Investigating the effects of stress creep and effective stress coefficient on stress-dependent permeability measurements of shale rock

An, Cheng; Killough, John; Xia, Xiaoyang

doi:10.1016/j.petrol.2020.108155

Cited by 15 publications

(5 citation statements)

References 16 publications

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“…Hence, a sound understanding of the shale permeability evolution with respect to stress is beneficial to the optimization and strategy-making of commercial shale gas production. The most effective method for investigating the stress dependence of permeability, to date, is to correlate the permeability with effective stress; since it generally shows the compression degree of rock, influencing the pathways (micro-fractures or pores) for fluid flow that controls the permeability evolution [ 39 , 40 ]. In line with the Terzaghi's effective stress theory, we define the effective stress (also called the mean effective stress in other publications) in this study, considering the triaxial stress states, as

where σ e is the effective stress, σ 1 is the axial stress, σ 3 is the confining pressure, α is the Biot's coefficient (in the present study, α = 1), and P p is the pore pressure.…”

Section: Discussionmentioning

confidence: 99%

Section: Stress Dependence Of Permeability and Permeability Modellingmentioning

confidence: 99%

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Triaxial testing on water permeability evolution of fractured shale

Wang¹,

Zhang

2021

R. Soc. open sci.

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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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where σ e is the effective stress, σ 1 is the axial stress, σ 3 is the confining pressure, α is the Biot's coefficient (in the present study, α = 1), and P p is the pore pressure.…”

Section: Discussionmentioning

confidence: 99%

Section: Stress Dependence Of Permeability and Permeability Modellingmentioning

confidence: 99%

Triaxial testing on water permeability evolution of fractured shale

Wang¹,

Zhang

2021

R. Soc. open sci.

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“…Refracturing is a key measure to prevent the production from decline. Incorporating the stress creep mechanism helps provide more accurate permeability results for the field development [13]. In order to describe the change of reservoir permeability with time, this study introduces a normal creep of a natural fracture closure to investigate the relationship between the permeability decline and the optimal refracturing time.…”

Section: Introductionmentioning

confidence: 99%

A Combination Approach of the Numerical Simulation and Data-Driven Analysis for the Impacts of Refracturing Layout and Time on Shale Gas Production

Zhu

Wang

et al. 2022

Sustainability

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Refracturing can alleviate the rapid decline of shale gas production with a low drilling cost, but an appropriate fracture layout and optimal refracturing time have been unclear without a heavy computation load. This paper proposes a combination approach with a numerical simulation and data-driven analysis to quickly evaluate the impacts of the refracturing layout and refracturing time on shale gas production. Firstly, a multiphysical coupling model with the creep of natural fractures is established for the numerical simulation on shale gas production. Secondly, the effects of the refracturing layout and refracturing time on the shale gas production are investigated through a single factor sensitivity analysis, but this analysis cannot identify the fracture interaction. Thirdly, the influence of fractures interaction on shale gas production is explored through a combination of a global sensitivity analysis (GSA) and an artificial neural network (ANN). The GSA results observed that the adjacent fractures have more salient interferences, which means that a denser fracture network will not significantly increase the total gas production, or will reduce the contribution from each fracture, resulting in higher fracturing costs. The new fractures that are far from existing fractures have greater contributions to cumulative gas production. In addition, the optimal refracturing time varies with the refracturing layout and is optimally implemented within 2–3 years. A suitable refracturing scale and time should be selected, based on the remaining gas reserve. These results can provide reasonable insights for the refracturing design on the refracturing layout and optimal time. This ANN-GSA approach provides a fast evaluation for the optimization of the refracturing layout and time without enormous numerical simulations.

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“…Moosavi et al [41] thought that in the whole stress-strain process, the permeability varied in different ways in the elastic stage, the elastic-plastic stage, and the residual flow stage due to the different deformation degrees of rock samples. Killough et al [42], Agheshlui et al [43], and Lu et al [44] constructed single function mathematical models such as cubic polynomial, logarithmic function, and power function of confining pressure and permeability, respectively. Many studies have focused on the variations, influence mechanisms, and mathematical models of the relationship between rock permeability and stress.…”

Section: Introductionmentioning

confidence: 99%

Experimental Study on Relative Permeability Characteristics for CO2 in Sandstone under High Temperature and Overburden Pressure

et al. 2021

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In this study, CO2 seepage of sandstone samples from the Taiyuan-Shanxi Formation coal seam roof in Ordos Basin, China, under temperature-stress coupling was studied with the aid of the TAWD-2000 coal rock mechanics-seepage test system. Furthermore, the evolution law and influencing factors on permeability for CO2 in sandstone samples with temperature and axial pressure were systematically analyzed. The results disclose that the permeability of sandstone decreases with the increase in stress. The lower the stress is, the more sensitive the permeability is to stress variation. High stress results in a decrease in permeability, and when the sample is about to fail, the permeability surges. The permeability of sandstone falls first and then rises with the rise of temperature, which is caused by the coupling among the thermal expansion of sandstone, the desorption of CO2, and the evaporation of residual water in fractures. Finally, a quadratic function mathematical model with a fitting degree of 98.2% was constructed between the temperature-stress coupling effect and the permeability for CO2 in sandstone. The model provides necessary data support for subsequent numerical calculation and practical engineering application. The experimental study on the permeability characteristics for CO2 in sandstone under high temperature and overburden pressure is crucial for evaluating the storage potential and predicting the CO2 migration evolution in underground coal gasification coupling CO2 storage projects.

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Investigating the effects of stress creep and effective stress coefficient on stress-dependent permeability measurements of shale rock

Cited by 15 publications

References 16 publications

Triaxial testing on water permeability evolution of fractured shale

Triaxial testing on water permeability evolution of fractured shale

A Combination Approach of the Numerical Simulation and Data-Driven Analysis for the Impacts of Refracturing Layout and Time on Shale Gas Production

Experimental Study on Relative Permeability Characteristics for CO2 in Sandstone under High Temperature and Overburden Pressure

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