The Experts below are selected from a list of 2664 Experts worldwide ranked by ideXlab platform
Jincai Zhang - One of the best experts on this subject based on the ideXlab platform.
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in situ Stresses controlling hydraulic fracture propagation and fracture breakdown pressure
Journal of Petroleum Science and Engineering, 2018Co-Authors: Yushuai Zhang, Jincai Zhang, Bin Yuan, Shangxian YinAbstract:Abstract In-situ Stress impact on hydraulic fracturing is investigated to enhance hydraulic fracturing performance. Lithology-controlled lower and upper bounds of the Horizontal Stresses are proposed, and an improved Stress polygon method is presented. This improved method can narrow the area of the conventional Stress polygon, particularly in shales; therefore, constrain the in-situ Stress estimate. The lithology-controlled Stresses indicate that a shale has a higher Minimum Horizontal Stress and can be used as a barrier of the hydraulic fracture propagation when hydraulic fracturing is performed in adjacent sandstones. However, when hydraulic fracturing is performed in a shale oil or gas formation, a Stress-barrier formation may not exist on the top or the bottom of the shale reservoir, and this will cause the hydraulic fractures to propagate out of the reservoir zone. We also examine the effects of the maximum and Minimum Horizontal Stresses, shear Stresses and depletion on the fracture initiation, breakdown, propagation and containment. Shear Stresses cause hydraulic fractures kinking; from this evidence, we find that a Horizontal well can be drilled with a certain angle to the Minimum Stress direction because in most cases the hydraulic fractures eventually curve to the maximum Stress direction. In addition, we propose a new method to calculate the fracture breakdown pressure based on fracture mechanics. The proposed method predicts a higher breakdown pressure than the conventional one, which may better estimate the breakdown pressure.
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lithology dependent Minimum Horizontal Stress and in situ Stress estimate
Tectonophysics, 2017Co-Authors: Yushuai Zhang, Jincai ZhangAbstract:Abstract Based on the generalized Hooke's law with coupling Stresses and pore pressure, the Minimum Horizontal Stress is solved with assumption that the vertical, Minimum and maximum Horizontal Stresses are in equilibrium in the subsurface formations. From this derivation, we find that the uniaxial strain method is the Minimum value or lower bound of the Minimum Stress. Using Anderson's faulting theory and this lower bound of the Minimum Horizontal Stress, the coefficient of friction of the fault is derived. It shows that the coefficient of friction may have a much smaller value than what it is commonly assumed (e.g., μ f = 0.6–0.7) for in-situ Stress estimate. Using the derived coefficient of friction, an improved Stress polygon is drawn, which can reduce the uncertainty of in-situ Stress calculation by narrowing the area of the conventional Stress polygon. It also shows that the coefficient of friction of the fault is dependent on lithology. For example, if the formation in the fault is composed of weak shales, then the coefficient of friction of the fault may be small (as low as μ f = 0.2). This implies that this fault is weaker and more likely to have shear failures than the fault composed of sandstones. To avoid the weak fault from shear sliding, it needs to have a higher Minimum Stress and a lower shear Stress. That is, the critically Stressed weak fault maintains a higher Minimum Stress, which explains why a low shear Stress appears in the frictionally weak fault.
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in situ Stress pore pressure and Stress dependent permeability in the southern qinshui basin
International Journal of Rock Mechanics and Mining Sciences, 2011Co-Authors: Jincai Zhang, Zhaoping Meng, Rui WangAbstract:This study focuses on the in-situ Stress, pore pressure and permeability in the Southern Qinshui Basin, one of largest coalbed methane basins in China. Well tests show that permeability in this basin is higher than other coalbed methane reservoirs. This is because it is located in an extensional basin, where the normal faulting Stress regime is dominated. This in-situ Stress regime is advantageous to keep coal cleats open. Hydraulic fracturing tests indicate that the fracture gradient or Minimum Horizontal Stress is much lower than the shales in the Gulf of Mexico and other oil basins. The Minimum Horizontal Stress model is proposed with consideration of the Stress coefficient based on the uniaxial strain method. This model provides a fairly good prediction on the Minimum Stress. Permeability data show that the effective Stress-dependent permeability is pronounced in the coalbed methane reservoir. This is significant for the dual-porosity and dual-permeability coal reservoirs, which consist of coal porous matrices and cleats. The reason is that a rapid increase in effective Stress can induce the closure of cleats, which may cause a permanent loss of permeability in the cleats. This reduces the connectivity between the cleats and coal matrices, hence the coal matrices cannot deliver gas pressure to the cleats for supporting the cleat space. Therefore, slowing down the effective Stress change during production (e.g. slowing reservoir drawdown) can decelerate the permeability reduction. This is particularly important for the reservoir in which the pore pressure is not significantly overpressured, such that in the Southern Qinshui Basin.
Rima Chatterjee - One of the best experts on this subject based on the ideXlab platform.
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mapping of pore pressure in situ Stress and brittleness in unconventional shale reservoir of krishna godavari basin
Journal of Natural Gas Science and Engineering, 2018Co-Authors: Baisakhi Das, Rima ChatterjeeAbstract:Abstract A methodology is demonstrated to estimate brittleness coefficient and in-situ Stress from well log data linking post-stack seismic data in the unconventional Raghavapuram Shale reservoir of Krishna-Godavari basin, India. Post-stack seismic data has been used to estimate pore pressure, in-situ Stress from well logs through multilayered feedforward neural network (MLFN) model. Shear impedance and density sections from post-stack seismic data are generated from conversion of acoustic impedance to shear impedance linking with well log data. Inverted acoustic impedance, shear impedance, density and compressional to shear wave velocity ratio (Vp/Vs) have been used to train the MLFN model for mapping pore pressure and vertical Stress obtained from well logs. Minimum Horizontal Stress is computed for anisotropic shale medium. Differential Stress ratio (DHSR) section is generated from maximum and Minimum Horizontal Stress magnitudes using MLFN models. Brittleness coefficient estimated from static Young's modulus and Poisson's ratio is mapped into post-stack section. Fracture index is computed from dipole shear sonic log data. The brittleness coefficient of 20–45% and DHSR of 7–16% with 20–46% fracture index are noticed in the Raghavapuram Shale. This zones exhibit relatively high values of brittleness coefficient and relatively high DHSR. Fractures will be aligned in high DHSR zones and oriented to the direction of maximum Horizontal Stress. This information may be useful for fracture type prediction and designing hydraulic fracture stimulation.
Sidali Ouadfeul - One of the best experts on this subject based on the ideXlab platform.
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sweet spots discrimination in shale gas reservoirs using seismic and well logs data a case study from the worth basin in the barnett shale
Energy Procedia, 2014Co-Authors: Leila Aliouane, Sidali OuadfeulAbstract:Abstract Here, we present a case study of sweet spots discrimination of the Barnett shale gas reservoir located in the Ft Worth basin (USA) using seismic and well-logs data. Chaos and the ANT-Tracking seismic attributes such are used for natural fractures system identification from seismic data, the map of the Poisson's ratio obtained from the upscaling of well-logs data of a Horizontal well is able to provide an information about the drilling direction which is usually in the Minimum Horizontal Stress profile, the map of the Poisson ratio can provide an information about hardness of the source rock. The set of well logs data is used for geomechanical and petrophysical discrimination of the sweet spots, after discrimination the identified zones are useful for reserves estimation from unconventional shale gas reservoir.
Shengjun Miao - One of the best experts on this subject based on the ideXlab platform.
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present day Stress state and fault stability analysis in the capital area of china constrained by in situ Stress measurements and focal mechanism solutions
Journal of Asian Earth Sciences, 2019Co-Authors: Peng Li, Shengjun MiaoAbstract:Abstract This work proposes to determine the present-day in situ Stress state across both known and suspected faults in the capital area of China and to assess fault stability and consequent seismic hazards. The population of main active faults in the capital area is summarized, and 168 sets of hydraulic fracturing and overcoring data and 84 sets of earthquake focal mechanism solutions are gathered and studied. The available data indicate that reverse and strike-slip faulting Stress regimes are favored at reservoir depths in this region. The ratio of maximum Horizontal Stress to vertical Stress (KH) and the ratio of Minimum Horizontal Stress to vertical Stress (Kh) at a depth of 500 m show complex spatial variations in Stress magnitudes. Generally, KH appears to increase southward, which might suggest that Stress is accumulating in the southern part of the region. The relative Stress magnitude R appears independent of the depth and mainly varies between 0.5 and 1.0. The observation of Stress data suggests a relatively uniform direction (nearly E-W) for the maximum Horizontal principal Stress. The influence of hydrostatic pore pressure on critical Stresses is discussed, and the presence of hydrostatic pore pressure makes faults more conducive to reactivation. Most locations in this region are critically Stressed based on the Coulomb frictional failure criterion and Byerlee’s law with hydrostatic pore pressure; thus, the present-day Stress state appears to be high enough to initiate slip. In addition, the relationship between the tectonic Stress field and earthquakes is discussed.
Mark P Fischer - One of the best experts on this subject based on the ideXlab platform.
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influence of poroelastic behavior on the magnitude of Minimum Horizontal Stress sh in overpressured parts of sedimentary basins
Geology, 1994Co-Authors: Terry Engelder, Mark P FischerAbstract:In many sedimentary basins of the world the Minimum hori- zontal Stress, S h , is greater in overpressured zones than in normally pressured zones at equivalent depths. A common explanation is that the frictional slip on listric normal faults keeps the difference between vertical Stress, S v and S h within certain bounds, and the difference is smaller under lower effective Stress (i.e., higher pore pressure, P p ). However, in the overpressured parts of the central North Sea graben, United Kingdom, and the Sable subbasin of the Scotian Shelf, Canada, conventional friction envelopes underestimate the magnitude of S h . These data instead indicate that S h increases at a rate proportional to but less than the rate of increase of P p , a condition consistent with a P p -induced deformation of the rock called poroelastic behavior. This paper argues that, whereas friction may govern S h in normally pressured basins, poroelastic behavior is responsible for the unusually high S h in the overpres- sured parts of these same basins. Data on the P p and S h gradients from these basins suggest that Δ S h /Δ P p ∼ 0.7.