An experimental investigation of the nonlinear gas flow and stress‐dependent permeability of shale fractures

Shen, Zhikang; Zhou, Lei; Su, Xiaopeng; Li, Honglian; Tang, Jiren; Zheng, Xiaowei

doi:10.1002/ese3.696

Cited by 7 publications

(5 citation statements)

References 37 publications

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“…When the influence of fracture structure is considered, the effective stress can be taken as the macroscopic average for the fractured rock mass, and the effective stress coefficient α can be regarded as 1 for simplicity. The gas flow pressure in the fracture can be regarded as the average of the inlet pressure and outlet pressure [22],…”

Section: Test Schemementioning

confidence: 99%

“…The existing literature is mostly focused on nonlinear fluid seepage through fractured rock masses in sandstone, shale, and marble, whereas seepage in rough fractures in coal is rarely studied in terms of the influence of fracture structure, environmental factors, and fluid properties. In addition, field tests, laboratory tests, and simulations have found that the nonlinear aspects of flows can be described by the Forchheimer equation [18] and Izbash equation [19], but the scope of application of both has not been clarified [20][21][22].…”

Section: Introductionmentioning

confidence: 99%

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An Experimental Study on the Seepage Characteristics of Rough Fractures in Coal under Stress Loading

Luo,

Zhu,

Huang

2024

Processes

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Fracture and stress environments significantly affect the flow of coalbed methane. Under stress, fracture deformation and damage occur, which change the original fracture characteristics and lead to changes in gas flow characteristics. The change in gas pressure gradient makes the fluid flow obviously nonlinear. Using linear flow theory to describe the fracture flow leads to a large error in predicting coalbed methane productivity. In this study, seepage tests on fractured coal are carried out under different stresses and gas pressure gradients, the nonlinear flow and changes in related parameters are analyzed, and the applicability of the nonlinear flow equation is evaluated. The resulting seepage of the gas flow in the fracture under stress is obviously nonlinear, which gradually increases with increasing effective stress and gas pressure gradient. When the Forchheimer equation is used to characterize the nonlinear seepage in fractures, the coefficients increase with increasing effective stress. The permeability, nonlinear factor, and critical Reynolds number decrease with increasing effective stress. When the Izbash equation is used for this case, the linear coefficient ranges from 1015 to 1016, and the nonlinear coefficient ranges from 1.064 to 1.795. The coefficients are related to the effective stress through a power function. Both the Forchheimer and Izbash equations can characterize the flow in rough fractures in coal during stress loading. However, the Forchheimer equation better reveals the mechanism of flow transformation from linear to nonlinear in fractures.

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Section: Test Schemementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

An Experimental Study on the Seepage Characteristics of Rough Fractures in Coal under Stress Loading

Luo,

Zhu,

Huang

2024

Processes

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“…The seepage characteristic curves of shale with different fracture widths are shown in Figure 4(b). Similarly, the smaller the fracture width, the more the seepage curve deviates from the origin, and the more obvious its nonlinear permeability characteristics [29]. The main reason is that the fracture width alters the seepage volume of shale rock, while the seepage trajectory is the extended by fracture length.…”

Section: Effect Of Internal Microfracture Width On Seepagementioning

confidence: 99%

Experimental Research of the Influence of Microfracture Morphology on Permeability of Shale Rock

et al. 2021

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Hydraulic fracturing is currently one of the main technical methods of shale gas exploitation. The permeability variation of shale gas reservoir after fracturing is inevitable, while the influence of fracture length and fracture width on permeability and seepage characteristics of shale rock is a mystery. Besides, the stress sensitivity characteristics of shale rock, derived from different initial permeability, with the same permeability after fracturing are also ambiguous. To this end, a series of seepage characteristic experiments related to different fracture parameters are carried out with the black shale of the Longmaxi Formation in Sichuan gas field as the research target. The results show that the fracture length and fracture width have a good exponential relationship with the corresponding permeability of the reformed shale rock, and the contribution of the fracture width to shale permeability is much greater than that of the fracture length. In addition, the nonlinear seepage characteristics of shale rock are gradually significant with the reduction of fracture length and fracture width. Taking the primitive effective stress (10 MPa) as a critical point, the permeability of shale with large initial permeability decreased by 26.4%, which is about twice as much as that of shale rock with small initial permeability (14.9%) in the selected pressure loading stage, owing to the difference of fracture width inside the shale rock. The permeability of the shale rock with a large initial permeability is restored by 14.7%, while the shale rock with a small initial permeability is only recovered to 5.2% in the pressure unloading stage, which is attributed to the closure of fractures, especially the loss of fracture width. This research can provide some new insights for the production prediction of shale gas reservoir after fracturing.

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“…The result indicated that the smaller the effective stress (Boit) coefficient obtained by the experiment is, the stronger is the exponential relationship between the permeability and the effective stress, and the stronger is the stress sensitivity of the shale. Shen et al 9 found that the permeability sensitivity of shale fractures under stress was very strong, and the exponential relationship better described the pressure dependency of the permeability for the tested shale samples. For high‐pressure deep shale gas reservoirs, which ware usually highly stress‐sensitive, the impact of strong stress sensitivity should be fully considered 10 .…”

Section: Introductionmentioning

confidence: 97%

Numerical simulation study on the mechanical behavior of shale core and reservoir rock mass

Xiong

et al. 2020

Energy Science & Engineering

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After the hydraulic fracturing of the shale reservoir, the stress field changes during the mining process. The stress sensitivity of the reservoir affects its development capabilities. Moreover, the stress sensitivity of shale reservoirs obtained by various researchers using different experimental methods is not uniform. This study analyzes the physical background differences between reservoir rock mass and experimental core. In this study, we establish the “support structure model” of the reservoir and show that the reservoir rock body has a structural overall effect, such that the supporting effect of the surrounding rock on the overlying strata is very strong. At the same time, we also establish the transverse isotropic numerical model of the shale reservoir on the basis of the real physical background of the reservoir and the experimental physical core model on the basis of the real physical background of the core test. This study shows that the equivalent mechanical behavior of the core test in the holder is pure core compression without the support and pull of the whole rock mass structure. In the real reservoir, the reservoir rock mass has significant structural effect. The actual compression change of real reservoir mining is less than the pure compression displacement of the experimental test core. The core stress sensitivity of the conventional experimental test does not directly describe the true stress‐strain effect of the macroscopic reservoir rock mass as a structural whole. A laboratory stress‐sensitive test apparatus and method that is equivalent to the physical background of a real reservoir needs to be improved or designed.

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An experimental investigation of the nonlinear gas flow and stress‐dependent permeability of shale fractures

Cited by 7 publications

References 37 publications

An Experimental Study on the Seepage Characteristics of Rough Fractures in Coal under Stress Loading

An Experimental Study on the Seepage Characteristics of Rough Fractures in Coal under Stress Loading

Experimental Research of the Influence of Microfracture Morphology on Permeability of Shale Rock

Numerical simulation study on the mechanical behavior of shale core and reservoir rock mass

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