Experimental Observations of Gas-sorption-Induced Strain Gradients and their Implications on Permeability Evolution of Shale

Shi, Rui; Liu, Jishan; Wang, Xiaoming; Elsworth, Derek; Wang, Zhizhuang; Wei, Mingyao; Cui, Guanglei

doi:10.1007/s00603-021-02473-4

Cited by 14 publications

(11 citation statements)

References 76 publications

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“…During the experiment, adsorptive gas is injected into the high-pressure chamber until the anticipated pressure is reached. Then, the bulk swelling strain of shale sample is directly measured by the attached strain gauges when gas pressure inside the chamber is stabilized. ,, The measured bulk swelling strain actually consists of two components. One component is the swelling strain purely induced by gas adsorption.…”

Section: Challenges and Perspectivesmentioning

confidence: 99%

“…Due to this naturally huge permeability contrast, it may take several months or even a few years for shale to reach the ultimate equilibrium state as gas diffusion from the fracture wall into the shale matrix is a very slow process. This transient process will induce a nonuniform pore pressure distribution in the shale matrix, and thus the induced swelling strain is time-dependent and nonuniform as well. , Under this condition, shale permeability evolution behaviors become much more complex and cannot be explained by the models as summarized in Table . Thus, current experimental and theoretical approaches should be redesigned to capture the time-dependent behaviors of swelling strain and permeability evolution in fractured shale.…”

Section: Challenges and Perspectivesmentioning

confidence: 99%

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A Review of Swelling Effect on Shale Permeability: Assessments and Perspectives

et al. 2023

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The significant effect of gas sorption induced swelling on shale permeability has been observed through laboratory measurements and explained through permeability models over the past decades. However, there are lab observations that cannot be explained by these models. This knowledge gap prompts this review. Our goal is to form perspectives on how to resolve this gap through assessing the role of swelling on shale permeability. This goal is achieved through the following three steps: (1) collection of experimental shale permeability data measured under both constant effective stress and constant confining pressure conditions; (2) collection and classification of shale permeability models under the influence of gas sorption induced swelling strains; (3) assessments of co-relations between shale permeability data and permeability models. On the basis of all assessments, we conclude that the discrepancies between model predictions and laboratory measurements depend on the relation between bulk and pore swelling strains, pore size scales, and consistencies of strain treatments in the experiments and models. Models assuming that bulk swelling strain is different from pore swelling strain can better explain lab observations than those assuming that they are the same. When the pore size transitions from the micron-scale to the nano-scale, the effect of swelling on shale permeability gradually diminishes. The inconsistencies between how swelling strains are measured in the lab and treated in the models are common in the literatures and affect the discrepancies between model predictions and lab observations. On the basis of these assessments, we form our perspectives: (1) transformation between bulk and pore swelling strains should be characterized and incorporated both for experiments and in permeability models; (2) shale multiscale pore structural characteristics should be characterized when assessing the swelling effect on shale permeability; (3) the time-dependent nature of swelling strain and permeability evolution should be incorporated into future experiments and permeability models.

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Section: Challenges and Perspectivesmentioning

confidence: 99%

Section: Challenges and Perspectivesmentioning

confidence: 99%

A Review of Swelling Effect on Shale Permeability: Assessments and Perspectives

et al. 2023

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“…17−19 This means that during gas production, shale is mainly in nonequilibrium states. 6,8,20,21 During nonequilibrium periods, matrix pressure exhibits a nonuniform distribution from the fracture wall to the inner matrix. 17,20,22 In addition, under the influence of environmental conditions, geological history, and chemical reactions during formation, the shale matrix comprises multiple minerals, which can broadly be classified into organic matter (kerogen inclusions) and inorganic matrix (including clay, quartz, and pyrite).…”

Section: Introductionmentioning

confidence: 99%

Shale Gas Production Evaluation Considering Gas Diffusion and Dispersed Distribution of Kerogen

Huang,

Liu,

Gao

et al. 2023

Energy Fuels

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In the shale matrix, organic matter (kerogen) is dispersed and embedded within an inorganic matrix, and its internal gas diffusion is a long-term process. Under the influence of the transient process and complex structure, pressure and Langmuir's strain constant in the matrix are typically distributed nonuniformly. This implies that the sorption-induced swelling/shrinkage in the matrix would also present a nonuniform distribution, and the resulting matrix−fracture mechanical interactions have significant impacts on gas flow in shale fractures as well as gas production. In this study, through the concepts of the swelling path and swelling triangle, the nonuniform swelling/shrinkage is characterized, thereby establishing the relationship between shale response and swelling/shrinkage behaviors. In addition, given that gas transport in organic and inorganic matrixes is typically governed by different mechanisms, the influence of the compositional heterogeneity on gas flow in the matrix is also investigated. Subsequently, novel shale permeability and gas flow models are developed, incorporating the effects of gas diffusion and the dispersed distribution of kerogen. The proposed concepts and developed models are validated by comparing simulation results with one set of experimental observations, as well as two sets of field production data. Our results suggest that neglecting the mechanisms induced by the transient process and complex structure would lead to inaccurate estimations of shale permeability during gas production and result in underestimations of both gas production rates and cumulative production.

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Section: Introductionmentioning

confidence: 99%

“…The Brazilian splitting method is used to create microfractures in shale, and shale samples containing natural fractures are used to study the change law of the gas permeability in the fractures. − The permeability of shale fractures is affected by the effective stress along different paths. ,, The internal pressure remains unchanged, and the increase in the external pressure can help effectively reduce the permeability of shale fractures. ,, The relationship between the effective stress and shale fracture permeability can be characterized using the exponential model and power model. ,− In addition to the effective stress, the permeability of shale fractures is affected by the external temperature , and gas adsorption characteristics. , The fracture characteristics of the shale itself cannot be ignored. The fracture conductivity is positively correlated with the penetration and opening of fractures. ,,− The permeability of shale fractures is affected by the roughness and tortuosity of the fractures and also by the gas slippage phenomenon. − As a result, the measured permeability is greater than the actual value.…”

Section: Introductionmentioning

confidence: 99%

Experimental Study on the Effects of Pore Pressure and Slippage on the Permeability of a Fracture Network during Depressurization of Shale Gas Reservoir Production

Zhao

Sun

et al. 2022

ACS Omega

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Hydraulic fracturing technology is an important technical means to increase shale gas production. The seepage channels formed in the hydraulic fractures during hydraulic fracturing can help increase reservoir permeability. Therefore, it is of significance to study the seepage law of the fracture network after reservoir hydraulic fracturing. In this study, hydraulic fracturing is used to fracture full-diameter shale cores, and three typical forms of hydraulic fracture networks are obtained. The characteristics of the fracture networks are analyzed by X-ray CT scanning. The effects of pore pressure and slippage on the permeability of the fracture networks are simulated by conducting experiments. The experimental results show that in the direction of gas seepage, hydraulic fractures completely penetrate the sample, and the greater the diameter and volume of the fracture, the better the hydraulic fracture conductivity. When the confining pressure remains unchanged at 50 MPa, the apparent permeability values of the hydraulic fractures with the worst and best fracture morphologies increase by 44.4 times and 2.8 times, respectively, with the decrease in the pore pressure from 30 to 2 MPa. The apparent permeability of the shale samples has a power function relationship with the pore pressure. The test results also show that the absolute permeability is positively correlated with the number of effective seepage channels in the hydraulic fractures and the number of hydraulic fractures, whereas the Klinkenberg coefficient is negatively correlated. Our research results can provide a basis for shale gas production model research and for on-site production capacity improvement. The qualitative understanding and scientific explanation of the effects of pore pressure and slippage on fracture network permeability in the process of depressurization of reservoir production have been realized.

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Experimental Observations of Gas-sorption-Induced Strain Gradients and their Implications on Permeability Evolution of Shale

Cited by 14 publications

References 76 publications

A Review of Swelling Effect on Shale Permeability: Assessments and Perspectives

A Review of Swelling Effect on Shale Permeability: Assessments and Perspectives

Shale Gas Production Evaluation Considering Gas Diffusion and Dispersed Distribution of Kerogen

Experimental Study on the Effects of Pore Pressure and Slippage on the Permeability of a Fracture Network during Depressurization of Shale Gas Reservoir Production

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