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1
Feng, Yan Jun, and Xiu Wei Shi. "Hydraulic Fracturing Process: Roles of In Situ Stress and Rock Strength." Advanced Materials Research 616-618 (December 2012): 435–40. http://dx.doi.org/10.4028/www.scientific.net/amr.616-618.435.
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This paper presents results of a comprehensive study involving analytical and field experimental investigations into the factors controlling the hydraulic fracturing process. Analytical theories for fracture initiation of vertical and horizontal borehole are reviewed. The initiation and propagation process of hydraulic fracturing is performed in the field by means of hydraulic fracturing and stepwise hydraulic fracturing, the effect of factors such as in-situ stress and rock strength on fracture propagation process is studied and discussed. The fracture initiation pressures estimated from the analytical model and field experiments are compared as well as the fracturing process during case 1and case 2. Results from the analytical model and field experiments conducted in this study are interpreted with a particular effort to enlighten the factors controlling the hydraulic fracturing process.
2
Zhao, Wan Chun, Chen Wang, Ting Ting Wang, and Bing Guan. "Calculation Model Study on Damaging Stress of Hydraulically Created Fracture Propagation." Applied Mechanics and Materials 275-277 (January 2013): 238–41. http://dx.doi.org/10.4028/www.scientific.net/amm.275-277.238.
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In order to describe hydraulically created fracture propagation’s characteristics of rock matrix exactly, in this paper, establishing a stress field ‘s calculation model of fracturing propagation tip , obtaining numerical method of fracturing propagation’s characteristics based on damaging and describing fracturing propagation’s characteristics combined with method of finite element. Research shows that the corrigendum between stress field ‘s calculation model of fracturing propagation tip and practical engineering are 0.64 percent and 1.43 percent respectively. Compared with the traditional method, the result is more exactly.
3
Wang, Shuanlin, and Jianqiao Luo. "Study on the Shadow Effect of the Stress Field around a Deep-Hole Hydraulic-Fracturing Top-Cutting Borehole and Process Optimization." Processes 11, no. 2 (January 24, 2023): 367. http://dx.doi.org/10.3390/pr11020367.
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The clean utilization and green development of coal resources have become a research focus in recent years. Underground hydraulic fracturing technology in coal mines has been widely used in roof pressure relief, top coal pre-splitting, gas drainage, roadway pressure relief and goaf disaster prevention. Different in situ stress types cause great differences in the stress field around the boreholes, the critical pressure of the fracture initiation, and the direction of the fracture expansion trend; in addition, the stress shadow effect generated by the superposition of stress fields between boreholes relatively close together has a mutual coupling effect on the evolution of the stress field, the development of the plastic zone, and the crack propagation of the rock mass. Therefore, an effective method to solve the problem is to establish a mechanical model of hydraulic fracturing in boreholes for theoretical calculation, determine the influence mechanism of the crack shadow effect, and design a numerical simulation experiment of the equivalent stress fluid–solid coupling of hydraulic fracturing under different pore diameters and spacings. In addition, combining rock mechanics and fracture mechanics to analyze the influence of the shadow effect of the stress field between cracks on the evolution of the equivalent stress and the plastic zone is one of the important advances in this paper. Considering the engineering background of the site, the geological conditions and the requirements of general regulations, it is considered that the parameter selection of roof fracturing hydraulic fracturing technology in the Yushen mining area is more suitable when 0.12 m hole diameter and 3.5 m hole spacing are selected.
4
Chang, Muhsiung, and Ren-Chung Huang. "Observations of hydraulic fracturing in soils through field testing and numerical simulations." Canadian Geotechnical Journal 53, no. 2 (February 2016): 343–59. http://dx.doi.org/10.1139/cgj-2015-0193.
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Hydraulic fracturing is a potential cause of leakage of earth dams or loss of fluid in drilling and field permeability testing. The effect of hydraulic fracturing on soil grouting is also a major concern. Although hydraulic fracturing has been adopted for decades by the petroleum industry for oil recovery in rock formations, studies on fracturing in soils are relatively few and inconclusive. The aim of this study is to provide further insight into the mechanism of hydrofracturing in soils through a field grouting trial and numerical simulation. We observe hydraulic fracturing in soils during this field trial as predicted by generally accepted groutability requirements. The hydraulic fractures are found vertically developed up to the ground surface. Numerical simulations show the hydraulic fracturing is easier to be initiated in anisotropic stress conditions, where the minor principal stress is the key factor. Numerical simulations also demonstrate significant compressions and shears during injection, suggesting the mechanism of fracturing in soils would be a shearing type. Based on this study, we propose a punching and splitting mode for the hydrofracturing in soils. The equation associated with estimating fracturing pressure is verified, and the results are found to be in good agreement with the cases examined.
5
Meng, Wei, and Chuan He. "Back Analysis of the Initial Geo-Stress Field of Rock Masses in High Geo-Temperature and High Geo-Stress." Energies 13, no. 2 (January 11, 2020): 363. http://dx.doi.org/10.3390/en13020363.
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In a high geo-temperature environment, it is rarely reported that geo-temperature has been considered during a back analysis. This may cause the initial geo-stress field that is obtained by a back analysis to be wrong. In this study, according to the theory of elasticity, the theoretical solution of the hydraulic fracturing equation is obtained in a high geo-temperature environment. Since the vertical stress that is obtained by the hydraulic fracturing method is calculated using the density of overlying strata, this vertical stress lacks the thermal stress that is caused by geothermal gradients. Therefore, in a high geo-temperature environment, inverting the initial geo-stress field of rock masses directly using the stress that is measured by the hydraulic fracturing method can cause serious errors. We propose that the regression coefficient of a gravitational stress field should be set to one during a back analysis if stresses are measured by the hydraulic fracturing method, and this regression coefficient should not be equal to one if stresses are measured by overcoring methods. We also propose a workflow for the back analysis of the initial geo-stress field of rock masses that considers geo-temperature, and this workflow is applied to the Sangzhuling tunnel in China.
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Zeng, Zhengwen. "Frac-n-Flow Testing to Screen Brittle Fracture Stages in Wolfcamp Formation, Permian Basin, USA." Energies 14, no. 17 (September 1, 2021): 5450. http://dx.doi.org/10.3390/en14175450.
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A new technique, fracturing-and-flowing (frac-n-flow) testing, is introduced for horizontal drilling and multistage hydraulic fracturing (HDMHF) practitioners to check if the next stage would be a brittle fracture using the instantaneous shut-in pressure (ISIP) from the current stage. It was developed to reduce the number of not-flowing clusters in HDMHF treatments due to stress shadows in the development of tight oil reserves in Wolfcamp, Permian Basin, USA, and other similar fields. Preliminary frac-n-flow testing results show that a medium (200–1000 psi) increase in confining pressure under representative field in-situ stresses can transfer Indiana limestone from brittle fracturing to semi-ductile failing. Consequently, folds of increase (FOI) of matrix permeability vary from +13 (i.e., increase by 1300%) to −0.39 (i.e., decrease by 39%). Limestone is one of the major lithological components in Wolfcamp formation. Field ISIP data of two HDMHF wells in Wolfcamp formation show that the maximum stress shadows are +1297 psi and +1716 psi, respectively. These stress shadows might have transferred the fracturing process from brittle to semi-ductile, converting the corresponding stages from being stimulated and conductive (fracturing-n-flowing) to being damaged and not-flowing (failing-n-not-flowing). Field completion reports of the two wells confirmed that screen-out and other interruptions of operation occurred in these high stress shadowed stages.
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Lu, Cong, Li Ma, Jianchun Guo, Lin Zhao, Shiqian Xu, Bugao Chen, Yulong Zhou, Haoren Yuan, and Zhibin Tang. "Fracture Parameters Optimization and Field Application in Low-Permeability Sandstone Reservoirs under Fracturing Flooding Conditions." Processes 11, no. 1 (January 16, 2023): 285. http://dx.doi.org/10.3390/pr11010285.
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To solve engineering problems in the production process after fracturing and flooding of low-permeability sandstone reservoirs, such as rapid water-cut rise and low water flooding efficiency, a method for optimizing the fracture parameters of low-permeability sandstone reservoirs under fracturing flooding conditions was proposed. A rock property test experiment was first carried out, the fracturing coefficient was defined, and an evaluation method for the brittleness index of low-permeability sandstone was established to optimize the perforation location of the fracturing reservoir. A productivity numerical model for the two-phase flow of oil–water in matrix–fracture media was established to optimize the fracture morphology under fracturing flooding conditions. The results showed that the quartz content, Young’s modulus, and peak stress mainly affected the fracturing coefficient of rock and are the key indicators for evaluating the brittleness of low-permeability sandstone reservoirs. For production wells in the direction of minimum horizontal principal stress, the swept area of water flooding should be expanded, fracture length should be optimized to 90 m, and fracture conductivity should be 20 D·cm. For fracturing production wells in the direction of maximum horizontal principal stress, the advancing speed of the water injection front should be slowed down to reduce the risk of water channeling in injection-production wells. The optimized fracture length was 80 m, and the fracture conductivity was 25 D·cm. The application of these findings can markedly improve oil production and provide a reference for optimizing the fracture parameters of low-permeability sandstone reservoirs under fracturing flooding conditions.
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Fu, Jun Hui, Guang Cai Wen, Fu Jin Lin, Hai Tao Sun, Ri Fu Li, and Wen Bin Wu. "Coal Mine Hydraulic Fracturing Underground Drainage Research and Engineering Application." Applied Mechanics and Materials 863 (February 2017): 334–41. http://dx.doi.org/10.4028/www.scientific.net/amm.863.334.
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Using elastic mechanics and fracture mechanics, analyzing the coal seam hydraulic fracturing breakdown pressure, given its theoretical formula. According to hydraulic fracturing stress status, given the form of two typical hydraulic fracture morphology. Analyzing hydraulic fracturing highly elliptical shape. The displacement field in plane stress state is given, and the theoretical formula of fracturing radius of hydraulic fracturing is deduced. The fracturing technology of underground fracturing is presented, and the fracturing location and fracturing parameters are determined. In Sihe Coal Mine conducted fracturing test, the test results showed that: the average of drainage volume of fracturing hole improved 4.4 times compared with non-pressed-hole. The extraction compliance time is reduced by 38%. Roadway tunneling speed was improved by 15%. It can solve the problem of gas overrun in roadway excavation well, and has a good application and popularization value.
9
Feng, Jing, Qian Sheng, Chao Wen Luo, and Jing Zeng. "The Application of Hydraulic Fracturing in Storage Projects of Liquefied Petroleum Gas." Key Engineering Materials 306-308 (March 2006): 1509–14. http://dx.doi.org/10.4028/www.scientific.net/kem.306-308.1509.
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It is very important to study the pristine stress field in Civil, Mining, Petroleum engineering as well as in Geology, Geophysics, and Seismology. There are various methods of determination of in-situ stress in rock mass. However, hydraulic fracturing techniques is the most convenient method to determine and interpret the test results. Based on an hydraulic fracturing stress measurement campaign at an underground liquefied petroleum gas storage project which locates in ZhuHai, China, this paper briefly describes the various uses of stress measurement, details of hydraulic fracturing test system, test procedure adopted and the concept of hydraulic fracturing in arriving at the in-situ stresses of the rock mass.
10
Zhang, Zuxun, Hongtu Wang, Bozhi Deng, Minghui Li, and Dongming Zhang. "Field Investigation of Hydraulic Fracturing in Coal Seams and Its Enhancement for Methane Extraction in the Southeast Sichuan Basin, China." Energies 11, no. 12 (December 10, 2018): 3451. http://dx.doi.org/10.3390/en11123451.
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Hydraulic fracturing is an effective technology for enhancing the extraction of reservoir methane, as proved by field experience and laboratory experiments. However, unlike conventional reservoirs, coal seams had high stress sensitivity and high anisotropy. Therefore, the efficiency of hydraulic fracturing in coal seams needs to be investigated. In this study, hydraulic fracturing was performed at Nantong mine in the southeast Sichuan basin, China. The field investigation indicated that the hydraulic fracturing could significantly enhance the methane extraction rate of boreholes ten times higher than that of normal boreholes in one of the minable coal seams (named #5 coal seam). The performance of hydraulic fracturing in three districts revealed that compared with south flank, the fluid pressure was higher and the injection rate was lower in north flank. The methane extraction rate of south flank was inferior to that of north flank. It indicated hydraulic fracturing had less effect on #5 coal seam in south flank. Moreover, the injection of high-pressure water in coal seams could also drive methane away from boreholes. The methane extraction rate of the test boreholes demonstrated the existence of methane enrichment circles after hydraulic fracturing. It indicated that hydraulic fracturing did act on #5 coal seam in south flank. However, due to the high stress sensitivity of coal seams and the high geo-stress of south flank, the induced artificial fractures in #5 coal seam might close with the decline of the fluid pressure that led to a sharp decline of the methane extraction rate.
11
Li, Jun, Xueli Guo, Gonghui Liu, Shuoqiong Liu, and Yan Xi. "New Analytical Method to Evaluate Casing Integrity during Hydraulic Fracturing of Shale Gas Wells." Shock and Vibration 2019 (April 24, 2019): 1–19. http://dx.doi.org/10.1155/2019/4253241.
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An accurate analysis of casing stress distribution and its variation regularities present several challenges during hydraulic fracturing of shale gas wells. In this paper, a new analytical mechanical-thermal coupling method was provided to evaluate casing stress. For this new method, the casing, cement sheath, and formation (CCF) system was divided into three parts such as initial stress field, wellbore disturbance field, and thermal stress field to simulate the processes of drilling, casing, cementing, and fracturing. The analytical results reached a good agreement with a numerical approach and were in-line with the actual boundary condition of shale gas wells. Based on this new model, the parametric sensitivity analyses of casing stress such as mechanical and geometry properties, operation parameters, and geostress were conducted during multifracturing. Conclusions were drawn from the comparison between new and existing models. The results indicated that the existing model underestimated casing stress under the conditions of the geostress heterogeneity index at the range of 0.5–2.25, the fracturing pressure larger than 25 MPa, and a formation with large elastic modulus or small Poisson’s ratio. The casing stress increased dramatically with the increase of in situ stress nonuniformity degree. The stress decreased first and then increased with the increase of fracturing pressure. Thicker casing, higher fluid temperature, and cement sheath with small modulus, large Poisson’s ratio, and thinner wall were effective to decrease the casing stress. This new method was able to accurately predict casing stress, which can become an alternative approach of casing integrity evaluation for shale gas wells.
12
Liu, Xiaoqiang, Zhanqing Qu, Tiankui Guo, and Wenjie Huang. "Numerical simulation of stress field distribution before re-fracturing treatment." IOP Conference Series: Earth and Environmental Science 814, no. 1 (July 1, 2021): 012008. http://dx.doi.org/10.1088/1755-1315/814/1/012008.
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Zhang, Yongjiang, Benqing Yuan, and Xingang Niu. "Response Characteristics of Coal-Like Material Subjected to Repeated Hydraulic Fracturing: An Evaluation Based on Real-Time Monitoring of Water Injection Pressure and Roof Stress Distribution." Shock and Vibration 2021 (May 27, 2021): 1–10. http://dx.doi.org/10.1155/2021/9931137.
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Conventional hydraulic fracturing has several disadvantages, including a short effective extraction time and low fracture conductivity during long-term extraction. Aiming at overcoming these shortcomings, a similar simulation test of repeated hydraulic fracturing was conducted in this study, and the evolutionary rules regarding the injection water pressure and stress distribution of the coal seam roof during this repeated hydraulic fracturing were revealed. The research results show that after multiple hydraulic fracturing, the number of cracks in the coal seam and the range of fracturing influence have increased significantly. As the number of fracturing increases, the initial pressure required for cracking decreases. The highest water injection pressure of the first fracturing was 2.8 MPa, while the highest water injection pressures of the second and third fracturing were 2.7 MPa and 2.4 MPa, respectively. As the number of fracturing increases, the area of increased stress will continue to expand. After the first fracturing, the impact radius of fracturing is 100 cm. After the second fracturing, the radius of influence of fracturing expanded to 150 cm. When the third fracturing was over, the radius of influence of the fracturing expanded to approximately 250 cm. It can be seen that, compared with conventional hydraulic fracturing, repeated hydraulic fracturing shows better fracturing effect. The research results can be used as a basis for repeated hydraulic fracturing field tests to increase coal seam permeability.
14
Skulkin, Alexander A. "EXPERIMENTAL DETERMINATION OF STRESS PARAMETERS IN THE MINING FIELD." Interexpo GEO-Siberia 2, no. 4 (May 21, 2021): 123–29. http://dx.doi.org/10.33764/2618-981x-2021-2-4-123-129.
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The experience of measuring the stress state of the rock mass at the Tashtagol iron ore deposit and the result of stresses acting in the induced field in the vicinity of 10 orts at a depth of 800 m from the daily surface (horizon -350) is presented using the method of measuring hydraulic fracturing. Stress concentration zones around the mine are determined at the measuring station.
15
Alfat, Sayahdin, Masato Kimura, and Alifian Mahardhika Maulana. "Phase Field Models for Thermal Fracturing and Their Variational Structures." Materials 15, no. 7 (March 31, 2022): 2571. http://dx.doi.org/10.3390/ma15072571.
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It is often observed that thermal stress enhances crack propagation in materials, and, conversely, crack propagation can contribute to temperature shifts in materials. In this study, we first consider the thermoelasticity model proposed by M. A. Biot and study its energy dissipation property. The Biot thermoelasticity model takes into account the following effects. Thermal expansion and contraction are caused by temperature changes, and, conversely, temperatures decrease in expanding areas but increase in contracting areas. In addition, we examine its thermomechanical properties through several numerical examples and observe that the stress near a singular point is enhanced by the thermoelastic effect. In the second part, we propose two crack propagation models under thermal stress by coupling a phase field model for crack propagation and the Biot thermoelasticity model and show their variational structures. In our numerical experiments, we investigate how thermal coupling affects the crack speed and shape. In particular, we observe that the lowest temperature appears near the crack tip, and the crack propagation is accelerated by the enhanced thermal stress.
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Qi, Fuzhou, Zhanguo Ma, Dangwei Yang, Ning Li, Bin Li, Zhiliu Wang, and Weixia Ma. "Stability Control Mechanism of High-Stress Roadway Surrounding Rock by Roof Fracturing and Rock Mass Filling." Advances in Civil Engineering 2021 (February 28, 2021): 1–17. http://dx.doi.org/10.1155/2021/6658317.
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Large deformation of roadway and coal bump failures have always been the focus in deep underground engineering. By considering the Lu’an mining district in China, the failure mode and stability improvement process of high-stress roadways were analysed with the field tests and numerical simulations. The field test results showed that a great amount of deformation and serious damage occurred in surrounding rocks during panel retreat due to the suspended roof. A novel approach employing roof fracturing and collapsed rock filling effect was adopted to maintain the roadway stability. A numerical model was established with the Universal Distinct Element Code (UDEC) to research the fracturing characteristics between the roadway and gob roofs and the stress change in the surrounding rock. The modelling results demonstrated that, without fracturing roof, the peak vertical stress of the coal pillar was 18.3 MPa and the peak vertical stress of the virgin coal rib was 15.6 MPa. The roadway was in a state of high stress. With fracturing roof, the peak vertical stress of coal pillar was 9.3 MPa and the peak vertical stress of virgin coal rib was 13.4 MPa. The fractured rock mass in the gob expanded in volume and provided supporting resistance to the overlying strata, which relieved stress concentrations in the coal pillar. Field measurement results indicated that the roadway large deformation was successfully resolved during excavation and panel retreat after implementing the novel approach, providing useful references for the application of this novel approach in similar coal mines.
17
Zhang, Yan Xin, Chang Sheng Song, and Jian Hui Zhao. "Study on Hydraulic Fracturing Method for In Situ Stress Measurement in Deep Boreholes." Applied Mechanics and Materials 741 (March 2015): 567–71. http://dx.doi.org/10.4028/www.scientific.net/amm.741.567.
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Information of in situ stress field is crucial for predicting the response of rock masses to the disturbance associated with underground constructions. Hydraulic fracturing is an efficient method for determining the stress field and is suitable at the early stages of projects when no underground access exists. For this, a series of new improved techniques and equipments are developed for the deep boreholes to increase the reliability of system. For a better understanding of the stress test, the ideal HF pressure-time curve is given and the fracturing procedure is analyzed. Based on the theory of HF stress calculation, two implicit inequations are deduced.
18
Pan, Chao, Yu Jun Zuo, Shang Gao, and Wei Li. "Numerical Simulation on Hard and Stable Roof Control by Means of Directional Hydraulic Fracturing in Coal Mine." Applied Mechanics and Materials 638-640 (September 2014): 894–97. http://dx.doi.org/10.4028/www.scientific.net/amm.638-640.894.
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Hydraulic fracturing is a method which combines a natural action with a factitious means to alter rock structure. In order to control the extending direction of fracture in the process of hydraulic fracturing, directional hydraulic fracturing is necessary. According to fracture initiation and extension mechanism, taking fully into account the flow-stress-damage coupling effect, simulating with numerical way and analyzing a law of the roof under the dynamic failure process on a working face with a hard and stable roof in 2 cases, the one is the non-directional directional hydraulic fracturing, and the other one is wedge groove directional hydraulic fracturing by RFPA2D-Flow. Based on analyzing the distribution law of the primary stress field on roof surrounding rock, we reveal the control mechanism and behavior law of directed by wedge groove directional fracturing. The study results shows that: First, under the coupling effect from the high hydraulic pressure and crustal stress, failure of roof is not simply a shearing failure, but a compound stress effect from tensile and compress failure which tension contributes more. Second, the directional fracturing by wedge-groove guides to the main fracture progressing into directional expansion, relying on man-made weak plane, it also makes the roof directional hierarchically, timely and fractionated carving come true.
19
Wu, Xinhua, Tao Zhu, Yufei Liu, Guoyu Zhang, Guanghui Zheng, and Fengnian Wang. "Mechanism of Coal Seam Permeability Enhancement and Gas Outburst Prevention under Hydraulic Fracturing Technology." Geofluids 2022 (March 22, 2022): 1–9. http://dx.doi.org/10.1155/2022/7151851.
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In view of the high gas pressure and low permeability of deep coal seam, it is difficult to control gas, which affects the safety production of coal mine. The technical scheme of hydraulic fracturing to improve the permeability of coal seam is put forward, and the gas drainage technology is used to control the gas emission of coal seam. The fracturing effect under different water pressure, different gradient fracturing times, and in situ stress is analyzed by using 3DEC (3-Dimensional Distinct Element Code) discrete element software. The simulation analysis and field verification results show that the coal seam gas pressure increases linearly with the buried depth. In situ stress characteristics and hydraulic strength are the key factors affecting the effect of hydraulic fracturing. The fracturing radius increases with the increase of flow. When the construction pressure of hydraulic fracturing test is 18 MPa, the distance between fracturing hole and drainage hole is 8.5 m. The actual measurement shows that after hydraulic fracturing and gas drainage, the maximum gas emission is reduced by 51%, and the average gas emission is reduced by 58%.
20
Chen, Xue Xi, Rui Qing Bi, Wen Guang Jin, and Yong Xu. "Permeability Improvement Technology of Directional Hydraulic Fracturing in Low Permeability." Applied Mechanics and Materials 599-601 (August 2014): 385–90. http://dx.doi.org/10.4028/www.scientific.net/amm.599-601.385.
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According to the conventional fracturing could easily lead to the local stress concentration of coal, the effect of pressure relief and permeability improvement is not ideal. The mechanism of directional hydraulic fracturing is analyzed and the parameters such as the layout of directional hole, the fracturing hole sealing, the minimum cracking pressure are discussed, then the field application tests are carried out. The results show that the directional hydraulic fracturing effect is better than that of ordinary fracturing hole and the maximum concentration and the average drainage scalar is respectively 3.75 times and 4 times of the ordinary hole pumping gas fracturing effects. The effect of permeability improvement is remarkable.
21
Zhang, Peng, Zhenghua Wu, Shuying Hu, Jikai Wei, Manlai Zhang, Zhengqin Ye, Chunsheng Pu, and Jingyang Pu. "Stress Characteristics near Wellbore and Prevention Casing Deformation for Fracturing Horizontal Wells." Geofluids 2022 (December 30, 2022): 1–12. http://dx.doi.org/10.1155/2022/3034970.
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Aiming at the problem that casing deformation can easily occur in tight oil horizontal well fracturing, based on the rock mechanics experiments and probability statistics, the distribution characteristics and law of the near-wellbore stress field of the reservoir in STH M56 were solved and analyzed by using the finite element modeling numerical method. The research shows that (1) the max/min horizontal stress ratio of the M56 tight oil reservoir is 1.2, the difference is less than 8 MPa, and this characteristic condition is more conducive to the formation of complex fracturing network in the reservoir during fracturing. (2) In M56, the Mises stress isoline near the borehole is symmetrically distributed. Stress concentration has four dangerous points (30°, 150°, 210° and 330°); a sector-shaped high dangerous stress zone is formed along the four dangerous points. As the pumping pressure increases, the vertical Mises stress first increases and then decreases, while the horizontal Mises stress first decreases and then increases. The max-Mises stress at the casing wall is linearly and positively correlated with the stress uniformity coefficient. When the pumping pressure is 80 MPa, the Mises stress exceeds the safe pressure limit of the casing. A pumping pressure of 70 MPa fracturing is the safe pumping pressure for the reservoir casing. (3) It is found that the 90° and 270° horizontal fixed plane perforations can avoid the dangerous stress zone, increasing and decreasing the injection flow rate of the fracturing pump step by step ( step pressure ≤ 5 MPa ) at the start and stop stages of fracturing; the control of the pump pressure during the whole process of fracturing is within 70 MPa, which can prevent the casing deformation.
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Guo, Wei, Wei Ju, Majia Zheng, Weijun Shen, Jian Zhang, Pingping Liang, Shengyu Wang, and Haohao Hu. "Present-Day In Situ Stress Analysis in Shale Reservoir of Haiba Block, Southern Sichuan Basin, South China." Geofluids 2023 (February 22, 2023): 1–11. http://dx.doi.org/10.1155/2023/3249570.
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Natural gas from shale gas reservoirs has been an important contributor for reserve growth, deliverability construction, and profits growth in natural gas industry in the world. Hydraulic fracturing is commonly required in the shale gas commercial development, and thus understanding the present-day in situ stress field is greatly significant for the hydraulic fracturing and efficient development in shale gas reservoirs. However, there are no systematic investigations on the present-day in situ stress field in the Haiba Block from the Sichuan Basin, South China. In this study, the present-day in situ stress orientations and magnitudes in shale reservoir of Haiba Block are investigated based on the well interpretations from borehole image log and geomechanical modeling. Then, the effects of stresses on hydraulic fracturing, horizontal wells, and natural fracture reactivation were discussed. The results indicate that the horizontal maximum principal stress (SHmax) orientation is mainly in the NE-SW-trending, NW-SE-trending, and WNW-ESE-trending in the Haiba Block. The magnitudes of horizontal maximum and minimum principal stresses are 13.5 MPa~85.5 MPa and 2.8 MPa~31.6 MPa, respectively. In the Haiba Block, the differential stress is generally low in the northern part, which indicates that complex hydraulic fracture networks may be produced. While the natural fractures are generally stable under the present-day in situ stress field. When the increase of pore pressure gradient is about 30 KPa/m, nearly all natural fractures in the Longmaxi Formation may be reactivated. The results can provide the insights into a better understanding of the present-day in situ stress distribution so as to optimize perforation orientation, hydraulic fracturing design, and enhance gas production in shale gas reservoirs.
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Tiejun, Lin, Li Zhaoyang, Zhao Zhaoyang, Bao Xiaomin, and Zhang Qiang. "Failure analysis of long round thread in horizontal well casing under multi-axis loading." E3S Web of Conferences 165 (2020): 01007. http://dx.doi.org/10.1051/e3sconf/202016501007.
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The casing is subjected to complicated forces underground, and the threaded joint of the casing is the weak link of the casing. becoming more and more severe, various kinds of failure accidents often occur in practical use. Therefore, in view of the casing thread fracture failure during the process of volumetric fracturing in well W of an oil field. The finite element model of 5-1/2"API casing long round threaded joint was established in this paper, ABAQUS software was used to simulate and analyze the stress and deformation of casing thread under the loading state of overlock, axial tension and pressure, and fracturing internal pressure. The results show that the stress distribution of teeth is reasonable. Under the condition of axial tension and compression, the maximum stress of casing thread exceeds the yield strength into plasticity and causes damage. However, when fracturing and stimulation technology is implemented, the stress of the collar and casing body increases significantly, and the fracture is caused by fatigue and extended fracture under the alternating fracturing load. The finite element analysis results are consistent with the field failure results. Study the influence of downhole complex working condition on casing thread by simulation, which is of great significance to the protective casing.
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Lin, Hai, Yakai Tian, Zhenwei Sun, and Fujian Zhou. "Fracture Interference and Refracturing of Horizontal Wells." Processes 10, no. 5 (May 2, 2022): 899. http://dx.doi.org/10.3390/pr10050899.
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Due to fracture interference, not all perforations can be fractured, resulting in 20% of fractures contributing to 80% of the total production. The extraction of oil and gas also reduces production, necessitating refracturing. In this study, the finite element method was used to simulate multiple fractures fracturing simultaneously and the stress field distribution was then extracted and applied to a new geological model. This paper explains the effect of stress around the horizontal wellbore on new fractures during the refracturing of old wells using a temporary plugging technique. The results show that initial breaking pressures are the same, but as fractures extend, inter-fracture interference increases, resulting in different fracture extension pressures and widths. The fracturing fluid is filtered into the reservoir matrix after fracturing, reducing formation stress. Compared with fracturing at the initial fracture site, reperforating fracturing has a lower fracture extension pressure and a longer fracture length. According to this study, hydraulic fractures have a 15 m effective influence radius on the external formation. Stress relief is beneficial for fracture initiation prior to refracturing. Reperforating and fracturing, in combination with temporary plugging technology, can assist in increasing the effective stimulated reservoir volume and achieving high and stable production.
25
Zhai, Wen, Yachao Guo, Xiaochuan Ma, Nailv Li, Peng Zhang, Kun Ma, Yuanxin Jing, Hong Yu, and Xiaotong Li. "Research on Hydraulic Fracturing Pressure Relief Technology in the Deep High-Stress Roadway for Surrounding Rock Control." Advances in Civil Engineering 2021 (October 25, 2021): 1–13. http://dx.doi.org/10.1155/2021/1217895.
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With the increase of mining depth in underground engineering, deep ground pressure has an extremely unfavorable impact on safety production and the economic benefits of coal mines and the control of the roadway stability in deep mines are gradually highlighted. In this study, the working face 14203 of the Zaoquan coal mine was taken as the engineering background, the deformation mechanism of surrounding rock in the deep-buried high-stress roadway was analyzed, and the hydraulic fracturing pressure relief technology in the advanced roadway was proposed for surrounding rock control. Finally, the numerical simulation and field tests were used to validate the comprehensive effect of the proposed technology. Without damaging the roadway stability in the working face, the hydraulic fracturing pressure relief technology can optimize the stress environment and stability of the roadway through the artificial control of the roof fracture position. The numerical simulation shows that under the action of hydraulic fracturing, the cutting slot is formed, the deformation and failure mode of the roof are changed, the stress of surrounding rock is reduced, and the development of the plastic zone of surrounding rock is limited. As a result, the stability of surrounding rock in the roadway is effectively protected. The field test shows that after the adoption of hydraulic fracturing pressure relief technology, the roof subsidence, floor separation, bolt stress, and cable stress decrease, and the deformation of surrounding rock is reduced significantly. Therefore, hydraulic fracturing pressure relief technology is verified as an effective method to control the large deformation of the surrounding rock in the deep-buried roadway.
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Hu, Xinyu, Runxu Zhang, Bailin Zhang, Xinghua Zhang, Lulu Zhang, Yongdan Yang, and Fazhi Yan. "A Study on the Factors Influencing Coal Fracturing Range Caused by Liquid Carbon Dioxide Phase Transition." Geofluids 2022 (May 24, 2022): 1–12. http://dx.doi.org/10.1155/2022/4754764.
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Liquid carbon dioxide phase transition fracturing technology (LCPTF) is an effective method to increase coal seam permeability, but there are many factors that affect the fracturing effect. Blasting pressure, vent diameter, and blasting time are important factors that affect the fracturing effect. However, very limited studies were performed in this regard. Therefore, in this paper, a multifield coupled model for fracturing coal bodies by LCPTF is established; the effect of blasting pressure, vent diameter, and blasting time on blasting effectiveness was studied; a numerical simulation study based on the seepage field and stress field is performed and verified in the field based on the specific geological conditions of Hujiahe mine. Experimental results show that the fracturing radius and the maximum displacement of coal increase with the increase of blasting pressure, and the fracturing radius is 4.875 m when the blasting pressure is 280 MPa, which is 9.6% higher than that of 200 MPa, and the effect is obvious. The fracturing effect improves with the increase of vent diameter but the effect is modest. In general, the fracturing effect increases with the increase of CO2 impact duration, and when there is no gas impact, the fracturing radius basically remains the same. The maximum displacement gradually decreases with time, and its maximum displacement of the coal body decreases by 33.69% at 200 s. After field blasting, the gas flow attenuation coefficient was reduced by up to 85.7% and the effective radius of influence was between 4 and 5 m.
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Liu, Guang Feng, Yang Lu, Ling Lu, and Jun Tao Wang. "Ultralow Permeability Reservoir Stress Field Simulation." Advanced Materials Research 816-817 (September 2013): 728–33. http://dx.doi.org/10.4028/www.scientific.net/amr.816-817.728.
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The simulation method of reservoir tectonic and present stress field was recommended, and in-situ stress distribution of C82 ultralow permeability reservoir formation in Changqing oilfied Z19 well block was computed. The method is based on finite element analysis, of which the contents and procedures include geological model establishment, calculation model establishment and results analysis. The simulation precision depends on the reliability of models. Inversion criteria need to be set to determine whether the ultimate simulating result is reasonable. Main inversion criteria include absolute inversion, principle stress criteria, deformation criteria, etc. The maximum principle stress value of C82 formation in Z19 well block is between 35.7 and 45.2MPa, whose direction is NE 72o-80o, and the dominant direction is NE 75o. The differential stress value is between 0.4 and 9.8MPa. The relationship between stress, reservoir parameters and production data was discussed. The simulation results can be taken as reference for well pattern design, optimization and overall fracturing design.
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Liu, Mengxuan. "Research on fracture trend of repeated fracturing." Journal of Physics: Conference Series 2247, no. 1 (April 1, 2022): 012016. http://dx.doi.org/10.1088/1742-6596/2247/1/012016.
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Abstract The fracture trend of repeated fracturing is directly related to the effect of repeated fracturing and whether it can effectively expand the swept volume. In this paper, a large-scale hydraulic fracturing process simulation device is used to conduct laboratory experiments on fractured reservoirs to study the initiation and extension of repeated fracturing fractures under different stress states. The experimental results show that new fractures are easy to extend from the natural fractures near the wellbore, and the initiation pressure of the secondary fracturing is reduced due to the inducing effect of the initial fractures. The conclusion has a certain guiding function for the prediction of repeated fracturing fracture propagation in field fractured reservoirs, and it is of great significance for fracturing construction.
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Chen, Yi, Zhihong Kang, Yuzhu Kang, Xiaocheng Chen, Xiaohong Chen, Qingteng Fan, Yukun Du, and Jinguang Wang. "A Thermal-Fluid-Solid Coupling Computation Model of Initiation Pressure Using Supercritical Carbon Dioxide Fracturing." Processes 11, no. 2 (February 1, 2023): 437. http://dx.doi.org/10.3390/pr11020437.
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With the characteristics of low fracturing pressure, little damage to the reservoirs, and assuming the role of carbon storage, supercritical carbon dioxide (SC-CO2) fracturing is suitable for the development of unconventional oil and gas resources. Based on the tensile failure mechanism of rocks, this paper establishes a thermal-fluid-solid coupling initiation pressure model for SC-CO2 fracturing. Using this model, the changes in formation temperature and pore pressure near a wellbore caused by invasion of CO2 into the formation are analyzed, as well as the impact of these changes on the tangential stress of reservoir rocks. The field data of SC-CO2 fracturing in a sandstone gas well are used to validate the reliability of the model. The results show that SC-CO2 fracturing can significantly reduce the initiation pressure, which decreases with the increase in fracturing fluid injection rate. The minimum value of tangential stress is located at the well wall, and the direction of tangential stress caused by formation temperature and pore pressure is opposite, with the former greater than the latter. The increase in Poisson’s ratio, the increase in elastic modulus and the decrease in bottom hole temperature can reduce the initial fracturing pressure of the reservoir. The computation model established in this paper provides an effective method for understanding the reservoir fracturing mechanism under the condition of SC-CO2 invasion.
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Gao, Guiyun, Chenghu Wang, Hao Zhou, and Pu Wang. "Modified Fracture Mechanics Approach for Hydraulic Fracturing Stress Measurements." Geofluids 2020 (December 3, 2020): 1–11. http://dx.doi.org/10.1155/2020/8860163.
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Hydraulic fracturing (HF) test has been widely used to determine in situ stress. The use of a conventional continuum method for this purpose has raised considerable controversies concerning field tests, particularly in the determination of the maximum horizontal principal stress under preexisting fractures. Fracture mechanics methods are very promising when considering preexisting cracks. However, most fracture mechanics methods do not include the effects of confinement on fracture parameters that depend on confining stress. In the present paper, we proposed a modified approach based on fracture mechanics for stress determination considering the relation between fracture toughness and confining stress based on the Rummel and Abou-Sayed methods. Then, we conducted true triaxial hydraulic fracturing tests under different stress ratios for granite and sandstone specimens to verify the proposed approach. The observed typical pressure-time curves indicate that in the conducted hydraulic fracturing tests, the steady fracture growth was attained. Moreover, we demonstrated that the stress ratios influence crack orientations. The horizontal maximum principal stresses determined using the modified Rummel method achieve the lowest relative error compared with other considered stress estimation approaches. This modified fracture mechanics method could be used as a potential alternative approach to obtain a considerably more precise estimation of the maximum horizontal stress in hydraulic fracturing stress determination.
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Patutin, AV, and SV Serdyukov. "Laboratory stands for hydraulic fracturing simulation in a nonuniform stress field." IOP Conference Series: Earth and Environmental Science 991, no. 1 (February 1, 2022): 012035. http://dx.doi.org/10.1088/1755-1315/991/1/012035.
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Abstract The paper considers the capabilities of well-known laboratory facilities for hydraulic fracturing modeling under the true triaxial loading conditions. Of greatest interest are the stands that allow you to create a crack in large cubic samples with an edge length of 200 mm or more. In this case, it is possible to reduce the influence of edge effects from the boundaries of the sample on the propagation path of the discontinuity. The review includes research results obtained using 10 different facilities located in major scientific centers.
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Guan, Bing, Shibin Li, Jiran Liu, Ligang Zhang, and Shuangqing Chen. "Analysis and optimization of multiple factors influencing fracturing induced stress field." Journal of Petroleum Exploration and Production Technology 10, no. 1 (July 25, 2019): 171–81. http://dx.doi.org/10.1007/s13202-019-0729-3.
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Wang, Hongjian, Wanlin Gong, Guangxiang Yuan, Xiaodong Wang, Jitao Zhao, Yujie Su, and Yuchen Wang. "Effect of In-Situ Stress on Hydraulic Fracturing of Tight Sandstone Based on Discrete Element Method." Energies 15, no. 15 (August 3, 2022): 5620. http://dx.doi.org/10.3390/en15155620.
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The tight sandstone reservoir in the Qianfoya formation of well PL-3 of the Puguang gas field in Sichuan, China, obtained a high-yield gas flow after a volume fracturing treatment. However, the stimulated reservoir volume (SRV), fracture morphology, scale and formation law still remain unclear. Based on particle flow discrete-element theory in this paper, we carried out a few trials of the Brazilian splitting test, uniaxial compression and triaxial compression of rock mechanics. Meanwhile, the research also testified to the conversion relationship between macroparameters and microparameters, established the numerical simulation on hydraulic fracturing through PFC2D discrete element software, and finally analyzed the influence of difference coefficients on the fracturing effect, in terms of different in-situ stresses. The conclusions are as follows: firstly, the influence of in-situ stress is essential for the direction, shape and quantity of fracture propagation, and the fractures generated by hydraulic fracturing are mainly tension fractures, accounting for over 90% of the total longitudinal fractures. Secondly, it is indicated that when the difference coefficient is small in the in-situ stress, the fractures formed by hydraulic fracturing expand randomly around the wellbore. When the difference coefficient Kh of in-situ stress is above 0.6, the development of hydraulic fractures is mainly controlled by in-situ stress; as a result, the fractures tend to expand in the vertical direction of the minimum horizontal principal stress and the fracture shape is relatively singular. When the difference coefficient of in-situ stress was 0.3, in total, 3121 fractures were generated by fracturing, and the fractal dimension D value of the fracture network complexity was 1.60. In this case, this fracturing effect was the best and it is the easiest to achieve for the purpose of economical and effective development on large-scale volume fracturing.
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Safari, Reza, Raju Gandikota, Ovunc Mutlu, Missy Ji, Jonathan Glanville, and Hazim Abass. "Pulse Fracturing in Shale Reservoirs: Geomechanical Aspects, Ductile/Brittle Transition, and Field Implications." SPE Journal 20, no. 06 (December 18, 2015): 1287–304. http://dx.doi.org/10.2118/168759-pa.
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Summary This paper presents a brief review of misconceptions on industry-standard brittleness/ductility definitions; geomechanical aspects and numerical evaluation of pulse fracturing by use of an advanced constitutive model implemented within the ANSYS® Autodyn® (ANSYS 2014); and fracture-network patterns because of pulse loading in shale that show ductile/brittle transition. In shale gas, one of the primary goals is to create extensive fracture networks that can remain open during production. Field experience has shown that not all shale formations respond to hydraulic fracturing effectively. It is important to identify and accurately design alternative fracturing techniques that would overcome some of the limitations. Pulse-fracturing rates and peak loads can be customized to lie between hydraulic and explosive fracturing. This technique has the potential to shatter shale, in particular by triggering a ductile/brittle transition at an optimized pulse rate. To date, operational considerations of pulse fracturing for success remain qualitative. Recent advances in computational geomechanics help us quantify the effect of key operational parameters for field applications. Further to this, advanced constitutive models implemented for these analyses have the benefit of simulating ductile/brittle transition, if the stress state and loading conditions dictate that the material should. This study on pulse fracturing shows that for a certain combination of reservoir, geomechanical, and pulse-loading parameters, induced fractures can propagate in multiple directions. This phenomenon might promote a self-propping mechanism for a network of fractures. At the end of this paper, favorable conditions when the pulse-fracturing technique would work and key parameters that trigger ductile/brittle transition are summarized and presented.
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Zhao, Wan Chun, Ting Ting Wang, Chen Yan Sun, Ying Liu, and Cai Ping Yang. "Study on Linear Calculation Method for the Refracturing Total Stress Field." Applied Mechanics and Materials 166-169 (May 2012): 3052–55. http://dx.doi.org/10.4028/www.scientific.net/amm.166-169.3052.
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In order to accurately describe the impact is on the redirection of the secondary fracturing caused by stress field distribution of the reservoir , according to the superposition principle of the potential, builds the pore pressure induced model around refracturing wells ; introduces the fluid influence factor coefficient , builds initial artificial crack induced stress field model. Finally, the three stress applies the linear superposition principle .Obtaining the total stress field before the refracturing , provides a reliable theoretical calculation basis for the induced stress calculation
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Yang, Shang Yu, Jian Jun Wang, Guang Xi Liu, and Li Hong Han. "Horizontal well of Shale Gas Complex Fracturing Casing Failure Mechanism." Materials Science Forum 944 (January 2019): 898–902. http://dx.doi.org/10.4028/www.scientific.net/msf.944.898.
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Shale gas well casing deformation failure is extremely serious in complex fracturing process. Based on the elastic mechanics theory, the distribution law of casing’s maximum equivalent stress field with the non uniform external extrusion is calculated by the complex variable function method. Meanwhile, casing deformation failure mechanism with non uniform external extrusion is revealed. For another, the maximum equivalent stress of the casing is analyzed with the case of a/b=2 and a/b=5. The result shows that the unevenness of the extrusion load has a great influence on the casing maximum equivalent stress distribution. The findings provide technical support for casing design and selection in complex fracturing process of shale gas well. Keywords: shale gas well; complex fracturing; casing formation; failure mechanism
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Safari, Reza, Richard Lewis, Xiaodan Ma, Uno Mutlu, and Ahmad Ghassemi. "Infill-Well Fracturing Optimization in Tightly Spaced Horizontal Wells." SPE Journal 22, no. 02 (November 14, 2016): 582–95. http://dx.doi.org/10.2118/178513-pa.
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Summary Cost-effective production from unconventional reservoirs relies on creating new reservoir surface area where fractures are extended into and produce from undepleted zones. Field observations indicate that infill-well fractures could propagate toward nearby producers and depleted zones. This communication between infill and producer wells has been seen to cause casing collapse, and negatively affect current production levels. In this paper, an integrated reservoir/geomechanics/fracture work flow is established to optimize infill-well treatment schedule and to minimize fracture communication between wells. In particular, the paper presents: (i) numerical evaluation of depletion-induced stress changes between tightly spaced producers, (ii) hydraulic-fracture curving in a perturbed stress field, and (iii) hydraulic-fracture communication between wells, and infill-well treatment-design optimization to maximize production. A systematic study of depletion effects and the key parameters that control fracture curving allows us to improve the infill-well fracture design by minimizing the communication between wells while maximizing the hydraulic-fracture extent. Depletion perturbs the in-situ stress tensor in the formation around fractured horizontal wells. The analysis shows that the perturbed-stress field is a function of stress/formation anisotropy, fluid mobility, pore pressure, operating bottomhole pressure (BHP), and Biot's constant. A fracture-propagation model, coupled with the altered in-situ stress field, is used to predict the hydraulic-fracture propagation path(s) and their radius of curvature (i.e., if the stress state dictates that the fractures should curve). The analyses are performed for different infill-well treatment schedule(s), and yield the most-likely fracture geometries (taking into account uncertainties in a shale formation). Resulting infill-well fracture geometries are imported into a reservoir simulator to quantify the production and to identify the optimal design parameters. The coupled work flow (reservoir/geomechanics/fracture) is then applied to a field example to demonstrate the feasibility of its application at the reservoir scale. The results show that (a) infill-well fractures between tightly spaced horizontal wells can intentionally be curved and (b) communication between wells and fracture-coverage area can be controlled by adjusting stimulation parameters to maximize recovery. Forward coupled modeling can be useful in guiding when to drill infill wells before the altered-stress state negatively affects production outcome.
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Maulianda, Belladonna, Cindy Dhevayani Savitri, Aruvin Prakasan, Eziz Atdayev, Twon Wai Yan, Yew Kwang Yong, Khaled Abdalla Elrais, and Reza Barati. "Recent comprehensive review for extended finite element method (XFEM) based on hydraulic fracturing models for unconventional hydrocarbon reservoirs." Journal of Petroleum Exploration and Production Technology 10, no. 8 (June 8, 2020): 3319–31. http://dx.doi.org/10.1007/s13202-020-00919-z.
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Abstract Hydraulic fracturing has been around for several decades since 1860s. It is one of the methods used to recover unconventional gas reservoirs. Hydraulic fracturing design is a challenging task due to the reservoir heterogeneity, complicated geological setting and in situ stress field. Hence, there are plenty of fracture modelling available to simulate the fracture initiation and propagation. The purpose of this paper is to provide a review on hydraulic fracturing modelling based on current hydraulic fracturing literature. Fundamental theory of hydraulic fracturing modelling is elaborated. Effort is made to cover the analytical and numerical modelling, while focusing on eXtended Finite Element Modelling (XFEM).
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Liangwei, LI. "Coupling numerical model of hydraulic fracturing seepage in soft coal based on elastoplastic damage." E3S Web of Conferences 198 (2020): 01038. http://dx.doi.org/10.1051/e3sconf/202019801038.
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In order to guide the field application of hydraulic fracturing of soft coal in coal mine, based on the elastic-plastic damage theory, the coupling numerical model of soft coal hydraulic fracturing seepage was studied. The porosity strain relationship equation, permeability strain relationship equation, the relationship between permeability and volume plastic tensile strain and volume plastic shear strain of coal and rock mass are derived, and the plastic correction equation and softening parameters are defined. The stress coupling equation and yield criterion are programmed and embedded into the finite difference software FLAC3D for numerical solution. The numerical simulation shows that the numerical calculation model of soft coal hydraulic fracturing conforms to the actual law, and the field fracturing radius investigation experiment is consistent with the numerical simulation results.
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Ren, Lan, Jinzhou Zhao, and Yongquan Hu. "Hydraulic Fracture Extending into Network in Shale: Reviewing Influence Factors and Their Mechanism." Scientific World Journal 2014 (2014): 1–9. http://dx.doi.org/10.1155/2014/847107.
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Hydraulic fracture in shale reservoir presents complex network propagation, which has essential difference with traditional plane biwing fracture at forming mechanism. Based on the research results of experiments, field fracturing practice, theory analysis, and numerical simulation, the influence factors and their mechanism of hydraulic fracture extending into network in shale have been systematically analyzed and discussed. Research results show that the fracture propagation in shale reservoir is influenced by the geological and the engineering factors, which includes rock mineral composition, rock mechanical properties, horizontal stress field, natural fractures, treating net pressure, fracturing fluid viscosity, and fracturing scale. This study has important theoretical value and practical significance to understand fracture network propagation mechanism in shale reservoir and contributes to improving the science and efficiency of shale reservoir fracturing design.
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Hefny, Ashraf, and K. Y. Lo. "The interpretation of horizontal and mixed-mode fractures in hydraulic fracturing tests in rocks." Canadian Geotechnical Journal 29, no. 6 (December 1, 1992): 902–17. http://dx.doi.org/10.1139/t92-102.
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For the design of underground structures in rocks, the states of initial stresses in the rock mass are required. For structures located at great depths, the hydraulic fracturing test for stress measurements is the only practical method. For vertical fractures, existing solutions for calculation of stresses from test results are satisfactory. For horizontal or mixed-mode fractures, appropriate solutions are required. Closed-form solutions for horizontal and mixed-mode fractures including strength anisotrophy are presented. The method enables the determination of which fracture (horizontal or vertical) occurs first at the first breakdown pressure during the test, so appropriate stress calculation may be carried out. Results of hydraulic fracturing tests in three case histories have been reanalyzed using the method developed. It is shown that for horizontal fractures the ranges of stress values computed are considerably reduced compared with existing solutions. The reinterpreted horizontal stresses in a case record are consistent with results of field observations in underground excavations. Experimental requirements for the measurements of rock parameters relevant to the specific stress paths in hydraulic fracturing tests are discussed. Key words : hydraulic fracturing, stress measurements, mixed-mode fractures, underground structures, rock strength.
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Li, Jianxiong, Wen Xiao, Guanzhong Hao, Shiming Dong, Wen Hua, and Xiaolong Li. "Comparison of Different Hydraulic Fracturing Scenarios in Horizontal Wells Using XFEM Based on the Cohesive Zone Method." Energies 12, no. 7 (March 31, 2019): 1232. http://dx.doi.org/10.3390/en12071232.
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Multistage hydraulic fracturing is a highly effective method for creating multiple transverse fractures to improve gas and oil reservoir production. It is critical to minimize the fracture spacing while also ensuring transverse propagation of fractures in multi-fractured horizontal wells. In this paper, a 3D fully coupled pore pressure-stress model based on the extended finite element method (XFEM) combined with the cohesive zone method is established to simulate five different fracturing scenarios in close spacing. The sensitivity of mesh size and the integration method are optimal, which are verified by the highly accurate traditional cohesive zone method. Then, the effect of five different fracturing scenarios on fracture geometries is compared. It is shown that spacing is a key parameter controlling fracture geometries in all fracturing scenarios. Alternative sequential and modified two-step fracturing can significantly reduce the influence of stress shadowing to generate more transverse fractures and form longer effective fractures. The sequential and two-step fracturing see an obvious improvement with increased fracture effective length when the spacing increases. The simultaneous fracturing technique can result in excessive closure of the middle fractures, which causes serious insertion of proppants. These results offer a new insight on optimization of hydraulic fracturing and can be a guidance for typical field cases.
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Shan, Kun, Yanjun Zhang, Yanhao Zheng, Liangzhen Li, and Hao Deng. "Risk Assessment of Fracturing Induced Earthquake in the Qiabuqia Geothermal Field, China." Energies 13, no. 22 (November 16, 2020): 5977. http://dx.doi.org/10.3390/en13225977.
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In order to reduce the harm of induced earthquakes in the process of geothermal energy development, it is necessary to analyze and evaluate the induced earthquake risk of a geothermal site in advance. Based on the tectonic evolution and seismogenic history around the Qiabuqia geothermal field, the focal mechanism of the earthquake was determined, and then the magnitude and direction of in-situ stress were inversed with the survey data. At the depth of more than 5 km, the maximum principal stress is distributed along NE 37°, and the maximum principal stress reaches 82 MPa at the depth of 3500 m. The induced earthquakes are evaluated by using artificial neural network (ANN) combined with in-situ stress, focal mechanism, and tectonic conditions. The predicted earthquake maximum magnitude is close to magnitude 3.
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Li, Lian Chong, Chun An Tang, Leslie George Tham, Tian Hong Yang, and Shao Hong Wang. "Simulation of Multiple Hydraulic Fracturing in Non-Uniform Pore Pressure Field." Advanced Materials Research 9 (September 2005): 163–72. http://dx.doi.org/10.4028/www.scientific.net/amr.9.163.
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A series of numerical simulations of hydraulic fracturing were performed to study the initiation, propagation and breakdown of fluid driven fractures. The simulations are conducted with a flow-coupled Rock Failure Process Analysis code (RFPA2D). Both heterogeneity and permeability of the rocks are taken into account in the studies. The simulated results reflect macroscopic failure evolution process induced by microscopic fracture subjected to porosity pressure, which are well agreeable to the character of multiple hydraulic fracturing experiments. Based on the modeling results, it is pointed out that fracture is influenced not only by pore pressure magnitude on a local scale around the fracture tip but also by the orientation and the distribution of pore pressure gradients on a global scale. The fracture initiation, the orientation of crack path, the breakdown pressure and the stress field evolution around the fracture tip are influenced considerably by the orientation of the pore pressure. The research provides valuable guidance to the designers of hydraulic fracturing engineering.
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Cheng, Yugang, Zhaohui Lu, Xidong Du, Xuefu Zhang, and Mengru Zeng. "A Crack Propagation Control Study of Directional Hydraulic Fracturing Based on Hydraulic Slotting and a Nonuniform Pore Pressure Field." Geofluids 2020 (August 3, 2020): 1–13. http://dx.doi.org/10.1155/2020/8814352.
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Hydraulic fracturing techniques for developing deeply buried coal reservoirs face routine problems related to high initial pressures and limited control over the fracture propagation direction. A novel method of directional hydraulic fracturing (DHF) based on hydraulic slotting in a nonuniform pore pressure field is proposed. A mechanical model is used to address crack initiation and propagation in a nonuniform pore pressure field, where cracks tend to rupture and propagate towards zones of high pore pressure for reducing the effective rock stress more. The crack initiation pressure and propagation morphology are analyzed by rock failure process analysis software. The numerical results show that the directional propagation of hydraulic fracturing cracks is possible when the horizontal stress difference coefficient is less than or equal to 0.5 or the slotting deviation angle is less than or equal to 30°. These findings are in good agreement with experimental results, which support the accuracy and reliability of the proposed method and theory.
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Shi, Shanzhi, Yushi Zou, Lihua Hao, Beibei Chen, Shicheng Zhang, Xinfang Ma, and Shipeng Zhang. "Parameter Sensitivity Analysis of the Hydraulic Fracture Growth Geometry in a Deep Shale Oil Formation: An Experimental Study." Geofluids 2022 (June 26, 2022): 1–12. http://dx.doi.org/10.1155/2022/6878626.
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The depth of shale oil of Fengcheng Formation in Mahu of Junggar Basin, China, is 4500-5000 m. The horizontal principal stress difference of deep shale reservoir is high, which makes it difficult to form complex fractures during fracturing reconstruction. In order to fully understand the law of hydraulic fracture propagation in the formation during fracturing construction, the anisotropy characteristics and basic reservoir physical parameters (mineral composition and rock strength parameters) of rock were obtained through mineral composition test and indoor rock mechanics test (Brazil splitting test), and it was found that the heterogeneity was strong. The true triaxial fracturing simulation experimental system is used to carry out experimental research on full-diameter core rock samples, and the propagation patterns of hydraulic fractures under the influence of different geological factors (in situ stress difference and natural fractures) and engineering factors (pumping rate and fracturing fluid viscosity) are compared and analyzed. The results show that the in situ stress is the most important factor affecting fracture propagation, which determines the direction and shape of fracture propagation. The natural weak surface (lamina/bedding and natural fractures, etc.) in shale reservoir is an important reason for complex fractures. The nature of the weak plane, occurrence, and in situ stress jointly determine whether the fracture can extend through the weak plane. With the increase of pumping rate (18 mL/min to 30 mL/min), the ability of hydraulic fractures to penetrate layers is continuously enhanced. The horizontal principal stress difference of deep shale reservoir is high, and the low viscosity fracturing fluid (10 mPa·s) tends to activate the horizontal bedding, while the high viscosity fracturing fluid (80 mPa·s) tends to directly penetrate the bedding to form the vertical main fracture. Therefore, the fracturing technology of alternating injection of prehigh viscosity fracturing fluid and postlow viscosity fracturing fluid can be adopted to maximize the complexity of fracturing fractures in deep shale reservoirs. The research results are designed to provide theoretical guidance for prediction of hydraulic fracturing fracture propagation in shale reservoir and have certain reference significance for field construction.
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Zhanghua, Lian, Tuo Yuheng, Zhang Qiang, Yu Hao, Mou Yisheng, and Yang Weixing. "Strength analysis of perforated casing in ultra-deep horizontal shale wells during sublevel acidizing and hydraulic fracturing process." Advances in Mechanical Engineering 14, no. 7 (July 2022): 168781322211145. http://dx.doi.org/10.1177/16878132221114592.
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In the process of sublevel acidizing and fracturing, the non-uniform load on production casing is complex, and casing failure occurs frequently, which seriously affects the next step of production, stimulation, and underground safety of the oil and gas well. Aiming at the deformation and failure problem of perforated casing in ultra-deep horizontal wells, residual strength analysis and safety evaluation of directional perforated casing under sublevel acidizing and fracturing conditions were carried out. Due to the large scale difference between the underground formation and casing and the complex geometry of the model, an indirect coupled two-step method was proposed to determine the external load of casing first and then calculate its mechanical strength. By using this method, the stress level and distribution of perforated casing in in-situ stress field of X well are determined, and the safety factor of casing is analyzed. On this basis, considering the redistribution of in-situ stress field in the sublevel acidizing and hydraulic fracturing process, the stress situations on perforated casing under different in-situ stress differences are studied, and the measures to prevent casing failure are given. The proposed calculation method can provide references for casing selection and perforation process design of ultra-deep horizontal wells.
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Xiaojiao, Zhao, Qu Zhan, Xu Xiaofeng, Yu Xiaocong, Fan Heng, and Song Xijin. "Calculation Model of Rock Fracture Pressure with Multifields in the Process of Fracturing." Mathematical Problems in Engineering 2018 (October 17, 2018): 1–9. http://dx.doi.org/10.1155/2018/2098723.
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In this paper, a comprehensive model to calculate the rock fracture pressure by the theory of double effective stress of porous medium is established, which considers such effective factors as the crustal stress field, hydration stress field, temperature field, tectonic stress field, the porosity of rock, and additional stress field generated by seepage of drilling fluid. This new model is applicable to predict the fracture pressure of different types of rocks. Using the experimental parameters of field fracturing and the experimental results of three-axis compression of rock cores with different water contents, we may get the calculated fracture pressure. Compared with the measured fracture pressure in the oilfield, the result calculated in the present study shows good agreement. Besides, the effects of water contents on the tensile strength and fracture pressure are analyzed. Results show that both the tensile strength and fracture pressure decrease with the increase of water contents, which is due to the reduction of the mechanical properties of rocks by hydration.
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Zeng, Yijin, Wan Cheng, Xu Zhang, and Bo Xiao. "A criterion for identifying a mixed-mode I/II hydraulic fracture crossing a natural fracture in the subsurface." Energy Exploration & Exploitation 38, no. 6 (June 9, 2020): 2507–20. http://dx.doi.org/10.1177/0144598720923781.
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Hydraulic fracturing has been proven to be an effective technique for stimulating petroleum reservoirs. During the hydraulic fracturing process, the effects of the natural fracture, perforation orientation, stress reorientation, etc. lead to the production of a non-planar, mixed-mode I/II hydraulic fracture. In this paper, a criterion for a mixed-mode I/II hydraulic fracture crossing a natural fracture was first proposed based on the stress field around the hydraulic and natural fractures. When the compound degree (KII/KI) approaches zero, this criterion can be simplified to identify a pure mode I hydraulic fracture crossing a natural fracture. A series of true triaxial fracturing tests were conducted to investigate the influences of natural fracture occurrence and in situ stress on hydraulic fracture propagation. These experimental results agree with the predictions of the proposed criterion.
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Su, Zhou, Zhao Zhong Yang, Xiao Gang Li, Yu Yao He, Jian Zhang, and Teng Jiao Lei. "Modified Approach for Reorientation Fracturing Propagation Trajectory Prediction." Advanced Materials Research 868 (December 2013): 556–63. http://dx.doi.org/10.4028/www.scientific.net/amr.868.556.
Full textAbstract:
Reorientation fracturing of post-phase development of conventional low productive formations and pro-phase development of unconventional reservoirs such as shale gas plays and coalbed methane formations has been and will always be of considerable significance for oil/gas development. Conventional reorientation trajectory prediction results cannot exactly match the field actual fracture mapping propagation ones. Based on the discrepancy, this research focuses on the dominant factors influencing re-fracture propagation path and re-recognizes the disturbed stress field. Taking advantage of the proposed Principle of Maximum Circumferential Tensile Stress, the fracture propagation path is numerically modeled, which is more in conformity with the fracture mapping compared with the conventional one. Finally, the importance of proper estimation of reorientation fracturing propagation trajectory is analyzed.