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1
Cai, Bo, Yun Hong Ding, Yong Jun Lu, Chun Ming He, and Gui Fu Duan. "Leak-Off Coefficient Analysis in Stimulation Treatment Design." Advanced Materials Research 933 (May 2014): 202–5. http://dx.doi.org/10.4028/www.scientific.net/amr.933.202.
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Hydraulic fracturing was first used in the late 1940s and has become a common technique to enhance the production of low-permeability formations.Hydraulic fracturing treatments were pumped into permeable formations with permeable fluids. This means that as the fracturing fluid was being pumped into the formation, a certain proportion of this fluid will being lost into formation as fluid leak-off. Therefore, leak-off coefficient is the most leading parameters of fracturing fluids. The accurate understanding of leak-off coefficient of fracturing fluid is an important guidance to hydraulic fracturing industry design. In this paper, a new field method of leak-off coefficient real time analysis model was presented based on instantaneous shut-in pressure (ISIP). More than 100 wells were fractured using this method in oil field. The results show that average liquid rates of post-fracturing was 22m3/d which double improvement compared with the past treatment wells. It had an important role for hydraulic fracturing stimulation treatment design in low permeability reservoirs and was proven that the new model for hydraulic fracturing treatment is greatly improved.
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Shelukhin, Vladimir, and Mikhail Epov. "Ionic Fracture Fluid Leak-Off." Fluids 4, no. 1 (February 19, 2019): 32. http://dx.doi.org/10.3390/fluids4010032.
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The study is motivated by monitoring the space orientation of a hydrolic fracture used in oil production. Streaming potential arises due to the leakage of ionic fracking fluid under the rock elastic forces which make the fracture disclosure disappear after pumping stops. The vector of electric field correlates with the fracture space orientation since the fluid leakage is directed normally to the fracture surfaces. We develop a mathematical model for the numerical evaluation of the streaming potential magnitude. To this end, we perform an asymptotic analysis taking advantage of scale separation between the fracture disclosure and its length. The contrast between the virgin rock fluid and the fluid invading from the fracture is proved to be crucial in a build up of a net charge at the invasion front. Calculations reveal that an increase of the viscosity and resistivity contrast parameters results in an increase of the streaming potential magnitude. Such a conclusion agrees with laboratory experiments.
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Zhou, Desheng, and Andrew K. Wojtanowicz. "Analysis of Leak-off Tests in Shallow Marine Sediments." Journal of Energy Resources Technology 124, no. 4 (November 20, 2002): 231–38. http://dx.doi.org/10.1115/1.1506322.
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Typical analysis of the Leak-off testing (LOT) in wells assumes elastic wellbore and involves identification of diversion points from linear trends of the recorded plots. However, LOTs from wells in the shallow marine sediments (SMS) are inherently nonlinear and their analysis becomes a problem. The paper presents mathematical models of the pressure-volume behavior for two different possible failures around the casing shoe, annular crack (cement-rock parting) and formation fracture. The study submits that these two failure modes would control abnormal LOT patterns. A general pressure-volume model of LOT has been developed including volumetric effects of wellbore expansion, mud loss into the rock, and propagation of an annular crack or plastic fracture. A diagnostic method is proposed to identify LOT-control mechanisms (i.e., formation fracture, annular crack, or mud loss) by analyzing the shut-in section of the LOT’s plot.
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GARAGASH, DMITRY I., EMMANUEL DETOURNAY, and JOSE I. ADACHI. "Multiscale tip asymptotics in hydraulic fracture with leak-off." Journal of Fluid Mechanics 669 (February 16, 2011): 260–97. http://dx.doi.org/10.1017/s002211201000501x.
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This paper is concerned with an analysis of the near-tip region of a fluid-driven fracture propagating in a permeable saturated rock. The analysis is carried out by considering the stationary problem of a semi-infinite fracture moving at constant speed V. Two basic dissipative processes are taken into account: fracturing of the rock and viscous flow in the fracture, and two fluid balance mechanisms are considered – leak-off and storage of the fracturing fluid in the fracture. It is shown that the solution is characterized by a multiscale singular behaviour at the tip, and that the nature of the dominant singularity depends both on the relative importance of the dissipative processes and on the scale of reference. This solution provides a framework to understand the interaction of representative physical processes near the fracture tip, as well as to track the changing nature of the dominant tip process(es) with the tip velocity and its impact on the global fracture response. Furthermore, it gives a universal scaling of the near-tip processes on the scale of the entire fracture and sets the foundation for developing efficient numerical algorithms relying on accurate modelling of the tip region.
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Cheng, Weiping, and Yongxin Shen. "Frequency Characteristic Analysis of Acoustic Emission Signals of Pipeline Leakage." Water 14, no. 24 (December 7, 2022): 3992. http://dx.doi.org/10.3390/w14243992.
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The leakage detection of a water distribution system (WDS) needs the support of a large number of field data. This paper collected over 6800 leak detection signals from cast iron pipelines used in a WDS. We found that 3280 signals indicated leakage, and the remaining indicated no leakage. The characteristics of the signals were extracted and analyzed from three perspectives: the central frequency of the power spectrum, the spectral roll-off rate, and the spectral flatness. Significant statistical distributions were found. The central frequencies of the leakage signals followed the normal distribution, and their spectral roll-off rates demonstrated the Burr distribution; the Birnbaum–Saunders distribution could describe the spectral flatness of the signals. Based on these characteristics, the recognition rate of the ML model for leak detection was improved. The Random Forest model was used to classify the leakage detection signals. The recall rate was 100%, and the false positive rate was 8.27%.
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Shen, Yue, and Ling Tan Zhang. "Eddy Current Detecting of Leak Hole in Pipeline by Wavelet Packet Signal Analysis Method." Applied Mechanics and Materials 291-294 (February 2013): 2486–91. http://dx.doi.org/10.4028/www.scientific.net/amm.291-294.2486.
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In the process of detecting leak hole in pipeline by intelligent pig with eddy current measuring method, the cut off effect of eddy current field in the closed cross section of leak hole in steel plate is weak due to geometric deformation of eddy current on the edge of the hole produced by destroyed drilling. As a result, the measured signal is very unobvious. Meanwhile, owing to the rough surface of steel plate, the periodic interference generated by movement of the detecting probe cannot be eliminated or be inhibited easily by conventional signal processing methods for its large amplitude and approximate frequency band with the leak hole signals, the signal to noise ratio (SNR) of measured signal is very low and the accurate identification of leak hole cannot be guaranteed. The wavelet transform, with characteristics of time-frequency localization and multiple scales, is a useful and effective method for identifying singularity of the signals and adapts to detect the transient signal or extract non-stationary information in the signals with strong periodic interference and noise. The reconstructing signal SNR will be increased greatly in eddy current detecting of leak hole in the pipeline with wavelet packet analysis of the signal by constructing the self-defined cost function based on maximum SNR to obtain optimal wavelet packet basis function. This ensures good detection and location of leak hole in the pipeline.
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Řezáč, Tomáš, Martin Stašek, Pavel Zbořil, and Petr Špička. "The role of CRP in the diagnosis of postoperative complications in rectal surgery." Polish Journal of Surgery 93, no. 5 (April 22, 2021): 1–5. http://dx.doi.org/10.5604/01.3001.0014.6591.
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Introduction: Postoperative anastomotic leak after rectal resection is a life-threatening complication. Late diagnosis and a severe symptomatic leak may cause almost 18 % mortality. Early diagnosis is a challenging issue because of nonspecific clinical signs in the early postoperative period. Minimally invasive rectal surgery and the implementation of ERAS protocol require appropriate markers of inflammatory complications and leak with high sensitivity. Postoperative serum C-reactive protein values seem to be the right answer for this question. Aim: The presented study aimed to determine the importance and cut-off level of serum C-reactive protein as a possible predictive factor for early anastomotic leak diagnosis in rectal surgery. Material and methods: The retrospective observational analysis of patients after resection for rectal cancer in a period of one year. The observation included risk factors (age, sex, BMI, bowel preparation and the acuteness of surgery), recording of complications and serum values of CRP. Results: The study included 178 patients. 63 patients (35,4 %) had non-complicated postoperative course. The complications were present in 115 cases (64,6 %), including surgical site infection (16,3 %) and anastomotic leak (7,3 %). The mortality was 2,2 %. CRP serum value reached the sensitivity 94,7 % and specificity 72,5 % at POD 4 with cut off value of 131,8 mg/l and the sensitivity of 84,2 % and specificity 82,4 % with cut off 175,4 mg/l, respectively. Conclusions: Postoperative serum C-reactive protein may be used as a predictor of anastomotic leakage. The examination of CRP on the 4th postoperative day may lead to early and safe discharge from the hospital after rectal resection. The implementation of the cut off values detects more than 90 % of anastomotic leaks or septic complications.
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Mazur, Z., A. Carvajal-Martínez, R. Muñoz-Quezada, and R. García-Illescas. "Failure analysis of a leak-off oil pipe from injection valves of an off-shore operating diesel engine." Engineering Failure Analysis 14, no. 1 (January 2007): 196–208. http://dx.doi.org/10.1016/j.engfailanal.2005.10.019.
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Choi, Jung Chan, Zhongqiang Liu, Suzanne Lacasse, and Elin Skurtveit. "Leak-Off Pressure Using Weakly Correlated Geospatial Information and Machine Learning Algorithms." Geosciences 11, no. 4 (April 19, 2021): 181. http://dx.doi.org/10.3390/geosciences11040181.
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Leak-off pressure (LOP) is a key parameter to determine the allowable weight of drilling mud in a well and the in situ horizontal stress. The LOP test is run in situ and is frequently used by the petroleum industry. If the well pressure exceeds the LOP, wellbore instability may occur, with hydraulic fracturing and large mud losses in the formation. A reliable prediction of LOP is required to ensure safe and economical drilling operations. The prediction of LOP is challenging because it is affected by the usually complex earlier geological loading history, and the values of LOP and their measurements can vary significantly geospatially. This paper investigates the ability of machine learning algorithms to predict leak-off pressure on the basis of geospatial information of LOP measurements. About 3000 LOP test data were collected from 1800 exploration wells offshore Norway. Three machine learning algorithms (the deep neural network (DNN), random forest (RF), and support vector machine (SVM) algorithms) optimized by three hyperparameter search methods (the grid search, randomized search and Bayesian search) were compared with multivariate regression analysis. The Bayesian search algorithm needed fewer iterations than the grid search algorithms to find an optimal combination of hyperparameters. The three machine learning algorithms showed better performance than the multivariate linear regression when the features of the geospatial inputs were properly scaled. The RF algorithm gave the most promising results regardless of data scaling. If the data were not scaled, the DNN and SVM algorithms, even with optimized parameters, did not provide significantly improved test scores compared to the multivariate regression analysis. The analyses also showed that when the number of data points in a geographical setting is much smaller than that of other geographical areas, the prediction accuracy reduces significantly.
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Kim, Youngseok, Haewook Jung, Jaesuk Ryou, and Jaehyuk Choi. "A Basic Experimental Study on Analysis of Leak Signal and Monitoring Method for Water Supply Pipe." Applied Sciences 11, no. 5 (February 26, 2021): 2097. http://dx.doi.org/10.3390/app11052097.
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Water supply systems are essential elements for human life and industry, and water leaks and water supply cut-off may cause major problems. Local water leaks and pipe failures in the water supply system are inevitable problems due to the aging of pipes. Therefore, leakage detection and prevention are required to monitor the integrity of the water supply system. This paper is a fundamental study on the applicability of the smart bolt, which was developed as a monitoring system to detect water leakage in water supply monitoring. Detection experiments were conducted using a smart bolt with a built-in strain sensor and an accelerometer. Through finite element analysis using ANSYS 2019 R2 and tensile strength testing, the strength of the smart bolt was confirmed to have the acceptable tensile strength. The smart bolt used in this study was verified to meet the allowable criteria of torque and tensile stress for a municipal water supply system. The frequency responses of the simulated leakage pipe system, according to the leakage of the valve and the main pipe, were analyzed, and a leak signal at the valve leak point was detected in the 60-Hz band. The main pipe leaking point was observed to produce a leak signal with a much higher-order mode than that of the valve leak point. Therefore, the smart bolt can be applied to detect warning leak signs from water supply valves and to monitor for loosening of the bolts.
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AlKautsar, Teuku, and Arie Saputra. "Analysis of Boiler Start-Up Failure Risk with Grey FMEA and RCA Methods in Pt. PLTU Nagan Raya." Jurnal Inotera 7, no. 2 (September 19, 2022): 109–19. http://dx.doi.org/10.31572/inotera.vol7.iss2.2022.id181.
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PT. PLN (Persero) UPK Nagan Raya is a Steam Power Plant (PLTU) that uses coal as Boiler fuel to produce thermal energy. one of the initial stages of the Boiler is Startup as the basis for the start of Boiler operations. The purpose of this study is to analyze and avoid the risks that can make the operating system not run. Based on the research conducted, there are 8 risks that can cause failure. Based on the Grey FMEA method, the priority risk that occurs is that the FO fast shut-off cannot be O / C CCR with a value of 0.491 and also in the flexible joint line of the lower burner air there is a leak of 0.503. The result of the Root Cause Analysis method, the cause of the FO fast shut-off cannot be O / C CCR is the limited facilities and infrastructure for device maintenance which causes obstacles for workers so that the results worked on are not effective and efficient. Meanwhile, the risk that the flexible joint line air lower burner has a leak because it is not critical equipment only used at certain times so the check is neglected which makes the flexible joint leak. The solution that can be done is that as much as possible the operator must carry out routine maintenance/overhaul on the flexible joint so that there is no failure that can hinder the operation.
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Tassone, David, Simon Holford, Rosalind King, and Guillaume Backé. "New constraints on stress and fracture orientations in the Shipwreck Trough, Otway Basin: implications for conventional and unconventional exploration and production." APPEA Journal 52, no. 2 (2012): 697. http://dx.doi.org/10.1071/aj11111.
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A detailed understanding of the in-situ stress tensor within energy-rich basins is integral for planning successful drilling completions, evaluating the reactivation potential of sealing faults and developing unconventional plays where fracture stimulation strategies are required to enhance low permeability reservoirs. Newly available leak-off test results interpreted using a new method for analysing leak-off test data constrains the minimal horizontal stress magnitude for the offshore Shipwreck Trough wells to be ∼20 MPa/km, which is similar to the vertical stress magnitude derived from wireline data for depths shallower than ∼2–2.5 km. Breakouts interpreted from image log data reveal a ∼northwest–southeast maximum horizontal stress orientation and formation pressure tests confirm near-hydrostatic conditions for all wells. The new method for analysing leak-off test data has constrained the upper limit of the maximum horizontal stress magnitude to be the greatest, indicating a reverse-to-strike-slip faulting regime, which is consistent with neotectonic faulting evidence. Petrophysical wireline data and image log data to characterise extant natural fracture populations within conventional reservoirs and stratigraphic units that may be exploited as future unconventional reservoirs have also been used. These fracture sets are compared with possible fracture populations recognised in contiguous, high-fidelity 3D seismic datasets using a new method for identifying fracture systems based on attribute mapping techniques. This study represents the first of its kind in the Otway Basin. Combined analysis of the in-situ stress tensor and fracture density and geometries provides a powerful workflow for constraining fracture-related fluid flow pathways in sedimentary basins.
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Hill, Joshua S., Erin Marie Hanna, Susie C. Hurley, Mark Reames, and Jonathan C. Salo. "Relationship of drain amylase and anastomotic leak after esophagectomy." Journal of Clinical Oncology 31, no. 4_suppl (February 1, 2013): 118. http://dx.doi.org/10.1200/jco.2013.31.4_suppl.118.
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118 Background: Esophagectomy is considered the only curative approach in patients with esophageal cancers without locally advanced or metastasis. Anastomotic leak can lead to significant morbidity and mortality. CT esophagram (CTE) is a sensitive method of evaluating for leak; however this test carries with it financial cost and radiation exposure. This study evaluates the utility of drain amylase in the prediction of anastomotic leak. Methods: Fifty-nine patients underwent esophagectomy between 3/10 and 8/12; serial drain amylases and CTE were obtained in 50. Leak was defined by extravasation of contrast or the presence of empyema on CTE. Elevated drain amylase was defined as any level > 400 IU/L. Chi-square and descriptive statistics were performed and the sensitivity of drain amylase >400 IU/L in predicting leak was calculated. Results: A minimally invasive esophagectomy was performed in 47, and an open Ivor-Lewis in 2 and a minimally invasive Ivor-Lewis in 1. Stapled intra-thoracic anastomoses were performed in 47, 3 had a cervical anastomoses. Average age was 61 years and 84% were males. Leak occurred in 6 patients (12.5%). One patient with a late leak was excluded from analysis as they did not have concurrent drain amylase values. This patient had low amylase levels and a normal CTE, though later presented with leak. The overall peri-operative mortality rate was 4.2% (2/48). Mortality in the non-leak and leak cohorts were 0% & 33%. Drain amylase was an accurate marker of anastomotic leak. Of 6 patients with an elevated drain amylase, 5 had an anastomotic leak (sensitivity 83.3%). 40/41 patients with low drain amylase had no leak. Using a cut-off value of 400 IU/L, the negative predictive value of drain amylase in predicting leak after esophagectomy was 97.6% (95%CI; 85.6, 99.9). Conclusions: Drain amylase is a simple and inexpensive test that has excellent sensitivity and negative prediction for the detection of anastomotic leak after esophagectomy. To our knowledge, this is the first study to demonstrate this finding. Routine evaluation of drain amylase may safely replace CTE in the management of patients after esophagectomy, thus reducing radiation exposure and overall cost.
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Wojtanowicz, A. K., and D. Zhou. "Borehole Failure Resulting From Formation Integrity (Leak-Off) Testing in Upper Marine Sediments Offshore." Journal of Energy Resources Technology 120, no. 2 (June 1, 1998): 111–17. http://dx.doi.org/10.1115/1.2795020.
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This paper presents the results of a theoretical study, supported with the finite element analysis, into potential loss of external integrity around a casing shoe resulting from leak-off testing (LOT) in upper marine sediments (UMS). Three types of possible failures from LOTs were considered: vertical fracture, horizontal fracture, and a channel outside cemented annulus. It is proved in the paper that vertical fracture is the most unlikely failure of the three. The other two types of failure can be distinguished by different values of propagation pressures. Although horizontal fractures are initiated at low pressure in the plastic zone around the wellbore, they cannot propagate beyond the plastic zone until wellbore pressures exceed overburden pressures. Annular channels, on the other hand, may propagate upwards at pressures lower than overburden pressure. The paper shows that these channels are initiated at pressures equal to the contact stress between cement and rock and their propagation pressures are on average 3.5-fold greater than contact stress. It is also explained how to identify the UMS with high risk of annular channeling during LOTs.
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Liu, Jinjiang, Fuxing Zhang, Peng Qian, and Wenlin Wu. "A new model for predicting fluid loss in fracture-porosity reservoir." Oil & Gas Science and Technology – Revue d’IFP Energies nouvelles 76 (2021): 31. http://dx.doi.org/10.2516/ogst/2021012.
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Drilling fluid loss always occurs in fracture-porosity reservoirs and it causes severe problems. To reduce and prevent lost circulation, it is important to get to know the cause and the characteristic of drilling fluid loss. According to the approach in the reservoir simulation and well test analysis, a new model for drilling fluid loss in fracture-porosity reservoir is presented. Multi fractures in the formation and drilling fluid seepage between fracture and rock matrix have been considered in the model. The governing equations are derived based on the principle of conservation of mass. The model is solved numerically using Newton-Raphson iterative method. The obtained results indicate that drilling fluid leak-off has great influence on the total leakage volume. It is necessary to consider the impact of the drilling fluid leak-off. In addition, influence of formation properties, such as fracture stiffness, rock matrix porosity, rock matrix permeability, and operation factors, such as pressure difference between wellbore and formation, are also analysed in detail in the paper which could help better understand the factors that influence the drilling fluid loss during drilling operation.
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Lee, Yi-Ying, Po-Kuei Hsu, Chien-Sheng Huang, Yu-Chung Wu, and Han-Shui Hsu. "Complications after Chest Tube Removal and Reinterventions in Patients with Digital Drainage Systems." Journal of Clinical Medicine 8, no. 12 (December 1, 2019): 2092. http://dx.doi.org/10.3390/jcm8122092.
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Introduction: Digital thoracic drainage systems are a new technology in minimally invasive thoracic surgery. However, the criteria for chest tube removal in digital thoracic drainage systems have never been evaluated. We aim to investigate the incidence and predictive factors of complications and reinterventions after drainage tube removal in patients with a digital drainage system. Method: Patients who received lung resection surgery and had their chest drainage tubes connected with a digital drainage system were retrospectively reviewed. Results: A total of 497 patients were monitored with digital drainage systems after lung resection surgery. A total of 175 (35.2%) patients had air leak-related complications after drainage tube removals, whereas 25 patients (5.0%) required reintervention. We identified that chest drainage duration of five days was an optimal cut-off value in predicting air leak-related complications and reinterventions. In multiple logistic regression analysis, previous chest surgery history; small size (16 Fr.) drainage tubes; the presence of initial air leaks, defined as air leaks recorded by the digital drainage system immediately after operation; and duration of chest drainage ≥5 days were independent factors of air leak-related complications, whereas the presence of initial air leaks and duration of chest drainage ≥5 days were independent predictive factors of reintervention after drainage tube removal. Conclusion: Air leak-related complications and reinterventions after drainage tube removals happened in 35.2% and 5.0% of patients with digital thoracic drainage systems. The management of chest drainage tubes in patients with predictive factors, i.e., the presence of initial air leaks and duration of chest drainage of more than five days, should be treated with caution.
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Dontsov, E. V. "Propagation regimes of buoyancy-driven hydraulic fractures with solidification." Journal of Fluid Mechanics 797 (May 16, 2016): 1–28. http://dx.doi.org/10.1017/jfm.2016.274.
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This study investigates the propagation of a semi-infinite buoyancy-driven hydraulic fracture in situations when the fluid is able to solidify along the crack walls. Such problems occur when hot magma ascends from a chamber due to buoyancy forces and solidifies by interacting with colder rock. In the model, the solidification rate is calculated assuming a one-dimensional heat transfer problem, in which case it becomes mathematically equivalent to Carter’s leak-off model, which is commonly used to describe the fluid leak-off from a hydraulic fracture into a porous rock formation. In order to construct a mathematical model for a buoyancy-driven hydraulic fracture with solidification, the aforementioned thermal problem is combined with (i) linear plane-strain elasticity to ensure equilibrium of the rock surrounding the fracture, (ii) linear elastic fracture mechanics to determine the fracture propagation, (iii) lubrication theory to capture the viscous fluid flow inside the crack and to account for the effect of buoyancy, and (iv) volume balance of the magma. To address the problem, the governing equations are first rewritten in terms of one integral equation with a non-singular kernel, which significantly simplifies the analysis and the procedure for obtaining a numerical solution. The latter solution is shown to obey a multiscale behaviour near the fracture tip that is fully resolved by the numerical scheme. In order to understand the structure of the solution and to quantify the regimes of propagation (and the associated transitions), a thorough analysis of the problem has been performed. Finally, the developments are applied to investigate the non-steady propagation of a buoyancy-driven fracture that is fed by a constant flux.
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Gonca, Guven, and Bahri Sahin. "Performance Optimization of an Air-Standard Irreversible Dual-Atkinson Cycle Engine Based on the Ecological Coefficient of Performance Criterion." Scientific World Journal 2014 (2014): 1–10. http://dx.doi.org/10.1155/2014/815787.
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This paper presents an ecological performance analysis and optimization for an air-standard irreversible Dual-Atkinson cycle (DAC) based on the ecological coefficient of performance (ECOP) criterion which includes internal irreversibilities, heat leak, and finite-rate of heat transfer. A comprehensive numerical analysis has been realized so as to investigate the global and optimal performances of the cycle. The results obtained based on the ECOP criterion are compared with a different ecological function which is named as the ecologic objective-function and with the maximum power output conditions. The results have been attained introducing the compression ratio, cut-off ratio, pressure ratio, Atkinson cycle ratio, source temperature ratio, and internal irreversibility parameter. The change of cycle performance with respect to these parameters is investigated and graphically presented.
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Erdil, Nevzat, and Baris Akca. "Risk factors of postoperative atrial fibrillation in patients undergoing beating heart coronary artery bypass." Azerbaijan Journal of Cardiovascular Surgery 3, no. 3 (2022): 76. http://dx.doi.org/10.5455/azjcvs.2022.11.018.
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Aim: This study aims to establish new-onset atrial fibrillation (AF) risk factors and postoperative outcomes after off-pump coronary artery bypass graft (CABG) surgery. Material and Methods: Four hundred ninety patients who underwent off-pump CABG were enclosed in study. Patients divided into two groups in line with the development of new-onset AF as AF group (n=62) and non-AF group (n=428). Groups were compared in terms of preoperative clinical features and perioperative data, and multivariate analysis accomplished to identify independent clinical predictors of AF following off-pump CABG. Results: AF was presented in 62 (12.7%) of the patients, and those were significantly older and had significantly higher additive EuroSCORE scores than without AF. Also patients with postoperative AF had significantly prolonged intensive care unit and longer hospital stays at postoperative period. In the multivariant logistic regression analysis performed, advanced age, mean Euroscore, Mild to moderate mitral regurgitation, Prolonged air leak from thorax drain, mean ventilation time, severe pleural effusion, need for inotropic drug support were found to be risk factors for postoperative AF. Conclusion: Our study showed that age, high Euroscore, mild to moderate mitral regurgitation, prolonged ventilation time, severe pleural effusion and low cardiac output were risk factors of postoperative AF in patients underwent off-pump CABG. Also In patients who developed postoperative AF, prolonged intensive care unit and hospital stays were observed. Prospective randomized studies with larger patient series are recommended to support our study.
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Rapp, John P. "Theoretical model for gene-gene, gene-environment, and gene-sex interactions based on congenic-strain analysis of blood pressure in Dahl salt-sensitive rats." Physiological Genomics 45, no. 16 (August 15, 2013): 737–50. http://dx.doi.org/10.1152/physiolgenomics.00046.2013.
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There is a significant literature describing quantitative trait loci (QTL) controlling blood pressure (BP) in the Dahl salt-sensitive (S) rat. In studies to identify the genes underlying BP QTL it has been common practice to place chromosomal segments from low BP strains on the genetic background of the S rat and then reduce the congenic segments by substitution mapping. The present work suggests a model to simulate genetic interactions found using such congenic strains. The QTL are considered to be switches that can be either in series or in parallel represented by the logic operators AND or OR, respectively. The QTL switches can be on/off switches but are also allowed specific leak properties. The QTL switches are represented by a “universal” switch consisting of two molecules binding to form a complex. Genetic inputs enter the model as allelic products of one of the binding molecules and environmental variation (including dietary salt- and sex-related differences) enters as an influence on the concentration of the other binding molecule. The pairwise interactions of QTL are very well simulated and fall into recognizable patterns. There is, however, often more than one assumed model to predict a given pattern so that all patterns do not necessarily have a unique solution. Nevertheless, the models obtained provide a framework for placing the QTL in pathways relative to one another. Moreover, based on their leak properties pairs of QTL could be identified in which one QTL may alter the properties of the other QTL.
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Heils, Lucas, Martina Schneemann, Ralf Gerhard, Jörg-Dieter Schulzke, and Roland Bücker. "CDT of Clostridioides difficile Induces MLC-Dependent Intestinal Barrier Dysfunction in HT-29/B6 Epithelial Cell Monolayers." Toxins 15, no. 1 (January 7, 2023): 54. http://dx.doi.org/10.3390/toxins15010054.
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Background: Clostridioides difficile binary toxin (CDT) defines the hypervirulence of strains in nosocomial antibiotic-induced colitis with the highest mortality. The objective of our study was to investigate the impact of CDT on the intestinal epithelial barrier and to enlighten the underlying molecular mechanisms. Methods: Functional measurements of epithelial barrier function by macromolecular permeability and electrophysiology were performed in human intestinal HT-29/B6 cell monolayers. Molecular analysis of the spatial distribution of tight junction protein and cytoskeleton was performed by super-resolution STED microscopy. Results: Sublethal concentrations of CDT-induced barrier dysfunction with decreased TER and increased permeability for 332 Da fluorescein and 4 kDa FITC-dextran. The molecular correlate to the functional barrier defect by CDT was found to be a tight junction protein subcellular redistribution with tricellulin, occludin, and claudin-4 off the tight junction domain. This redistribution was shown to be MLCK-dependent. Conclusions: CDT compromised epithelial barrier function in a human intestinal colonic cell model, even in sublethal concentrations, pointing to barrier dysfunction in the intestine and leak flux induction as a diarrheal mechanism. However, this cannot be attributed to the appearance of apoptosis and necrosis, but rather to an opening of the paracellular leak pathway as the result of epithelial tight junction alterations.
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Morimoto, Masaki, Kenjiro Taniguchi, Osamu Yamamoto, Takuji Naka, Atsushi Sugitani, and Yoshiyuki Fujiwara. "Preoperative white blood cell count predicts anastomotic leakage in patients with left-sided colorectal cancer." PLOS ONE 16, no. 10 (October 20, 2021): e0258713. http://dx.doi.org/10.1371/journal.pone.0258713.
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To determine whether preoperative white blood cell (WBC) counts reflect risk of anastomotic leak (AL) for patients with colorectal cancer (CRC), we retrospectively examined data from records of 208 consecutive patients who had undergone resections for left-sided CRC, including their clinicopathological parameters and preoperative laboratory data. The diagnostic value of WBC count for AL was evaluated and compared with those of neutrophil-lymphocyte ratio, platelet-lymphocyte ratio, lymphocyte-monocyte ratio and platelet count × C-reactive protein level multiplier (P-CRP) value; optimal cut-off values were derived from receiver operating characteristic curves. AL was observed in 11 of the 208 patients (5.3%). Compared with the no-AL group, the AL group had a significantly higher mean WBC count and smoking rate. In multivariate analysis, WBC count and smoking were independent risk factors for AL. Compared with the other tested inflammatory indicators, the cut-off value for WBC (6,200/μL) had the highest sensitivity (81.8%) and negative predictive value (98.4%), as well as the lowest likelihood ratio (0.289). Preoperative WBC count could therefore be a convenient predictor of AL in patients with left-sided CRC.
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Vadday, Komal. "P02 Use of intrathecal fluorescein to identify cerebrospinal fluid (CSF) rhinorrhea in paediatrics: a case report and literature review." Archives of Disease in Childhood 107, no. 5 (April 20, 2022): e25.3-e25. http://dx.doi.org/10.1136/archdischild-2022-nppg.11.
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Early identification of CSF rhinorrhoea can reduce the risk of meningitis and potentially decrease the length of hospital stay. To determine the exact site of leak, intrathecal fluorescein (IF) is frequently used as a diagnostic tool adjunct to repair surgery in rhinorrhea. Although this is generally considered safe, there is a slight risk of seizures, radicular symptoms such as numbness and transient paraparesis.1Miss. AB, a 20 month old child weighing 11.6kg with history of traumatic subdural collections was admitted with episodes of absence seizures, ataxia and unresponsiveness. Initial investigations involved an electroencephalogram which reported a normal background rhythm. A follow up MRI scan reported no definite site of abnormal CSF leak to confirm the working diagnosis. Hence, IF was proposed as a diagnostic tool to identify the location of a possible leak. The pharmacist conducted a therapeutic review with the aim of appraising existing evidence for the use of IF in paediatrics.A total of 12 articles were identified using Medline and Embase. 5 case series and 1 case report were selected for further review to determine the safety profile, optimal dose and appropriate formulation for the diagnostic procedure. Studies showed at lower concentrations, with doses ranging from 25-100mg the rate of minor complications such as nausea/vomiting, headache and dizziness was negligible.1 2 No complications were accounted in using the lowest dose (<25mg).2 Another study specifically mentioned no adverse reactions observed in children when 0.1ml/kg of 5% fluorescein was administered.3 The case report presented a paediatric patient (16 months) with CSF leak who was administered 0.125ml (6.25mg) of 5% IT to identify the leak.4 The potential dosage for Miss. AB was decided as between 10mg to 25mg balancing the increasing risk of adverse reactions with higher doses and possibility of false-negative result with lower doses.The neurosurgical team used this evidence to present the patient’s case to the chairman’s board for an off-label use approval at the trust. Upon enquiring various manufactures, the 5% unlicensed injection was unavailable to purchase and the 10% injection is unsuitable for intrathecal use. Therefore, the 20% fluorescence sodium injection which is an unlicensed ‘specials’ product usually used in adults was recommended by pharmacy. The smallest measurable dose of 0.1ml (20mg) of 20% fluorescein sodium, diluted in 10ml CSF with 5ml infused via a 0.2micron filter was recommended. The batch number and pyrogen free certificate was obtained from pharmacy procurement and application was submitted.Upon receiving the panel approval, IF was used and a CSF leak was identified. This has aided the surgeons to confirm diagnosis and repair the rhinorrhea. With this successful intervention, the use of IF can be an established option to diagnose CSF rhinorrhea prior to surgery in the trust. These findings will be used in submitting a formulary application and drafting trust guidance for extending the use of IF to paediatrics as a diagnostic tool in neurosurgery.ReferencesJavadi S, Samimi H, Naderi F, et al. The use of low- dose intrathecal fluorescein in endoscopic repair of cerebrospinal fluid rhinorrhea. Archives of Iranian Medicine 2013;16:264-266.Rainer K, Wienke A, Wolfgang D, et al. Use of sodium fluorescein solution for detection of cerebrospinal fluid fistulas: an analysis of 420 administrations and reported complications in Europe and the United States. Laryngoscope 2004;114:266-272.Crosara P, Becker C, Stamm A, et al. Chemical and cytological analysis of cerebral spinal fluid after intrathecal injection of hypodense fluorescein. Brazilian Journal of Otorhinolaryngology 2015;81:549-553Lue A, Manolidis S. Intrathecal fluorescein to localize cerebrospinal fluid leakage in Bilateral Mondini Dysplasia. Otology & Neurotology 2004;25:50-52.
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Ju, Yang, Jialiang Chen, Yongliang Wang, Feng Gao, and Heping Xie. "Numerical Analysis of Hydrofracturing Behaviors and Mechanisms of Heterogeneous Reservoir Glutenite, Using the Continuum‐Based Discrete Element Method While Considering Hydromechanical Coupling and Leak‐Off Effects." Journal of Geophysical Research: Solid Earth 123, no. 5 (May 2018): 3621–44. http://dx.doi.org/10.1029/2017jb015092.
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Gilchrist, Callum J. D., John W. Cosgrove, and Kevin J. Parmassar. "Critically stressed fractures: analysis of the Shaikan Field, Kurdistan Region of Iraq." Journal of the Geological Society 177, no. 6 (July 23, 2020): 1315–28. http://dx.doi.org/10.1144/jgs2019-136.
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The Shaikan Field is a large producing oil field in the Kurdistan region of Iraq. It consists of multiple fractured reservoirs consisting of limestones, calcareous sandstones and mudstones. The surrounding tectonic terrane is situated in the seismically active Zagros–Taurus orogenic zone, where present-day stresses are high. The regional stresses are found to impose conditions that satisfy failure along reservoir-bound fractures, suggesting that a significant proportion of fractures are likely to be critically stressed. The in situ maximum principal stress magnitudes are estimated using three methods, namely, the tensile and compressive strengths of reservoir rock, and leak-off test (LOT) data. Stress-field orientations are determined from wellbore image log data, which are used to interpret wellbore breakouts and the associated induced tensile fractures. Reservoir pressure has declined since production started and poroelastic responses have been assessed and used to estimate the present-day stress-state and the criticality of those fractures that are most likely to fail or slip. Although a conventional approach has been used the present authors argue that a new approach to stress response with changing pore pressure should be taken. Unlike the previous theory of criticality in which a reduction in pore pressure is considered to lead to a stabilization of the fracture network, the present study suggests that a system may remain critically stressed regardless of pressure decline.Thematic collection: This article is part of the The Geology of Fractured Reservoirs collection available at: https://www.lyellcollection.org/cc/the-geology-of-fractured-reservoirs
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Pradana, A., J. Setyowiyoto, B. Prasetyo, and W. Haidar. "Overpressure’s top and generating mechanism in “APR” block, North Sumatra offshore area." IOP Conference Series: Earth and Environmental Science 851, no. 1 (October 1, 2021): 012046. http://dx.doi.org/10.1088/1755-1315/851/1/012046.
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Abstract The offshore North Sumatra Basin is one of the hydrocarbon-prone basins in Indonesia. The Malacca Formation acts as the reservoir in this basin. However, there are some drilling problems caused by abnormal pore pressures. Overpressure analysis is carried out so that drilling activities are avoided from drilling problems such as kicks, blowouts, stuck pipes, loss circulation, and collapse. This study aims to analyze the overpressure in the “APR” block, offshore North Sumatra Basin, which includes determine the depth of the top overpressure and the mechanism of overpressure formation. In the research area, analysis of 3 exploration wells was carried out. Overpressure is analyzed based on well log data, and pressure test data using the Eaton method (1975) supported by other data such as LOT (Leak-Off Test) data, drilling reports, mudlogs. At Well A, top overpressure depth is ± 3235 ft TVDSS (true vertical depth sub sea). At Well P, top overpressure depth is ± 3065 ft TVDSS, and at Well R, top overpressure depth is ± 2901 ft TVDML (true vertical depth mud line). The overpressure generating mechanism in the study area is caused by the loading mechanism (disequilibrium compaction) and caused by the nonloading mechanism (hydrocarbon buoyancy).
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Ciurluini, Cristiano, Fabio Giannetti, Alessandro Del Nevo, and Gianfranco Caruso. "Study of the EU-DEMO WCLL Breeding Blanket Primary Cooling Circuits Thermal-Hydraulic Performances during Transients Belonging to LOFA Category." Energies 14, no. 6 (March 11, 2021): 1541. http://dx.doi.org/10.3390/en14061541.
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The Breeding Blanket (BB) is one of the key components of the European Demonstration (EU-DEMO) fusion reactor. Its main subsystems, the Breeder Zone (BZ) and the First Wall (FW), are cooled by two independent cooling circuits, called Primary Heat Transfer Systems (PHTS). Evaluating the BB PHTS performances in anticipated transient and accident conditions is a relevant issue for the design of these cooling systems. Within the framework of the EUROfusion Work Package Breeding Blanket, it was performed a thermal-hydraulic analysis of the PHTS during transient conditions belonging to the category of “Decrease in Coolant System Flow Rate”, by using Reactor Excursion Leak Analysis Program (RELAP5) Mod3.3. The BB, the PHTS circuits, the BZ Once Through Steam Generators and the FW Heat Exchangers were included in the study. Selected transients consist in partial and complete Loss of Flow Accident (LOFA) involving either the BZ or the FW PHTS Main Coolant Pumps (MCPs). The influence of the loss of off-site power, combined with the accident occurrence, was also investigated. The transient analysis was performed with the aim of design improvement. The current practice of a standard Pressurized Water Reactor (PWR) was adopted to propose and study actuation logics related to each accidental scenario. The appropriateness of the current PHTS design was demonstrated by simulation outcomes.
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SEIM, THORSTEIN, ARNE VALBERG, and BARRY B. LEE. "Visual signal processing in the macaque lateral geniculate nucleus." Visual Neuroscience 29, no. 2 (March 2012): 105–17. http://dx.doi.org/10.1017/s0952523812000065.
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AbstractComparisons of S- or prepotential activity, thought to derive from a retinal ganglion cell afferent, with the activity of relay cells of the lateral geniculate nucleus (LGN) have sometimes implied a loss, or leak, of visual information. The idea of the “leaky” relay cell is reconsidered in the present analysis of prepotential firing and LGN responses of color-opponent cells of the macaque LGN to stimuli varying in size, relative luminance, and spectral distribution. Above a threshold prepotential spike frequency, called the signal transfer threshold (STT), there is a range of more than 2 log units of test field luminance that has a 1:1 relationship between prepotential- and LGN-cell firing rates. Consequently, above this threshold, the LGN cell response can be viewed as an extension of prepotential firing (a “nonleaky relay cell”). The STT level decreased when the size of the stimulus increased beyond the classical receptive field center, indicating that the LGN cell is influenced by factors other than the prepotential input. For opponent ON cells, both the excitatory and the inhibitory response decreased similarly when the test field size increased beyond the center of the receptive field. These findings have consequences for the modeling of LGN cell responses and transmission of visual information, particularly for small fields. For instance, for LGN ON cells, information in the prepotential intensity–response curve for firing rates below the STT is left to be discriminated by OFF cells. Consequently, for a given light adaptation, the STT improves the separation of the response range of retinal ganglion cells into “complementary” ON and OFF pathways.
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Nikitchenko, Maxim, and Alexei Koulakov. "Neural Integrator: A Sandpile Model." Neural Computation 20, no. 10 (October 2008): 2379–417. http://dx.doi.org/10.1162/neco.2008.12-06-416.
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We investigated a model for the neural integrator based on hysteretic units connected by positive feedback. Hysteresis is assumed to emerge from the intrinsic properties of the cells. We consider the recurrent networks containing either bistable or multistable neurons. We apply our analysis to the oculomotor velocity-to-position neural integrator that calculates eye positions using the inputs that carry information about eye angular velocity. By analyzing this system in the parameter space, we show the following. The direction of hysteresis in the neuronal response may be reversed for the system with recurrent connections compared to the case of unconnected neurons. Thus, for the NMDA receptor-based bistability, the firing rates after ON saccades may be higher than after OFF saccades for the same eye position. The reversal of hysteresis occurs in this model only when the size of hysteresis differs from neuron to neuron. We also relate the macroscopic leak time constant of the integrator to the rate of microscopic spontaneous noise-driven transitions in the hysteretic units. Finally, we investigate the conditions under which the hysteretic integrator may have no threshold for integration.
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Shmaya, Tomer, and Avi Ostfeld. "A Graph-Theory-Based PRV Placement Algorithm for Reducing Water Age in Water Distribution Systems." Water 14, no. 23 (November 22, 2022): 3796. http://dx.doi.org/10.3390/w14233796.
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Water age is the time taken for water to travel through a distribution system and reach the consumer. Generally, there is a trade-off between water pressure and water age in a water distribution system—higher pressure results in higher flow velocity, which often means shorter traveling time for the water, while lower pressure leads to slower flow and thus higher water age. Low pressure is a desired objective in a distribution system, as it reduces the physical stress on its components and minimizes water losses in the event of a leak. Low water age is a desired objective as well, as increased age is regarded as having a low water quality. Therefore, the two objectives compete with one another. The problem of trying to minimize both water pressure and age is a common problem in water distribution systems’ design and management. This paper introduces an algorithm for pressure reducing valves’ (PRVs) placement for reducing water age in water distribution systems. The algorithm is based on graph-theory elements and uses EPANET 2.2 for simulation and analysis. The method is demonstrated on two small scale examples, and the results present relatively significant improvements in respect to water age.
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Ju, Yang, Yongliang Wang, Jialiang Chen, Feng Gao, and Jianguo Wang. "Adaptive finite element-discrete element method for numerical analysis of the multistage hydrofracturing of horizontal wells in tight reservoirs considering pre-existing fractures, hydromechanical coupling, and leak-off effects." Journal of Natural Gas Science and Engineering 54 (June 2018): 266–82. http://dx.doi.org/10.1016/j.jngse.2018.04.015.
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Ajayi, Kehinde E., Azubuike H. Amadi, Victor D. Ola, Raphael E. Obonin, and Nnaemeka Achara. "Prediction of Fracture Pressure in Niger Delta Deep Offshore." European Journal of Engineering and Technology Research 6, no. 2 (February 4, 2021): 13–18. http://dx.doi.org/10.24018/ejers.2021.6.2.2353.
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During drilling operations, it is essential to keep the wellbore pressure within the maximum value of the fracture pressure and minimum value of the pore pressure of the formation. To handle this challenge, the fracture pressure of the formation must be known as it is significant to determining the mud window design. This study developed a correlation that could predict the formation fracture pressure in the Niger Delta deep offshore field. Two different fields were considered for this model named Field 1 and 2. From these fields, fracture pressure data were gotten from 21 wells during leak off test (LOT) at different casing shoe depths. While carrying-out the analysis of data, assumptions were made that the formations throughout the Niger Delta basin obeys the principle of horizontality. Also, that the fracture pressure at same depth is uniform with the pressure at other location in the Delta. Scatter plot was used as the tool for the data analysis. A line of best fit was drawn to arrive at the correlation. This correlation has an R2 coefficient values of 0.9969. In conclusion, the correlation gotten from this study for predicting fracture pressure has shown to align with some data sets from the Niger Delta fields with very little variation. This can be used for planning of further drilling operations in the Niger Delta to make it easier, faster and more economical.
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Ajayi, Kehinde E., Azubuike H. Amadi, Victor D. Ola, Raphael E. Obonin, and Nnaemeka Achara. "Prediction of Fracture Pressure in Niger Delta Deep Offshore." European Journal of Engineering and Technology Research 6, no. 2 (February 4, 2021): 13–18. http://dx.doi.org/10.24018/ejeng.2021.6.2.2353.
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During drilling operations, it is essential to keep the wellbore pressure within the maximum value of the fracture pressure and minimum value of the pore pressure of the formation. To handle this challenge, the fracture pressure of the formation must be known as it is significant to determining the mud window design. This study developed a correlation that could predict the formation fracture pressure in the Niger Delta deep offshore field. Two different fields were considered for this model named Field 1 and 2. From these fields, fracture pressure data were gotten from 21 wells during leak off test (LOT) at different casing shoe depths. While carrying-out the analysis of data, assumptions were made that the formations throughout the Niger Delta basin obeys the principle of horizontality. Also, that the fracture pressure at same depth is uniform with the pressure at other location in the Delta. Scatter plot was used as the tool for the data analysis. A line of best fit was drawn to arrive at the correlation. This correlation has an R2 coefficient values of 0.9969. In conclusion, the correlation gotten from this study for predicting fracture pressure has shown to align with some data sets from the Niger Delta fields with very little variation. This can be used for planning of further drilling operations in the Niger Delta to make it easier, faster and more economical.
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Elkordy, Ahmed Roushdy, Jiang Zhang, Yahya H. Ezzeldin, Konstantinos Psounis, and Salman Avestimehr. "How Much Privacy Does Federated Learning with Secure Aggregation Guarantee?" Proceedings on Privacy Enhancing Technologies 2023, no. 1 (January 2023): 510–26. http://dx.doi.org/10.56553/popets-2023-0030.
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Federated learning (FL) has attracted growing interest for enabling privacy-preserving machine learning on data stored at multiple users while avoiding moving the data off-device. However, while data never leaves users’ devices, privacy still cannot be guaranteed since significant computations on users’ training data are shared in the form of trained local models. These local models have recently been shown to pose a substantial privacy threat through different privacy attacks such as model inversion attacks. As a remedy, Secure Aggregation (SA) has been developed as a framework to preserve privacy in FL, by guaranteeing the server can only learn the global aggregated model update but not the individual model updates.While SA ensures no additional information is leaked about the individual model update beyond the aggregated model update, there are no formal guarantees on how much privacy FL with SA can actually offer; as information about the individual dataset can still potentially leak through the aggregated model computed at the server. In this work, we perform a first analysis of the formal privacy guarantees for FL with SA. Specifically, we use Mutual Information (MI) as a quantification metric and derive upper bounds on how much information about each user's dataset can leak through the aggregated model update. When using the FedSGD aggregation algorithm, our theoretical bounds show that the amount of privacy leakage reduces linearly with the number of users participating in FL with SA. To validate our theoretical bounds, we use an MI Neural Estimator to empirically evaluate the privacy leakage under different FL setups on both the MNIST and CIFAR10 datasets. Our experiments verify our theoretical bounds for FedSGD, which show a reduction in privacy leakage as the number of users and local batch size grow, and an increase in privacy leakage as the number of training rounds increases. We also observe similar dependencies for the FedAvg and FedProx protocol.
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Drews, Michael C., Robin Seithel, Alexandros Savvatis, Thomas Kohl, and Harald Stollhofen. "A normal-faulting stress regime in the Bavarian Foreland Molasse Basin? New evidence from detailed analysis of leak-off and formation integrity tests in the greater Munich area, SE-Germany." Tectonophysics 755 (March 2019): 1–9. http://dx.doi.org/10.1016/j.tecto.2019.02.011.
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Funamizu, Naotake, Kenji Omura, Yasutsugu Takada, Takahiro Ozaki, Kohei Mishima, Kazuharu Igarashi, and Go Wakabayashi. "Geriatric Nutritional Risk Index Less Than 92 Is a Predictor for Late Postpancreatectomy Hemorrhage Following Pancreatoduodenectomy: A Retrospective Cohort Study." Cancers 12, no. 10 (September 28, 2020): 2779. http://dx.doi.org/10.3390/cancers12102779.
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Postpancreatectomy hemorrhage (PPH) is the most lethal complication of pancreatoduodenectomy (PD). The main risk factor for PPH is the development of a postoperative pancreatic fistula (POPF). Recent evidence shows that the geriatric nutritional risk index (GNRI) may be predictive indicator for POPF. In this study, we aimed to evaluate whether GNRI is a reliable predictive marker for PPH following PD. The present study retrospectively evaluated 121 patients treated with PD at Ageo Central General Hospital in Japan between January 2015 and March 2020. We investigated the potential of age, gender, body mass index, serum albumin, American Society of Anesthesiologists classification (ASA), diabetes mellitus and smoking status, time taken for the operation, estimated blood loss, and postoperative complications (POPF, bile leak, and surgical site infections) to predict the risk of PPH following PD using univariate and multivariate analyses. Ten patients had developed PPH with an incidence of 8.3%. Among them, the patients were divided into bleeding group (n = 10) and non-bleeding group (n = 111). The bleeding group had significantly lower GNRI values than those in the non-bleeding group (p = 0.001). We determined that the cut-off value of GNRI was 92 accounting for a sensitivity 80.0%, specificity 82.9%, and likelihood ratio of 4.6 using receiver operating characteristic curve analysis. A GNRI of <92 was statistically associated with PPH in both univariate (p < 0.001) and multivariate analysis (p = 0.01). Therefore, we could identify that a GNRI < 92 was an independently potential predictor of PPH risk following PD. We should alert surgeons if patients have low level GNRI before PD.
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Kavurmaci, Önder, Ali Ozdil, Tevfik Ilker Akçam, Ayse Gul Ergonul, Kutsal Turhan, Alpaslan Cakan, and Ufuk Cagirici. "Association of Daily Step Count with the Prolonged Air Leak in Thoracic Surgery Patients." Thoracic and Cardiovascular Surgeon 68, no. 03 (October 31, 2018): 246–52. http://dx.doi.org/10.1055/s-0038-1673661.
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Abstract Background In thoracic surgery clinics, patients are encouraged to walk; however, to our knowledge, there is no data regarding the minimum step count necessary to protect them from complications. In our study, we aim to ascertain the relationship between walking and prolonged air leak (PAL), which is one of the most common complications following thoracic surgery. Methods Patients, who were being followed-up at our clinic between December 2016 and July 2017, were separated into three groups and were investigated prospectively. The groups were established as follows: Group I, included patients with spontaneous pneumothorax; Group II, comprised patients who were applied sublobar lung resection; and Group III, comprised (pneumonectomy excluded) patients who were applied anatomic lung resection. All the patients were supplied with a standard pedometer. The step counts of the patients were recorded prospectively, beginning from the first postoperative day, and an attempt was made to establish the relationship between the patients' daily and mean step counts and the development of PAL. Results PAL developed in 11 (39.29%) of the 28 patients in Group I; in 1 (2.04%) of the 49 patients in Group II and in 22 (36.07%) of the 61 patients in Group III. When receiver operating characteristic (ROC) analysis was applied to the data of Group I, and when the cut-off value for the first-day step count was confirmed to be 2,513 steps, it was revealed that the development of PAL could be determined with a sensitivity of 100% and a specificity of 100%. The analysis of the patients in Group III revealed significant correlations between the first-day and second-day step counts, and the development of PAL (p = 0.017 and 0.007, respectively). The development of PAL decreased as walking was maximized. Conclusion Early and sufficient mobilization decreases the likelihood of postoperative complications. Our study defines concepts, such as post-operative daily step count, target step count, and step count protecting from PAL, and in this regard, we consider it to be a primary study in the literature.
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Trilochana, S., H. M. Somashekarappa, K. Sudeep Kumara, M. P. Mohan, S. Rashmi Nayak, Renita Shiny D’Souza, Srinivas S. Kamath, et al. "A WALK-IN TYPE CALIBRATION CHAMBER FACILITY FOR 222Rn MEASURING DEVICES AND INTER-COMPARISON EXERCISES." Radiation Protection Dosimetry 187, no. 4 (October 29, 2019): 466–81. http://dx.doi.org/10.1093/rpd/ncz188.
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Abstract A walk-in type 222Rn calibration chamber of volume 22.7 m3, which has traceability to international standards, is established at the Centre for Advanced Research in Environmental Radioactivity, Mangalore University, India. It has a human–machine interface communication system, a programmable logic controller and sensor feedback circuit for controlling and data acquisition of relative humidity (RH) and temperature (T). An innovative method for the generation of desired 222Rn concentration (a few hundred Bq m−3 up to about 36 kBq m−3) using soil gas as a source was adopted. Leak rates of 222Rn from the chamber for the mixing fan ON and OFF conditions were determined to be 0.0011 and 0.00018 h−1 respectively. With the exhaust system fully turned on, the maximum clearance rate of the chamber was 0.58 ± 0.07 h−1. Excellent spatial uniformity in 222Rn concentration in the chamber was confirmed (with a mean value of relative standard deviation < 12%) through measurements at 23 locations using CR-39 film-based passive devices. Demonstration of calibration applications was performed using charcoal canister and PicoRad vials as the 222Rn adsorption devices. The study shows that gamma spectrometry is a convenient alternative approach to liquid scintillation analysis of PicoRad vials for 222Rn measurement.
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Liu, Chao, Shuai Guo, Yuan Feng, Feng Hong, Haiguang Huang, and Zhongwen Guo. "L-VTP: Long-Term Vessel Trajectory Prediction Based on Multi-Source Data Analysis." Sensors 19, no. 20 (October 9, 2019): 4365. http://dx.doi.org/10.3390/s19204365.
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With the rapid development of marine IoT (Internet of Things), ocean MDTN (Mobile Delay Tolerant Network) has become a research hot spot. Long-term trajectory prediction is a key issue in MDTN. There are no long-term fine-grained trajectory prediction methods proposed for ocean vessels because a vessel’s mobility pattern lacks map topology support and can be easily influenced by the fish moratorium, sunshine duration, etc. A traditional on-land trajectory prediction algorithm cannot be directly utilized in this field because trajectory characteristics of ocean vessels are far different from that on land. To address the problem above, we propose a novel long-term trajectory prediction algorithm for ocean vessels, called L-VTP, by utilizing multiple sailing related parameters and K-order multivariate Markov Chain. L-VTP utilizes multiple sailing related parameters to build multiple state-transition matrices for trajectory prediction based on quantitative uncertainty analysis of trajectories. Trajectories’ sparsity of ocean vessels results in a critical state missing problem of a high-order state-transition matrix. L-VTP automatically traverses other matrices in a specific sequence in terms of quantitative uncertainty results to overcome this problem. Furthermore, the different mobility models of the same vessel during the day and the night are also exploited to improve the prediction accuracy. Privacy issues have been taken into consideration in this paper. A quantitative model considering Markov order, training metadata and privacy leak degree is proposed to help the participant make the trade-off based on their customized requirements. We have performed extensive experiments on two years of real-world trajectory data that include more than two thousand vessels. The experiment results demonstrate that L-VTP can realize fine-grained long-term trajectory prediction with the consideration of privacy issues. The average error of 4.5-hour fine-grained prediction is less than 500 m. In addition, the proposed method can be extended to 10-hour prediction with an average error of 2.16 km, which is also far less than the communication range of ocean vessel communication devices.
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Gisler, Batoul M. "Uncertainty Quantification for a Hydraulic Fracture Geometry: Application to Woodford Shale Data." Geofluids 2021 (August 21, 2021): 1–14. http://dx.doi.org/10.1155/2021/2138115.
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Hydraulic fracturing enhances hydrocarbon production from low permeability reservoirs. Laboratory tests and direct field measurements do a decent job of predicting the response of the system but are expensive and not easily accessible, thus increasing the need for robust deterministic and numerical solutions. The reliability of these mathematical models hinges on the uncertainties in the input parameters because uncertainty propagates to the output solution resulting in incorrect interpretations. Here, I build a framework for uncertainty quantification for a 1D fracture geometry using Woodford shale data. The proposed framework uses Monte-Carlo-based statistical methods and is comprised of two parts: sensitivity analysis and the probability density functions. Results reveal the transient nature of the sensitivity analysis, showing that Young’s modulus controls the initial pore pressure, which after 1 hour depends on the hydraulic conductivity. Results also show that the leak-off is most sensitive to permeability and thermal expansion coefficient of the rock and that temperature evolution primarily depends on thermal conductivity and the overall heat capacity. Furthermore, the model shows that Young’s modulus controls the initial fracture width, which after 1 hour of injection depends on the thermal expansion coefficient. Finally, the probability density curve of the transient fracture width displays the range of possible fracture aperture and adequate proppant size. The good agreement between the statistical model and field observations shows that the probability density curve can provide a reliable insight into the optimal proppant size.
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Pham, Tung Son, and Lan Cao Mai. "Geomechanical modeling - workflow and Applications." Science and Technology Development Journal 19, no. 1 (March 31, 2016): 5–15. http://dx.doi.org/10.32508/stdj.v19i1.497.
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This work aimed to present a detailed workflow for building a geomechanical model. For a case study, the workflow is then applied to a horizontal well X. The first step in building a geomechanical model is gathering data regarding well information (tubing, casing, deviation…), geological information (type of fault, permeability, reservoir radius, skin…), logs data (density, resistivity, sonic, caliper…), in-situ test data (leak-off test, formation test,…) and core data (tensile strength test, fracture toughness test, tri-axial test…). The second step is to build the geomechanical model using data analysis so that information about state of stress (vertical and principal horizontal stresses, pore pressure, concentration stress around wellbore) and rock mechanical properties (unconfined compressive strength, tensile strength, fracture toughness, Young modulus, Poisson ratio) can be determined. Moreover, the differences in data analysis for vertical and horizontal wells were also mentioned in this work. Furthermore, it is evident that the more data we get, the more accurately a geomechanical model can be built. However, in reality, not all necessary data can be obtained, so this work also explained how to draw the most information from available data so that we can minimize the number of assumptions and uncertainties. An accurate geomechanical model is very essential for others works such as well bore stability or performance prediction of a well stimulation technique. The case study of this work presented the geomechanical modeling for the well X. The paper then presented the application of geomechanical modeling for the Evaluation of High Energy Gas Fracturing performance as well as for Sand Control analysis.
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Spangenberg, Jorge E., Nicolas J. Saintilan, and Sabina Strmić Palinkaš. "Safe, accurate, and precise sulfur isotope analyses of arsenides, sulfarsenides, and arsenic and mercury sulfides by conversion to barium sulfate before EA/IRMS." Analytical and Bioanalytical Chemistry 414, no. 6 (January 23, 2022): 2163–79. http://dx.doi.org/10.1007/s00216-021-03854-y.
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AbstractThe stable isotope ratios of sulfur (δ34S relative to Vienna Cañon Diablo Troilite) in sulfates and sulfides determined by elemental analysis and isotope ratio mass spectrometry (EA/IRMS) have been proven to be a remarkable tool for studies of the (bio)geochemical sulfur cycles in modern and ancient environments. However, the use of EA/IRMS to measure δ34S in arsenides and sulfarsenides may not be straightforward. This difficulty can lead to potential health and environmental hazards in the workplace and analytical problems such as instrument contamination, memory effects, and a non-matrix-matched standardization of δ34S measurements with suitable reference materials. To overcome these practical and analytical challenges, we developed a procedure for sulfur isotope analysis of arsenides, which can also be safely used for EA/IRMS analysis of arsenic sulfides (i.e., realgar, orpiment, arsenopyrite, and arsenian pyrite), and mercury sulfides (cinnabar). The sulfur dioxide produced from off-line EA combustion was trapped in an aqueous barium chloride solution in a leak-free system and precipitated as barium sulfate after quantitative oxidation of hydrogen sulfite by hydrogen peroxide. The derived barium sulfate was analyzed by conventional EA/IRMS, which bracketed the δ34S values of the samples with three international sulfate reference materials. The protocol (BaSO4-EA/IRMS) was validated by analyses of reference materials and laboratory standards of sulfate and sulfides and achieved accuracy and precision comparable with those of direct EA/IRMS. The δ34S values determined by BaSO4-EA/IRMS in sulfides (arsenopyrite, arsenic, and mercury sulfides) samples from different origins were comparable to those obtained by EA/IRMS, and no sulfur isotope fractionations were introduced during sample preparation. We report the first sulfur isotope data of arsenides obtained by BaSO4-EA/IRMS. Graphical abstract
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Ono, Yuko, Takeyasu Kakamu, Hiroaki Kikuchi, Yusuke Mori, Yui Watanabe, and Kazuaki Shinohara. "Expert-Performed Endotracheal Intubation-Related Complications in Trauma Patients: Incidence, Possible Risk Factors, and Outcomes in the Prehospital Setting and Emergency Department." Emergency Medicine International 2018 (June 10, 2018): 1–9. http://dx.doi.org/10.1155/2018/5649476.
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The aim of this study was to determine complication rates and possible risk factors of expert-performed endotracheal intubation (ETI) in patients with trauma, in both the prehospital setting and the emergency department. We also investigated how the occurrence of ETI-related complications affected the survival of trauma patients. This single-center retrospective observational study included all injured patients who underwent anesthesiologist-performed ETI from 2007 to 2017. ETI-related complications were defined as hypoxemia, unrecognized esophageal intubation, regurgitation, cardiac arrest, ETI failure rescued by emergency surgical airway, dental trauma, cuff leak, and mainstem bronchus intubation. Of the 537 patients included, 23.5% experienced at least one complication. Multivariable logistic regression analysis revealed that low Glasgow Coma Scale Score (adjusted odds ratio [AOR], 0.93; 95% confidence interval [CI], 0.88–0.98), elevated heart rate (AOR, 1.01; 95% CI, 1.00–1.02), and three or more ETI attempts (AOR, 15.71; 95% CI, 3.37–73.2) were independent predictors of ETI-related complications. We also found that ETI-related complications decreased the likelihood of survival of trauma patients (AOR, 0.60; 95% CI, 0.38–0.95), independently of age, male sex, Injury Severity Score, Glasgow Coma Scale Score, and off-hours presentation. Our results suggest that airway management in trauma patients carries a very high risk; this finding has implications for the practice of airway management in injured patients.
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Fu, Yige, Drishti Rathod, Ehab Abo-Ali, Vikas Dukhande, and Ketan Patel. "EphA2-Receptor Targeted PEGylated Nanoliposomes for the Treatment of BRAFV600E Mutated Parent- and Vemurafenib-Resistant Melanoma." Pharmaceutics 11, no. 10 (October 1, 2019): 504. http://dx.doi.org/10.3390/pharmaceutics11100504.
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The clinical outcomes of malignant melanoma have improved with the introduction of mitogen-activated protein kinase kinase (MEK) inhibitors. However, off-target toxicities of the MEK inhibitor trametinib (TMB) often result in dose interruption and discontinuation of therapy. The purpose of this study was to anchor a physically stable EphrinA1-mimicking peptide known as YSA (YSAYPDSVPMMS) on TMB-loaded PEGylated nanoliposomes (YTPLs), and evaluate them in BRAFV600E-mutated parent cells (lines A375 and SK-MEL-28) and vemurafenib-resistant cells lines (A375R and SK-MEL-28R) in melanoma. TMB-loaded PEGylated liposomes (TPL) functionalized with nickel-chelated phospholipids were prepared using a modified hydration method. The hydrodynamic diameter and zeta potential values of optimized YTPL were 91.20 ± 12.16 nm and –0.92 ± 3.27 mV, respectively. The drug release study showed TPL did not leak or burst release in 24 h. The hemolysis observed was negligible at therapeutic concentrations of TMB. A differential scanning calorimetry (DSC) study confirmed that TMB was retained in a solubilized state within lipid bilayers. YTPL showed higher intracellular uptake in parental cell lines compared to vemurafenib-resistant cell lines. Western blot analysis and a cytotoxicity study with the EphA2 inhibitor confirmed a reduction in EphA2 expression in resistant cell lines. Thus, EphA2 receptor-targeted nanoliposomes can be useful for metastatic melanoma-specific delivery of TMB.
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Valov, A. V. "On the simultaneous growth of multiple hydraulic fractures emanating from an inclined well." Journal of Physics: Conference Series 2057, no. 1 (October 1, 2021): 012079. http://dx.doi.org/10.1088/1742-6596/2057/1/012079.
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Abstract The primary focus of this paper is to investigate the interaction between simultaneously propagating multiple fractures, initiated from an inclined well. In particular, the aim is to better understand the influence of the well inclination angle on the stress shadow between the fractures and on the overall resulting geometry of individual cracks. To simplify the analysis, the paper assumes the limit of large perforation friction, which leads to a uniform flux distribution between the fractures. The mathematical model for multiple hydraulic fractures is constructed by coupling together the respective models for individual fractures, each representing a single planar fracture model. In this approach, the fracture induced stress or stress shadow from a previous time step is used as an input for a given single hydraulic fracture to propagate independently. Further, to reduce computational burden, the effects associated with tangential stresses and displacements are neglected, whereby the stress interaction between the fractures is solely described by the normal opening and the normal stress component. Numerical results are presented for the storage viscosity dominated regime, whereby the effects of toughness and leak-off are negligible. An interesting behaviour is observed, demonstrating that the well inclination angle plays a significant role on the overall fracture symmetry. For zero inclination, all the fractures are nearly symmetrical and identical. However, once well inclination is introduced, this breaks the symmetry, making a profound effect on the final result.
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Jia, Ru, Caiwei Fan, Bo Liu, Xiaofei Fu, and Yejun Jin. "Analysis of Natural Hydraulic Fracture Risk of Mudstone Cap Rocks in XD Block of Central Depression in Yinggehai Basin, South China Sea." Energies 14, no. 14 (July 6, 2021): 4085. http://dx.doi.org/10.3390/en14144085.
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The Yinggehai Basin is an important Cenozoic gas bearing basin in the South China Sea. With the gradual improvement of gas exploration and over-development in shallow layers, deep overpressured layers have become the main target for natural gas exploration. There are no large-scale faults in the strata above the Meishan Formation in the central depression, and hydraulic fracturing caused by overpressure in mudstone cap rocks is the key factor for the vertical differential distribution of gas. In this paper, based on the leak-off data, pore fluid pressure, and rock mechanics parameters, the Fault Analysis Seal Technology (FAST) method is used to analyze the hydraulic fracture risk of the main mudstones in the central depression. The results show that the blocks in the diapir zone have been subjected to hydraulic fracturing in the Huangliu cap rocks during the whole geological history, and the blocks in the slope zone which is a little distant from the diapirs has a lower overall risk of hydraulic fracture than the diapir zone. In geological history, the cap rocks in slope zone remained closed for a longer time than in diapir zone and being characterized by the hydraulic fracture risk decreases with the distance from the diapirs. These evaluation results are consistent with enrichment of natural gas, which accumulated in both the Yinggehai Formation and Huangliu Formation of the diapir zone, but it only accumulated in the the Huangliu Formations of the slope zone. The most reasonable explanation for the difference of the gas reservoir distribution is that the diapirs promote the development of hydraulic fractures: (1) diapirism transfers deep overpressure to shallow layers; (2) the small fault and fractures induced by diapir activities weakened the cap rock and reduced the critical condition for the natural hydraulic fractures. These effects make the diapir zone more prone to hydraulic fracturing, which are the fundamental reasons for the difference in gas enrichment between the diapir zone and the slope zone.
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Athauda, Avani, Naureen Starling, Ian Chau, David Cunningham, David J. Watkins, Sheela Rao, Eleftheria Kalaitzaki, et al. "Perioperative FLOT plus anti-PD-L1 avelumab (FLOT-A) in resectable oesophagogastric adenocarcinoma (OGA): Interim safety analysis results from the ICONIC trial." Journal of Clinical Oncology 39, no. 3_suppl (January 20, 2021): 201. http://dx.doi.org/10.1200/jco.2021.39.3_suppl.201.
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201 Background: ICONIC is a single-arm phase II trial investigating the safety and efficacy of perioperative FLOT-A in resectable OGA. Following a 3+3 design safety run-in phase, standard dose FLOT with 10mg/kg IV avelumab (dose level 0) q2weeks was taken forward into the main study. The aims of this pre-planned interim analysis were to assess perioperative safety and R0 resection rates. Methods: The interim analysis occurred once the 15th patient treated at dose level 0 reached 30 days post-surgery. Results: At data cut-off, 15 patients had received at least one cycle of FLOT-A and had undergone resection. The median age of patients was 63y (range: 25 – 73). 71% had an ECOG PS of 0. 60% of tumours were staged as T3 at baseline and 40% T2; 67% were N0, 7% N1 and 27% N2. Due to 5-FU related cardiac toxicity, two patients switched to alternative chemotherapy without 5-FU and avelumab. 13/15 patients (87%) completed 4 cycles of pre-operative FLOT-A; of these, five patients had avelumab omitted for one cycle for toxicity evaluation and management. 9/15 patients (60%) experienced a G3/4 adverse event (AE). These were FLOT-A-related in 8/15 patients (53.3%). The commonest G3/4 AEs were febrile neutropenia, neutropenia and diarrhoea. Median time from last chemotherapy to surgery was 6.4 weeks. No delays or failure to proceed to surgery occurred due to avelumab-related complications. 7% of patients had an American Society of Anaesthesiologists (ASA) preoperative risk score of I, 47% a score of II and 47% a score of III. 73% of patients had operations involving a thoracic approach (10 minimally invasive Ivor-Lewis oesophagogastrectomy with two field radical lymphadenectomy, 1 left thoracoabdominal oesophagogastrectomy and 4 gastrectomy with D2 lymphadenectomy). Median time to extubation was 6h (IQR: 4-24). The median Acute Physiology and Chronic Health Evaluation (APACHE) score at day 1 post-op was 12 (IQR: 10-15) with a median of 3 days (IQR: 2-4) of CCU care. No unexpected complications were reported intra-operatively or during post-operative recovery in FLOT-A treated patients. 5/14 evaluable patients at data cut-off (35.7%) had Clavien-Dindo grade II post-operative complications and 3/14 (21.4%) grade IIIa complications; of these 1 patient had an anastomotic leak that was treated endoscopically. There were no emergency re-operations. All 15 patients achieved R0 resections and were discharged home after a median of 13d (IQR: 11-16) in hospital. Conclusions: To date, FLOT-A has not led to unexpected or unusually severe perioperative complications in the context of major complex upper GI surgery for resectable OGA. Clinical trial information: NCT03399071.
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Han, Chao, Zhichuan Guan, Chuanbin Xu, Fuhui Lai, and Pengfei Li. "Study on Method of Determining the Safe Operation Window of Drilling Fluid Density with Credibility in Deep Igneous Rock Strata." Mathematical Problems in Engineering 2021 (April 20, 2021): 1–11. http://dx.doi.org/10.1155/2021/5514427.
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It is difficult to determine the safe operation window of drilling fluid density (SOWDFD) for deep igneous rock strata. Although the formation three-pressure (pore pressure, collapse pressure, and fracture pressure) prediction method with credibility improves the accuracy of formation three-pressure prediction, it still has a large error for deep igneous strata. To solve this problem, a modified method of the SOWDFD in deep igneous rock strata is proposed based on the leakage statistics of adjacent wells. This method is based on the establishment of the SOWDFD with credibility. Through statistical analysis of drilling fluid density of igneous rock leaky formation group in adjacent wells, the fracture leakage law of the formation is revealed and the upper limit of leak-off pressure containing probability information is obtained. Finally, the modified SOWDFD with credibility for deep igneous rock strata is formed. In this work, the proposed method was used to compute the SOWDFD with credibility of SHB well in Xinjiang, China. Results show that the modified density window is consistent with the field drilling conditions and can reflect the narrow density window in the Permian and lower igneous strata. Combined with the formation three-pressure prediction method with credibility and the actual leakage law of adjacent wells, it can effectively improve the prediction accuracy of the SOWDFD for deep igneous rock strata. The findings of the study can help in better understanding of the complex downhole geological environment in deep igneous rock strata and making reasonable drilling design scheme.
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Watson, Alan R., Annette Vigneux, Brian E. Hardy, and J. Williamson Balfe. "Six-Year Experience with CAPD Catheters in Children." Peritoneal Dialysis International: Journal of the International Society for Peritoneal Dialysis 5, no. 2 (April 1985): 119–22. http://dx.doi.org/10.1177/089686088500500208.
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Over a six-year period, 78 chronic peritoneal catheters were implanted in 55 patients; mean age at insertion was 9.6 years (range 0.2 to 19.1 years) and mean body weight was 28.3 kg (range 4.5 to 63 kg). Singlecuff catheters were used almost exclusively and were inserted in the midline under general anesthetic. Complications included leakage (26%) and one-way catheter obstruction (17%). Exit site and/or tunnel infections developed in 25% and hernias in 20% of 55 patients. Twenty-six catheters required replacement or removal. Actuarial catheter survival was 50% at two years. A retrospective analysis of exit-site infections suggested a significant benefit with “covered” as opposed to “uncovered” catheters (p < 0.01). Despite difficulties with catheter function only one patient was taken off CAPD because of a leak into the pleural cavity. Recent experience suggests that paramedian catheter placement and the use of catheters of an appropriate length for children will reduce the incidence of leakage and one-way obstruction. The complications associated with implantation and the long-term use of chronic peritoneal catheters have produced several modifications of the original Tenckhoff catheter (1–4). However, it remains to be established whether single or double cuff catheters result in fewer exit site, tunnel, or peritoneal complications (5). When our program started in 1978, we used double-cuff catheters but subsequently have implanted single-cuff catheters almost exclusively. Our initial experience with exit-site and tunnel infections was encouraging: only one out of 37 catheters had to be replaced because of tunnel infection (6). This paper describes our additional experience and the complications encountered with increasing duration of catheter use in our pediatric population.
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Gischig, Valentin Samuel, Joseph Doetsch, Hansruedi Maurer, Hannes Krietsch, Florian Amann, Keith Frederick Evans, Morteza Nejati, et al. "On the link between stress field and small-scale hydraulic fracture growth in anisotropic rock derived from microseismicity." Solid Earth 9, no. 1 (January 25, 2018): 39–61. http://dx.doi.org/10.5194/se-9-39-2018.
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Abstract. To characterize the stress field at the Grimsel Test Site (GTS) underground rock laboratory, a series of hydrofracturing and overcoring tests were performed. Hydrofracturing was accompanied by seismic monitoring using a network of highly sensitive piezosensors and accelerometers that were able to record small seismic events associated with metre-sized fractures. Due to potential discrepancies between the hydrofracture orientation and stress field estimates from overcoring, it was essential to obtain high-precision hypocentre locations that reliably illuminate fracture growth. Absolute locations were improved using a transverse isotropic P-wave velocity model and by applying joint hypocentre determination that allowed for the computation of station corrections. We further exploited the high degree of waveform similarity of events by applying cluster analysis and relative relocation. Resulting clouds of absolute and relative located seismicity showed a consistent east–west strike and 70° dip for all hydrofractures. The fracture growth direction from microseismicity is consistent with the principal stress orientations from the overcoring stress tests, provided that an anisotropic elastic model for the rock mass is used in the data inversions. The σ1 stress is significantly larger than the other two principal stresses and has a reasonably well-defined orientation that is subparallel to the fracture plane; σ2 and σ3 are almost equal in magnitude and thus lie on a circle defined by the standard errors of the solutions. The poles of the microseismicity planes also lie on this circle towards the north. Analysis of P-wave polarizations suggested double-couple focal mechanisms with both thrust and normal faulting mechanisms present, whereas strike-slip and thrust mechanisms would be expected from the overcoring-derived stress solution. The reasons for these discrepancies can be explained by pressure leak-off, but possibly may also involve stress field rotation around the propagating hydrofracture. Our study demonstrates that microseismicity monitoring along with high-resolution event locations provides valuable information for interpreting stress characterization measurements.