significant increase in stress at the casing pipe head while causing a noticeable decrease in stress within the pipe wall. When N80 casing is used, the entire casing experiences thermal stresses surpassing the casing’s yield limit. Stress concentration may arise at both ends of the external seal, potentially leading to casing contraction, shear failure, and, under non-uniform stress conditions, casing bending deformation. The temperature of steam injection significantly influences the temperature field of the casing wall, with stress values experiencing a marked reduction when the steam injection temperature decreases from 350 °C to 200 °C, underscoring the substantial impact of temperature on casing thermal stress. As the steam injection process advances along with injection-production cycles, shear stresses at the interface can exceed the bond strength, resulting in relative slippage between the cement and the casing. The bonding force between the wellbore and the cement primarily depends on the interface’s friction, particularly in the context of friction during wellhead lifting. This study endeavors to determine rational injection and production parameters under varying conditions, optimize completion methods, reduce casing damage, and extend the casing’s operational life; it aims to offer critical technical support for the safe and efficient development of shale oil resources.
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Anderson, Noah T., Clinton A. Cowan e Kristin D. Bergmann. "A case for the growth of ancient ooids within the sediment pile". Journal of Sedimentary Research 90, n. 8 (19 agosto 2020): 843–54. http://dx.doi.org/10.2110/jsr.2020.45.
Abstract (sommario):
ABSTRACT In modern ooid-forming environments in the Caribbean, aerobic respiration of organic matter below the sediment–water interface drives an increase in pCO2 and a corresponding decrease in carbonate saturation state (Ω) that creates shallow sediment porewater that is neutral or slightly caustic to carbonate. The locus of ooid growth, therefore, is presumed to be in the water column during suspension, where supersaturation with respect to calcium carbonate is the norm. In the past, however, during conditions of low aqueous O2, high Ω, or low organic-matter input, the shallow sub-sediment marine burial environment was conducive to carbonate precipitation. Here we present petrographic and electron probe microanalyzer (EPMA) data from exquisitely preserved oolites through time that suggests that some ancient ooids may have grown within the sediment pile. We propose that each increment of ooid cortical growth originated as incipient isopachous marine cement formed during shallow burial within migrating ooid dunes. After a period of burial (∼ weeks to months), ooids were remobilized and rounded during bedload transport. This “bedform model” for ooid growth explains: 1) why ancient ooids are not limited by the precipitation–abrasion balance that appears to prohibit modern tangential Caribbean ooids from achieving grain sizes larger than coarse sand, 2) the radial crystal fabric that defines the internal structure of many ancient ooids, and 3) the first-order correlation of the abundance of large and giant ooids in the rock record to periods with predicted high porewater Ω. This model implies that photosynthetic microbes were unimportant for growth of large and giant ooid but it remains agnostic to the effect of other microbes. The physical and chemical milieu of modern marine ooid-forming environments is perhaps not the best analogue for ancient ooid-forming environments; this should be considered when using ancient ooids to reconstruct secular trends in ocean chemistry.
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Al Balushi, Said A. K., e Joe H. S. Macquaker. "Sedimentological evidence for bottom-water oxygenation during deposition of the Natih-B Member intrashelf-basinal sediments: Upper Cretaceous carbonate source rock, Natih Formation, North Sultanate of Oman". GeoArabia 16, n. 2 (1 aprile 2011): 47–84. http://dx.doi.org/10.2113/geoarabia160247.
Abstract (sommario):
ABSTRACT Geologists have commonly argued that the deposition of the excellent carbonate source rock (up to 13.7% total organic carbon) in the Upper Cretaceous Natih-B Member intrashelf basin (water depth circa 50 m) was mainly controlled by the presence of bottom-water “anoxia” in the basin centre. Some authors have even linked the formation of the Natih-B organic-carbon-rich sediments to the global development of “oceanic anoxia” that occurred a number of times during the Late Cretaceous. Recent research, however, suggests that the mechanisms that underpin organic-carbon enrichment in intrashelf-basinal settings are complicated and, instead, controlled by the complex interplay of variations in primary production of organic carbon, clastic dilution, bottom-water anoxia, early diagenesis and optimising rates of sediment accumulation, and are not necessarily related to global-forcing mechanisms. In this study, the requirement for persistent bottom-water anoxic conditions for the preservation of organic matter in this setting is assessed, evidence for oxic/dysoxic bottom-water conditions during deposition of the Natih-B organic-carbon-rich sediments is presented, and alternative models to explain organic-matter enrichment are considered. Natih-B sediments (collected both spatially and temporally from both core and exposures in North Oman) have been investigated using a combination of optical and electron-optical (backscattered electron imagery) techniques, which provide additional data to those gathered by traditional field and geochemical methods. Natih-B lithofacies alternate between two main types: organic-carbon-rich carbonate mudstones and calcite-cement-rich wackestones. The organic-rich mudstones are typically fine grained, dark grey, exhibit remnant parallel lamina, and are partially burrowed. These units commonly contain planktonic foraminifera, coccoliths and organic matter (average about 5.4%, up to 13.7% total organic carbon). In addition, in-place bivalves (including thick-shelled oysters and flattened pectens) are present. The calcite-cement-rich wackestones are lighter in colour and extensively bioturbated (in most cases < 1.5% total organic carbon). This lithofacies comprises a mix of reworked skeletal fragments (including bivalves, gastropods, echinoderms, brachiopods and corals), ostracods, calcispheres, and both benthic and planktonic foraminifera that are pervasively cemented by calcite. Given the above observations, bottom waters during deposition of the Natih-B intrashelf-basinal sediments must have contained at least some oxygen, and it is unlikely that they were persistently “anoxic”. Instead, it is likely that short-term enhanced organic productivity, rapid delivery of organic components to the sediment/water interface, optimal rates of sediment accumulation and episodic burial were the fundamental parameters that controlled organic-carbon production and preservation. Organic-matter enrichment was, therefore, not restricted to anoxic depositional environments, and exploration strategies within intrashelf-basinal settings need to be expanded beyond times when basinal anoxia is thought to have existed.
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Liu, Yang, Wenru Hao, Wei He, Xia Meng, Yinlan Shen, Tao Du e Hui Wang. "Influence of Dolomite Rock Powder and Iron Tailings Powder on the Electrical Resistivity, Strength and Microstructure of Cement Pastes and Concrete". Coatings 12, n. 1 (14 gennaio 2022): 95. http://dx.doi.org/10.3390/coatings12010095.
Abstract (sommario):
Dolomite rock powder (the waste stone residue in the production of machine-made sand and stone processing) and iron tailings powder formed by mineral processing industry are solid wastes, which occupy land resources, pollute the environment and release toxic substances without reasonable processing. The dolomite rock powder and iron tailings powder composing a large number of active substances could be advantageous to the cement-based materials. In this study, the electrical resistivity of cement paste and concrete was measured. Meanwhile, the influence of dolomite rock powder and iron tailings powder on the compressive strength of concrete was investigated. The electric flux of concrete was determined to estimate the chloride ion permeability. The scanning electron microscope (SEM) and X-ray diffraction were obtained to investigate the hydration of cement paste. Results showed the electrical resistivity of all specimens presented in this order: specimens with iron tailings < specimens with dolomite rock powder < blank specimens < specimens with ground granulated blast-furnace slag (GGBS) < specimens with fly ash. The correlation between electrical resistivity and curing age of cement paste or concrete has been deduced as a quadratic function. The addition of GGBS could improve the compressive strength of concrete. Meanwhile, when the other three types of mineral admixtures were added, 5% by mass ratio of the total binder materials was the optimum for the compressive strength. The curing ages, the fly ash, the GGBS and 5% dolomite rock powder or 5% iron tailings powder demonstrated a positive effect on the chloride ion impermeability. However, when higher dosages of dolomite rock powder or iron tailings powder were added, the effect was the opposite. Finally, the compactness of the microstructure and the Ca(OH)2 of cement paste could be improved by a small dosage of dolomites or iron tailings (less than 5%).
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Torsæter, M., J. Todorovic e A. Lavrov. "Structure and debonding at cement–steel and cement–rock interfaces: Effect of geometry and materials". Construction and Building Materials 96 (ottobre 2015): 164–71. http://dx.doi.org/10.1016/j.conbuildmat.2015.08.005.
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Arjomand, Elaheh, e Terry Bennett. "Effect of casing eccentricity on cement sheath integrity". APPEA Journal 58, n. 2 (2018): 669. http://dx.doi.org/10.1071/aj17187.
Abstract (sommario):
Cement sheaths play an important role in providing zonal isolation and preventing the migration of formation fluids to aquifers and the surrounding environment. The condition of a cement sheath may change because of the imposed pressure and temperature alterations during a wellbore lifetime. Cement sheath mechanical failure may happen because of poor cement placement, development of cracks within the cement sheath and debonding at the cement sheath, casing and rock interfaces. A three-dimensional finite element framework, employing an appropriate constitutive model (Concrete Damage Plasticity, CDP) for cement sheath and a surface-based cohesive behaviour for the interfaces, is developed for integrity investigations. The incorporation of the CDP is very advantageous to model quasi-brittle materials due to its capabilities to simulate both compression and tensile damage. The effect of casing eccentricity on stress distribution within the cement sheath and the integrity of the cement sheath is investigated while enhancing the wellbore pressure. Three different degrees of casing eccentricity (30%, 50% and 70%) were considered. The huge stress concertation within the narrower part of the cement sheath makes this section susceptible to compression and tensile damage. The high magnitude of compression and tensile damage in the scenario with 70% casing eccentricity highlights the importance cement sheath centralisation.
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Tabatabaei, Maryam, Livio Santos, Ali Ahmed Al Hassan e Arash Dahi Taleghani. "Surface-Modified Graphite Nanoplatelets to Limit Deteriorative Impacts of Oil-Based Mud Residuals on Cement Bonding". SPE Drilling & Completion 00 (1 marzo 2023): 1–8. http://dx.doi.org/10.2118/210155-pa.
Abstract (sommario):
Summary Successful cementing relies on the effective removal of oil-based muds (OBMs), especially from rock and casing surfaces. However, most OBMs are heavily absorbed onto the mineral surfaces as well as casing, deteriorating the interfacial bonding of cement to these surfaces. We present a novel cement additive using graphite nanoplatelets (GNPs) to minimize the impact of mud residuals on the bonding strengths of cement. To benefit from the individual superior mechanical properties of GNPs, we develop surface modification techniques to modify their surface properties and make them compatible with the aqueous medium of cement. Surface treatment of GNPs is critical to provide a uniform dispersion of them within the cementitious matrix and also create a strong interfacial bonding between them and cement hydrates. A series of push-out tests are conducted to evaluate how the addition of surface-modified GNPs affects the bonding strength at the cement/rock interfaces corresponding to different scenarios of OBM residues. The effect of different kinds of rocks, including sandstone, limestone, and shale, is also incorporated in the push-out tests. The experimental results show that after spacer flushing for the cases of limestone and sandstone cores, treated GNPs not only limit the impact of mud residuals at the interfaces but also raise the bonding strength beyond that corresponding to water saturated cores by about 357% and 194%, respectively. For the case of shale after spacer flushing, the bonding strength recovers about 70% as compared to the water saturated cores, and this strength is about 429% higher than that measured for the water saturated case when cement is plain (without surface-modified GNPs).
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Zhu, Hai Y., Jin G. Deng, Jun Zhao, Hu Zhao, Hai L. Liu e Teng Wang. "Cementing failure of the casing-cement-rock interfaces during hydraulic fracturing". Computers and Concrete 14, n. 1 (25 luglio 2014): 91–107. http://dx.doi.org/10.12989/cac.2014.14.1.091.
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He, Xiao, Hao Chen e Xiuming Wang. "Ultrasonic leaky flexural waves in multilayered media: Cement bond detection for cased wellbores". GEOPHYSICS 79, n. 2 (1 marzo 2014): A7—A11. http://dx.doi.org/10.1190/geo2013-0361.1.
Abstract (sommario):
Good cement bond quality is significant for an oil well to prevent hydraulic communication between zones and to ensure layered exploitation. Conventional sonic logging techniques are limited to the detection region immediately behind the casing, so they can hardly be used to interpret the bonding quality between cement and rock formations. To develop a cementing evaluation method for the whole annulus, ultrasonic leaky flexural modes in radially multilayered media were investigated through finite-difference modeling. The guided waves were excited and received by pitch-catch transducers arranged in the borehole. According to the numerical results, two kinds of flexural modes were sensitive to cement debonding at different interfaces, respectively. For the primary flexural waves that arrived early and propagated all along the casing, the attenuation levels decreased due to the appearance of a fluid-filled channel between the casing and the cement sheath. The acoustic signals arriving later were the secondary flexural modes contributed by reflection echoes from the formation. They will be greatly strengthened once a debonding defect appears at the cement-formation boundary, and the arrival time of secondary flexural waves can also be applied to predict the thickness of the cement sheath. Consequently, it is possible to propose an integrated evaluation for both interfaces of the cement annulus by extracting properties of the primary and secondary flexural waves.
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Yao, Jun, Di Feng, Zhikui Wang, Chengcheng Peng, Yonggang Zhang e Lei Han. "Experimental Study on Performance of Modified Cement-Based Building Materials under High-Water-Pressure Surrounding Rock Environment". Coatings 13, n. 3 (24 febbraio 2023): 501. http://dx.doi.org/10.3390/coatings13030501.
Abstract (sommario):
Traditional cement-based grouting materials have good reinforcement and anti-seepage effects on the surrounding rock under normal conditions, but the grouting effect is not ideal due to problems such as a long setting time, a low stone ratio, and poor crack resistance under high water pressure and in a dynamic water environment. In this study, we aimed to improve the physical properties, chemical properties, and microstructure of a cement-based slurry by forming a hydrogel through its chemical crosslinking with polyvinyl alcohol and boric acid as modifiers for the purpose of improving the permeability resistance of the surrounding rock grouting under high-water-pressure conditions, which can expand the function of traditional building materials. The grouting effect of the modified cementitious material on the surrounding rock was analyzed through indoor tests, the SEM testing of the performance of the modified slurry, the numerical calculation of the seepage field, and the application of the modified slurry in combination with the actual project to verify the water-plugging effect. The research findings demonstrate that (1) the additives boric acid and PVA can significantly speed up the slurry gel time, and the gel time can be controlled within 2–20 min to meet the specification requirements. (2) At a velocity of moving water > 1 m/s, the retention of the solidified modified slurry stone body reaches more than 80%. According to the SEM analysis, the structure of the solidified modified slurry stone body is dense and has good impermeability. (3) According to the numerical calculation analysis, the modified slurry can effectively change the seepage field of the surrounding rock and improve its seepage resistance. The water pressure outside the lining is reduced by 47%, 31%, and 22%, respectively, compared with no slurry, the pure cement slurry, and cement–water-glass grouting, and the indoor test and numerical simulation conclusions are consistent.
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Teng, Jinlong, Xiaotong Yu, Ping Wang, Guoming Liu, Lingnan Cui e Xiangfei Cui. "Repairing Performance of Polymer-Modified Cement-Based Thin Spray-On Liners on Pre-Cracked Rock-like Specimens". Coatings 14, n. 2 (17 febbraio 2024): 232. http://dx.doi.org/10.3390/coatings14020232.
Abstract (sommario):
With the development of coal mining and the increase in excavation depth, the stress on roadway surrounding rock is also increasing. This creates conditions for crack development in the roadway, so it is urgent to develop rock repair materials with excellent performance. The ability of thin spray-on liner (TSL) to repair rock and concrete opens up the possibility of reusing abandoned roadways. The ability of TSL to support the surrounding rock is also important in preventing the generation of roadway waste. In this paper, styrene–acrylic emulsion (SAE), vinyl acetate–ethylene copolymer emulsion (VAE), and polyvinyl alcohol powder (PVA) were used to prepare three TSLs. Rock-like materials were configured using cement mortar according to similar principles. Three types of TSLs were tested for basic properties such as viscosity and mechanical strength, which provided data to support the explanation of the repair performance of TSLs. Three TSLs were used to repair pre-cracked rock-like specimens (PR). The number of brushing times and the angle of PR’s cracks were regarded as test variables. Changes in the mechanical strength of repaired PRs were tested by compressive and flexural tests. TSL repair performance was evaluated with the help of mechanical strength changes. Results show that polyvinyl alcohol powder modified cement-based thin spray-on liner is most suitable for repairing rock cracks; as the thickness of the brush slurry increases, its repair performance continues to improve. This paper can provide experience and a theoretical basis for the research of other rock repair materials, and it is also instructive for repairing shotcrete in the roadway.
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Liu, Kui, Deli Gao e Arash Taleghani. "Impact of Casing Eccentricity on Cement Sheath". Energies 11, n. 10 (25 settembre 2018): 2557. http://dx.doi.org/10.3390/en11102557.
Abstract (sommario):
Sustained casing pressure (SCP) in shale gas wells caused by cement sheath failure can have serious impacts on safe and efficient gas production. Considering the fact that horizontal wells are widely used for production from shale, the cementing quality and casing centricity is barely ensured in these wells. Among other indications, the casing eccentricity is identified very often in wells with SCP problems in the Sichuan field in China. Hence, the objective of this study is to analyze the effect of the casing eccentricity on the integrity of the cement sheath. To better understand stress distribution in eccentric cement sheaths, an analytical model is proposed in this paper. By comparing the results of this model with the one’s with centric casing, the impacts of the casing eccentricity on the integrity of the cement sheath is analyzed. During fracturing treatments, the casing eccentricity has a little effect on stress distribution in the cement sheath if the well is well cemented and bonded to the formation rock. However, on the contrary, the casing eccentricity may have serious effects on stress distribution if the cementing is done poorly. The debonding of casing–cement–formation interfaces can significantly increase the circumferential stress in the cement sheath. At the thin side of the cement sheath, the circumferential stress could be 2.5 times higher than the thick side. The offset magnitude of the casing eccentricity has little effect on the radial stress in the cement sheath but it can significantly increase the shear stress. We found that the risk of cement failure may be reduced by making the casing string more centralized, or increasing the thickness of the casing. The results provide insights for design practices which may lead to better integrity in shale gas wells.
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Wolterbeek, Timotheus K. T., e Suzanne J. T. Hangx. "Remediation of Annular Gas Migration along Cemented Wellbores Using Reactive Mineral Fluids: Experimental Assessment of Sodium Bicarbonate and Sodium Silicate-Based Solutions". Energies 14, n. 22 (10 novembre 2021): 7507. http://dx.doi.org/10.3390/en14227507.
Abstract (sommario):
Achieving zonal isolation along wellbores is essential for upholding the containment integrity of subsurface reservoirs and preventing fluid seepage to the environment. The sealing performance of Portland cements conventionally used to create barriers can be severely compromised by defects like fractures or micro-annuli along casing–cement–rock interfaces. A possible remediation method would be to circulate reactive fluids through compromised cement sections and induce defect clogging via mineral precipitation. We assess the sealing potential of two prospective fluids: sodium bicarbonate and sodium silicate solutions. Reactive flow-through experiments were conducted on 6-m-long cemented steel tubes, bearing ~20-μm-wide micro-annuli, at 50 °C and 0.3–6 MPa fluid pressure. For the sodium bicarbonate solution (90 g/kg-H2O), reactive flow yielded only a minor reduction in permeability, with values remaining within one order. Injection of sodium silicate solution (37.1 wt.%, SiO2:Na2O molar ratio M= 2.57) resulted in a large decrease in flow rate, effectively reaching the setup’s lower measurement limit in hours. However, this strong sealing effect can almost certainly be attributed to gelation of the fluid through polymerisation, rather than defect clogging via mineral precipitation. For both fluids investigated, the extent of solids precipitation resulting from single-phase injection was less than anticipated. This shortfall is attributed to ineffective/insufficient liberation of Ca-ions from the alkaline phases in the cement.
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Kosakowski, Georg, e Urs Berner. "The evolution of clay rock/cement interfaces in a cementitious repository for low- and intermediate level radioactive waste". Physics and Chemistry of the Earth, Parts A/B/C 64 (2013): 65–86. http://dx.doi.org/10.1016/j.pce.2013.01.003.
49
Wang, Yu, Huajian Wang, Xiaolong Zhou, Xuefeng Yi, Yonggang Xiao e Xiaoming Wei. "In Situ X-Ray CT Investigations of Meso-Damage Evolution of Cemented Waste Rock-Tailings Backfill (CWRTB) during Triaxial Deformation". Minerals 9, n. 1 (16 gennaio 2019): 52. http://dx.doi.org/10.3390/min9010052.
Abstract (sommario):
This work presents an experimental study that focused on the meso-damage evolution of cemented waste rock-tailing backfill (CWRTB) under triaxial compression using the in situ X-ray computed tomography (CT) technique. Although numerous investigations have studied the magnitude of the strength of CWRTB material, the mesoscopic damage evolution mechanisms under triaxial deformation are still poorly understood. Artificial CWRTB samples with a waste rock proportion of 30% were prepared by mixing tailings, waste rock, cement, and water. A specific self-developed loading device was used to match the CT machine to real-time CT scanning for the CWRTB sample. A series of 2D CT images were obtained by performing CT imaging at five key points throughout the test and from three positions in the sample. The CT values, for the purpose of meso-damage evolution in CWRTB, were identified. The results showed that the axial stress–strain curve presented strain hardening characteristics. The CT data revealed the inhomogeneous damage field inside the CWRTB sample and the most severely damaged regions that were usually located at the waste block-tailings paste interfaces. The changes in CT values for the different regions of interest (ROI) revealed the complicated interactions between the waste blocks and the tailings paste matrix. The meso-structural changes, formation of the localized bands, and the associated stress dilatancy phenomenon were strongly influenced by the interactions between the waste blocks and tailing paste.
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Liu, Yun-Feng, Ke Gu, Yi-Ming Shu, Xian-Lei Zhang, Xin-Xin Liu e Wen-long Mao. "Shear models and parametric analysis of the PVC geomembrane-cushion interface in a high rock-fill dam". PLOS ONE 16, n. 1 (22 gennaio 2021): e0245245. http://dx.doi.org/10.1371/journal.pone.0245245.
Abstract (sommario):
As a type of flexible impermeable material, a PVC geomembrane must be cooperatively used with cushion materials. The contact interface between a PVC geomembrane and cushion easily loses stability. In this present paper, we analyzed the shear models and parameters of the interface to study the stability. Two different cushion materials were used: the common extrusion sidewall and non-fines concrete. To simulate real working conditions, flexible silicone cushions were added under the loading plates to simulate hydraulic pressure loading, and the loading effect of flexible silicone cushions was demonstrated by measuring the actual contact areas under different normal pressures between the geomembrane and cushion using the thin-film pressure sensor. According to elastomer shear stress, there are two main types of shear stress between the PVC geomembrane and the cushion: viscous shear stress and hysteresis shear stress. The viscous shear stress between the geomembrane and the cement grout was measured using a dry, smooth concrete sample, then the precise formula parameters of the viscous shear stress and viscous friction coefficient were obtained. The hysteresis shear stress between the geomembrane and the cushion was calculated by subtracting the viscous shear stress from the total shear stress. The formula parameters of the hysteresis shear stress and hysteresis friction coefficient were calculated. The three-dimensional box-counting dimensions of the cushion surface were calculated, and the formula parameters of the hysteresis friction were positively correlated with the three-dimensional box dimensions.