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.

scholarly journals Reservoir Permeability Evolution during the Process of CO2-Enhanced Coalbed Methane Recovery

Energies ◽  
2018 ◽  
Vol 11 (11) ◽  
pp. 2996 ◽  
Author(s):  
Gang Wang ◽  
Ke Wang ◽  
Yujing Jiang ◽  
Shugang Wang
Keyword(s):  
Effective Stress ◽  
Coalbed Methane ◽  
Volumetric Strain ◽  
Fracture Aperture ◽  
Permeability Evolution ◽  
Methane Recovery ◽  
Permeability Model ◽  
Reservoir Permeability ◽  
Stress Changes ◽  
Enhanced Coalbed Methane

In this study, we have built a dual porosity/permeability model through accurately expressing the volumetric strain of matrix and fracture from a three-dimensional method which aims to reveal the reservoir permeability evolution during the process of CO2-enhanced coalbed methane (CO2-ECBM) recovery. This model has accommodated the key competing processes of mechanical deformation and adsorption/desorption induced swelling/shrinkage, and it also considered the effect of fracture aperture and effective stress difference between each medium (fracture and matrix). We then numerically solve the permeability model using a group of multi-field coupling equations with the finite element method (FEM) to understand how permeability evolves temporally and spatially. We further conduct multifaceted analyses to reveal that permeability evolution near the wells is the most dramatic. This study shows that the farther away from the well, the gentler the evolution of permeability. The evolution of reservoir permeability near the injection well (IW) and the production well (PW) are very different, due to the combined effects of effective stress changes and gas adsorption and desorption. Furthermore, adsorption is the main controlling factor for the change of permeability for regions near the IW, while the change in effective stress is the main cause for the change in permeability near the PW. Increasing the injection pressure of CO2 will cause the reservoir permeability to evolve more quickly and dynamically.

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.

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 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.

A water permeability model of nano-reinforced cement pastes based on GEM theory and multifractals

2021 ◽  
pp. 1-24
Author(s):  
Yuan Gao ◽  
Hongwen Jing ◽  
Zefu Zhou ◽  
Xinshuai Shi ◽  
Zhenlong Zhao
Keyword(s):  
Water Permeability ◽  
Permeability Model ◽  
Cement Pastes ◽  
Reinforced Cement

scholarly journals Stress-Dependent Permeability of Fractures in Tight Reservoirs

Energies ◽  
2018 ◽  
Vol 12 (1) ◽  
pp. 117 ◽  
Author(s):  
Nai Cao ◽  
Gang Lei ◽  
Pingchuan Dong ◽  
Hong Li ◽  
Zisen Wu ◽  
...  
Keyword(s):  
Effective Stress ◽  
Influencing Factor ◽  
Quantitative Model ◽  
Stress Sensitivity ◽  
Gas Production ◽  
Fracture System ◽  
Permeability Model ◽  
Fracture Systems ◽  
Tight Reservoirs ◽  
Stress Dependent

Permeability is one of the key factors involved in the optimization of oil and gas production in fractured porous media. Understanding the loss in permeability influenced by the fracture system due to the increasing effective stress aids to improve recovery in tight reservoirs. Specifically, the impacts on permeability loss caused by different fracture parameters are not yet clearly understood. The principal aim of this paper is to develop a reasonable and meaningful quantitative model that manifests the controls on the permeability of fracture systems with different extents of fracture penetration. The stress-dependent permeability of a fracture system was studied through physical tests and numerical simulation with the finite element method (FEM). In addition, to extend capability beyond the existing model, a theoretical stress-dependent permeability model is proposed with fracture penetration extent as an influencing factor. The results presented include (1) a friendly agreement between the predicted permeability reduction under different stress conditions and the practical experimental data; (2) rock permeability of cores with fractures first reduces dramatically due to the closure of the fractures, then the permeability decreases gradually with the increase in effective stress; and (3) fracture penetration extent is one of the main factors in permeability stress sensitivity. The sensitivity is more influenced by fracture systems with a larger fracture penetration extent, whereas matrix compaction is the leading influencing factor in permeability stress sensitivity for fracture systems with smaller fracture penetration extents.

scholarly journals Failure and Seepage Characteristics of Gas-Bearing Coal under Accelerated Loading and Unloading Conditions

2019 ◽  
Vol 9 (23) ◽  
pp. 5141
Author(s):  
Zhang ◽  
Wang ◽  
Du ◽  
Lou ◽  
Wang
Keyword(s):  
Confining Pressure ◽  
In Situ Stress ◽  
Permeability Evolution ◽  
Permeability Model ◽  
Significant Control ◽  
Gas Dynamic ◽  
Working Face ◽  
Loading And Unloading ◽  
Seepage Characteristics ◽  
Gas Bearing

In actual mining situations, the advancing speed of the working face is usually accelerated, which may affect the failure and seepage characteristics of gas-bearing coal, and may even induce dynamic disasters. In order to discover the effects of such accelerated advancement of the working face, an experimental study on the failure and seepage characteristics of gas-bearing coal under accelerated loading and unloading conditions was carried out in this work. The results showed that the energy release was more violent and impactful under accelerated loading and unloading paths. The time required for the failure of the sample was significantly shortened. After being destroyed, the breakup of the sample was more severe, and the magnitude of the permeability was greater. Accordingly, the acceleration of the loading and unloading had significant control effects on the failure and permeability of coal and it showed a significant danger of inducing coal and gas dynamic disasters. Meanwhile, the degree of influence of the acceleration on the coal decreased with an increase in the gas pressure and increased significantly with an increase in the initial confining pressure. It was found that for a deep high-gas mine, the accelerated advancement of the working face under a high in situ stress condition would greatly increase the risk of coal and gas dynamic disasters. Then, the permeability evolution model of gas-bearing coal in consideration of changes in the loading and unloading rates was theoretically established in this work, and this permeability model was validated by experimental data. The permeability model was found to be relatively reasonable. In summary, the effects of accelerated loading and unloading on the failure and seepage characteristics of gas-bearing coal were obtained through a combination of experimental and theoretical studies, and the intrinsic relationship between the accelerated advancement of the working face and the occurrence of coal and gas dynamic disasters was discovered in this work.

scholarly journals Thermomechanical Behavior of Late Indo-Chinese Granodiorite under High Temperature and Pressure

2018 ◽  
Vol 2018 ◽  
pp. 1-15
Author(s):  
Yanjun Zhang ◽  
Shuren Hao ◽  
Lin Bai ◽  
Ziwang Yu ◽  
Jianing Zhang ◽  
...  
Keyword(s):  
Bulk Modulus ◽  
Effective Stress ◽  
Triaxial Compression ◽  
Rock Fracture ◽  
Geothermal System ◽  
Reservoir Rocks ◽  
Biot’S Coefficient ◽  
Wide Range ◽  
Simulation Calculation ◽  
Temperature And Pressure

This study investigates the influence of temperature, effective stress, and rock fracture on the bulk modulus and Biot’s coefficient of granodiorite from a hot dry rock geothermal reservoir using the triaxial compression test. Three types of representative granodiorite samples were chosen for comparative experiments. The experiments were conducted with 0–55 MPa effective stress under cyclic loading. Results show that bulk modulus can continuously increase with the increase in effective stress at a constant temperature. The influencing law on Biot’s coefficient is opposite that on bulk modulus. Interestingly, the temperature effects on the drained bulk modulus and Biot’s coefficient depend on the effective stress. With regard to rock fractures, temperature and effective stress exert similar effects on the Biot’s coefficients and bulk moduli of the samples compared with those of intact rock. The data of this experiment have a wide range of applications because most of the reservoir rocks in dry-hot-rock geothermal system have lithology of granite or granodiorite. The change law of rock modulus and Biot’s coefficient with the temperature and pressure in this experiment provide the data basis for the future simulation calculation making the considered factors more comprehensive and the results closer to the real situation.

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