scholarly journals Mechanistic Analysis of Shale Permeability Evolution Data

2019 ◽  
Author(s):  
Rui Shi ◽  
Jishan Liu ◽  
Derek Elsworth
Keyword(s):  
Permeability Evolution ◽  
Mechanistic Analysis ◽  
Shale Permeability

scholarly journals Permeability of the Hydrated Shale under Cyclic Loading and Unloading Conditions

Geofluids ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-16
Author(s):  
Liu Xianshan ◽  
Li Man ◽  
Xu Ming ◽  
Kang Zhiyong
Keyword(s):  
Cyclic Loading ◽  
Confining Pressure ◽  
Loading Conditions ◽  
Permeability Evolution ◽  
Loading Process ◽  
Cyclic Loading And Unloading ◽  
Initial Loading ◽  
Cyclic Processes ◽  
Loading And Unloading ◽  
Shale Permeability

The hydrated shales under cyclic loading and unloading conditions are common for the shale reservoir development; corresponding mechanical properties and permeability evolution are very significant and should be deeply researched. Firstly, the experiments of the hydrated shales under the above conditions are discussed, showing that the peak strength is lower and corresponding permeability is higher for more days of hydrating treatment. Secondly, the damage theory is proposed to analyze the shale permeability evolution due to hydromechanical damage and get permeability variation under initial loading and unloading conditions, observing that the permeability in the loading process decreases with increasing confining pressure and increases in the unloading process with decreasing confining pressure; however, the former changes much greater than the latter considering the same confining pressure, indicating that the irreversible damage for the hydrated shales in this cyclic condition has resulted in obvious difference of the permeability. Furthermore, the curves between the permeability and confining pressure based on the experimental data are fitted as negative exponential functions under initial loading conditions and power functions under more cyclic loading conditions, showing that more loading process will change the permeability evolution model. However, the permeability while unloading changes smoothly and can be fitted as a power function with the confining pressure. And in addition, the loss ratio and recovery ratio of the permeability have been deeply researched under five cyclic loading and unloading conditions, thoroughly explaining the permeability decreasing variation with more cyclic processes. Finally, the sensitive coefficients of the permeability have been investigated to observe the largest coefficients under initial cyclic conditions and less and less with more cyclic processes, especially the coefficients while loading which are more sensitive to lower confining pressure and smaller while unloading, which is in accordance with the shale permeability loss and recovery variation, revealing the permeability evolution of the hydrated shale under complex extracted environment.

Effects of Heterogeneous Local Swelling and Multiple Pore Types on Coal and Shale Permeability Evolution

2020 ◽  
Author(s):  
Jie Zeng ◽  
Jishan Liu ◽  
Wai Li ◽  
Jianwei Tian ◽  
Yee-Kwong Leong ◽  
...  
Keyword(s):  
Permeability Evolution ◽  
Pore Types ◽  
Shale Permeability

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 Evolution of the Oil Shale Permeability under Real-Time High-Temperature Triaxial Stress in the Jimusar Area, Xinjiang

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-10
Author(s):  
Lusheng Yang ◽  
Peng Li
Keyword(s):  
High Temperature ◽  
Real Time ◽  
Pore Pressure ◽  
Oil Shale ◽  
Growth Stage ◽  
Test System ◽  
Threshold Temperature ◽  
Permeability Evolution ◽  
Volumetric Stress ◽  
Shale Permeability

This paper adopts a real-time high-temperature triaxial seepage test system to study the permeability evolution of oil shale in the Jimusar area, Xinjiang, with the temperature, pore pressure, and volumetric stress. The results indicate that (1) the variation process of the oil shale permeability with the temperature can be divided into three stages: slow growth stage from 20 to 350°C, rapid growth stage from 350 to 500°C with a threshold temperature of 400°C, and growth deceleration stage from 500 to 600°C. (2) With increasing pore pressure, the permeability gradually decreases. Under a volumetric stress of 17 MPa, the permeability decreases the most rapidly from 1 to 2 MPa, and under a volumetric stress of 34 MPa, the permeability decreases the fastest from 1 to 3 MPa. (3) The oil shale permeability decreases with increasing volumetric stress. At room temperature, the decrease magnitude of the permeability is small and increases with increasing temperature. The results can provide a theoretical reference for the analysis of the seepage process of thermal fluids and pyrolysis oil and gas in oil shale.

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.

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.

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