Permeability and Effective Stress in Dipping Gas Shale Formation With Bedding—Experimental Study

2020 ◽  
Vol 142 (10) ◽  
Author(s):  
Yufei Chen ◽  
Changbao Jiang ◽  
Guangzhi Yin ◽  
Andrew K. Wojtanowicz ◽  
Dongming Zhang
Keyword(s):  
Normal Stress ◽  
Effective Stress ◽  
Bedding Plane ◽  
Permeability Change ◽  
Permeability Evolution ◽  
Tangential Stresses ◽  
Significance Levels ◽  
Percent Contribution ◽  
Shale Formation ◽  
Shale Permeability

Abstract Shale gas well deliverability and economics depend on extremely low permeability that is not only dependent on the rock bedding trend but also controlled by in situ stresses. The purpose of this study was to determine relative contributions of normal and tangential stresses with respect to the rock bedding plane on permeability evolution of shale. The study involved an analysis of the rock bedding structure, followed by triaxial testing of rock samples and theoretical modeling. Also simulated were the effects of stress-bedding and load cycling. The results showed shale permeability reduction during the stress loading process and its gradual recovery during the unloading process. Permeability change was more pronounced in response to normal stress but some effects of the tangential stresses were also observed. Moreover, a theoretical model was derived to describe permeability change with effective stress in the presence of normal and tangential stresses. The model was empirically matched with the experimental results. The assessment of relative contributions of normal and tangential stresses was quantified with the analysis of variance (ANOVA). The analysis revealed significance levels of normal stress, and two tangential stresses σt1 and σt2 on shale permeability as 81%, 5%, and 14%, respectively. An almost 20-percent contribution of tangential stress loading to permeability response indicates a need for the improvement in computing effective stress. Therefore, a new method was suggested to determine effective stress when predicting permeability evolution of shale.

Triaxial Testing of Gas Shale Permeability Dependence on Heterogeneous Stress With Respect to Bedding

2019 ◽  
Author(s):  
Yufei Chen ◽  
Changbao Jiang ◽  
Guangzhi Yin ◽  
Andrew K. Wojtanowicz ◽  
Dongming Zhang
Keyword(s):  
Normal Stress ◽  
Tangential Stress ◽  
Shale Gas ◽  
Gas Flow ◽  
Triaxial Testing ◽  
Permeability Change ◽  
Tangential Stresses ◽  
Longmaxi Shale ◽  
Shale Permeability

Abstract Shale gas has recently become the most promising source of unconventional hydrocarbon energy. Shale gas well deliverability and economics depend on extremely low permeability that is not only dependent on the rock bedding trend but is also controlled by in-situ stresses. Thus, prediction of well’s deliverability requires understanding permeability of a dipping shale with natural bedding under conditions of unequal stresses in-situ. The purpose of this study was to determine relative contributions of normal and tangential stresses with respect to the rock bedding plane on permeability evolution of Longmaxi shale in the Sichuan Basin, southwest China. The study involved an analysis of the rock bedding structure, followed with triaxial testing of rock samples and theoretical modeling. We used SEM observation to identify existence of microfractures and numerous inter-particle pores along the shale bedding planes that provide dominant pathways for gas flow depending upon closing stress value. Stress-dependent permeability was tested with a newly-developed multi-functional true triaxial geophysical (TTG) apparatus providing for a steady state gas flow through the rock sample under conditions of normal stress and two unequal tangential stresses. Also simulated were the effects of stress-bedding and load cycling. The results showed shale permeability reduction during the stress loading process and its gradual recovery during the unloading process for both normal and tangential stress loading cycles. A hysteresis of the permeability response to cyclic loading was the largest when normal stress cycling was dominant. Moreover, permeability change was more pronounced in response to normal stress but some effects of the tangential stresses were also observed — particularly when the tangential stresses were dominant. A theoretical model was derived to describe permeability change with effective stress in the presence of normal and tangential stresses. The model was empirically matched with the experimental results. Assessment of relative contributions of normal and tangential stresses was quantified with the analysis of variance (ANOVA). The analysis revealed significance levels of normal stress, and two tangential stresses σt1 and σt2 on shale permeability as 81%, 5% and 14%, respectively, showing dominant effect of normal stress with clear contribution of tangential stresses. An almost 20-percent contribution of tangential stress loading to permeability response indicates a need for improvement in computing effective stress in permeability predictions of the Longmaxi shale. It also warrants testing other gas shales to specifically determine the effect.

scholarly journals COAL PERMEABILITY CHANGE CAUSED BY MINING-INDUCED STRESS

Mining Scince ◽  
2019 ◽  
Vol 26 ◽  
Author(s):  
Lulu Zhang ◽  
Bo Li ◽  
Jianping Wei ◽  
Zhihui Wen ◽  
Yongjie Ren
Keyword(s):  
Experimental Data ◽  
Effective Stress ◽  
Axial Stress ◽  
Sensitivity Index ◽  
Permeability Change ◽  
Permeability Evolution ◽  
Confining Stress ◽  
Coal Permeability ◽  
Calculation Results ◽  
Loading And Unloading

To study coal permeability evolution under the influence of mining actions, we conducted a sensitivity index test on permeability to determine the influence of axial and confining stresses on coal permeability. Loading and unloading tests were performed afterward, and the differences between loading and unloading paths in terms of strain and permeability were studied. A permeability evolution model was built in consideration of absorption swelling and effective stress during modeling. An effective stress calculation model was also built using axial and confining stresses. The calculation results of the two models were compared with experimental data. Results showed that permeability were more sensitive to confining stress than axial stress, and effective stress placed a large weight on confining stress. Large axial and radial deformations at peak strength were observed during unloading. In the unloading phase, the permeability of coal began to increase, and the increment was enhanced by large initial axial stress when confining stress was loaded. permeability sensitivity to axial and confining stresses were used to explain these permeability changes. The calculation results of the models fitted the experimental data well. Therefore, the proposed models can be used to calculate effective stress on the basis of axial and confining stresses and describe permeability change in coal under the influence of mining actions.

scholarly journals Investigation of Shale Permeability Evolution considering Bivalued Effective Stress Coefficients for CO2 Injection

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-11
Author(s):  
Yi Wang ◽  
Hao Wang ◽  
Shangyi Qi ◽  
Shimin Liu ◽  
Yixin Zhao ◽  
...  
Keyword(s):  
Effective Stress ◽  
Gas Flow ◽  
Co2 Injection ◽  
Late Time ◽  
Permeability Evolution ◽  
Experimental Conditions ◽  
Flow Process ◽  
Knudsen Flow ◽  
Study Laboratory ◽  
Shale Permeability

Because of the existence of multiscale pores from nano- to macroscale, a multimechanistic shale gas flow process involving the Darcy and Knudsen flows occurs during gas shale well depletion. The respective contribution of the Darcy and Knudsen flows to the permeability is constantly changing with pressure evolution. In this study, laboratory measurements of shale permeability with CO2 injections were carried out under hydrostatic conditions, using the transient pulse-decay method. The “U”-shape permeability curve resulted in both positive and negative effective stress coefficients (Biot’s coefficient) χ . A permeability turning point was thus created to partition permeability curves into the Darcy and Knudsen sections. The Knudsen effect was proven to be significant at low pressure/late time in the laboratory. Effective stress and sorption-induced deformation have been found to govern the Darcy permeability evolution under the tested experimental conditions. Thus, negative effective stress coefficients, together with the positive ones, should be applied to a nonmonotonic pressure-permeability evolution to explain the concurrent effect of the Darcy flow and Knudsen flow at different pore pressures.

scholarly journals Triaxial testing on water permeability evolution of fractured shale

2021 ◽  
Vol 8 (12) ◽  
Author(s):  
Menglai Wang ◽  
Dongming Zhang
Keyword(s):  
Effective Stress ◽  
Water Permeability ◽  
Ct Scanning ◽  
Permeability Evolution ◽  
Permeability Model ◽  
Reservoir Stimulation ◽  
Bingham Flow ◽  
Wide Range ◽  
Dominant Characteristic ◽  
Shale Permeability

A sound understanding of the water permeability evolution in fractured shale is essential to the optimal hydraulic fracturing (reservoir stimulation) strategies. We have measured the water permeability of six fractured shale samples from Qiongzhusi Formation in southwest China at various pressure and stress conditions. Results showed that the average uniaxial compressive strength (UCS) and average tensile strength of the Qiongzhusi shale samples were 106.3 and 10.131 MPa, respectively. The nanometre-sized (tiny) pore structure is the dominant characteristic of the Qiongzhusi shale. Following this, we proposed a pre-stressing strategy for creating fractures in shale for permeability measurement and its validity was evaluated by CT scanning. Shale water permeability increased with pressure differential. While shale water permeability declined with increasing effective stress, such effect dropped significantly as the effective stress continues to increase. Interestingly, shale permeability increased with pressure when the pressure is relatively low (less than 4 MPa), which is inconsistent with the classic Darcy's theory. This is caused by the Bingham flow that often occurs in tiny pores. Most importantly, the proposed permeability model would fully capture the experimental data with reasonable accuracy in a wide range of stresses.

Stress distributions and paths in clays during pressuremeter tests

2001 ◽  
Vol 38 (3) ◽  
pp. 542-552 ◽  
Author(s):  
V Silvestri ◽  
R Diab
Keyword(s):  
Shear Stress ◽  
Normal Stress ◽  
Prior Knowledge ◽  
Effective Stress ◽  
Stress Distributions ◽  
Stress Strain ◽  
Tangential Stresses ◽  
Constitutive Properties ◽  
Different Levels

This paper presents a novel analysis for the interpretation of pressuremeter tests in clay. No prior knowledge of the constitutive properties of the material is required. Shear, radial, and tangential stresses are determined at various distances from the probe and for different levels of cavity strain. Total and effective stress paths followed by material elements within the deformed soil are represented on shear stress – normal stress diagrams. The analysis is applied to the interpretation of pressuremeter tests carried out in both the field and the laboratory.Key words: pressuremeter tests, clays, novel analysis, stress–strain curves, stress distributions, stress paths.

scholarly journals Evolution of Coal Permeability during Gas Injection—From Initial to Ultimate Equilibrium

Energies ◽  
2018 ◽  
Vol 11 (10) ◽  
pp. 2800 ◽  
Author(s):  
Xingxing Liu ◽  
Jinchang Sheng ◽  
Jishan Liu ◽  
Yunjin Hu
Keyword(s):  
Effective Stress ◽  
Local Equilibrium ◽  
Fracture Aperture ◽  
Permeability Evolution ◽  
Full Spectrum ◽  
Coal Permeability ◽  
Fracture Pressure ◽  
Permeability Changes ◽  
Apparent Equilibrium ◽  
Non Equilibrium

The evolution of coal permeability is vitally important for the effective extraction of coal seam gas. A broad variety of permeability models have been developed under the assumption of local equilibrium, i.e., that the fracture pressure is in equilibrium with the matrix pressure. These models have so far failed to explain observations of coal permeability evolution that are available. This study explores the evolution of coal permeability as a non-equilibrium process. A displacement-based model is developed to define the evolution of permeability as a function of fracture aperture. Permeability evolution is tracked for the full spectrum of response from an initial apparent-equilibrium to an ultimate and final equilibrium. This approach is applied to explain why coal permeability changes even under a constant global effective stress, as reported in the literature. Model results clearly demonstrate that coal permeability changes even if conditions of constant effective stress are maintained for the fracture system during the non-equilibrium period, and that the duration of the transient period, from initial apparent-equilibrium to final equilibrium is primarily determined by both the fracture pressure and gas transport in the coal matrix. Based on these findings, it is concluded that the current assumption of local equilibrium in measurements of coal permeability may not be valid.

Pressure Corrections for the Potential Flow Analysis of Kelvin-Helmholtz Instability

2011 ◽  
Vol 110-116 ◽  
pp. 4628-4635 ◽  
Author(s):  
Mukesh Kumar Awasthi ◽  
Rishi Asthana ◽  
G.S. Agrawal
Keyword(s):  
Normal Stress ◽  
Potential Flow ◽  
Energy Equation ◽  
Mechanical Energy ◽  
Flow Analysis ◽  
Helmholtz Instability ◽  
Viscous Potential Flow ◽  
Two Fluids ◽  
Tangential Stresses ◽  
Viscous Pressure

The present paper deals with the study of viscous contribution to the pressure for the viscous potential flow analysis of Kelvin-Helmholtz instability of two viscous fluids. Viscosity enters through normal stress balance in the viscous potential flow theory and tangential stresses for two fluids are not continuous at the interface. Here we have considered viscous pressure in the normal stress balance along with the irrotational pressure and it is assumed that the addition of this viscous pressure will resolve the discontinuity between the tangential stresses and the tangential velocities at the interface. The viscous pressure is derived by mechanical energy equation and this pressure correction applied to compute the growth rate of Kelvin-Helmholtz instability. A dispersion relation is obtained and a stability criterion is given in the terms of critical value of relative velocity. It has been observed that the inclusion of irrotational shearing stresses stabilizes the system.

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