Apparent permeability model for gas transport through micropores and microfractures in shale reservoirs

Gao, Qi; Han, Sen; Cheng, Yuanfang; Li, Yang; Yan, Cheng; Han, Zhongying

doi:10.1016/j.fuel.2020.119086

Cited by 50 publications

(57 citation statements)

References 55 publications

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“…Fig. 2 Different gas flow regimes in coal matrix (Gao et al 2021) flow regimes can be determined by the Knudsen number Kn, which is calculated by the ratio of the molecules mean free path to the pore diameter (Beskok and Karniadakis 1999). For the gas flow in micropores, Beskok and Karniadakis (1999) proposed a unified model that can predict mass flow rate for channel under the entire flow range (0 < Kn < ∞).…”

Section: Knudsen Diffusionmentioning

confidence: 99%

“…But the effective stress effect, real gas effect and multiple gas flow mechanisms are ignored. Further, Gao et al (2021) comprehensively considered these important factors to develop the permeability model, while the effects of tortuosity of micropores and microfractures on gas flow were neglected. In order to improve the previous permeability models and predict the permeability accurately, all the above important factors mentioned are both considered in our new present model.…”

Section: Total Fractal Permeability Model Of Cbm Reservoirmentioning

confidence: 99%

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A Fractal Permeability Model for Gas Transport in the Dual-Porosity Media of the Coalbed Methane Reservoir

et al. 2021

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In the process of coalbed methane (CBM) exploitation, permeability is a key controlling parameter for gas transport in the CBM reservoirs. The CBM reservoir contains a large number of micropores and microfractures with complex structures. In order to accurately predict the gas permeability of the micropores and microfractures in CBM reservoirs, a fractal permeability model was developed in this work. This model considers the comprehensive effects of real gas, stress dependence, multiple gas flow mechanisms (e.g., slip flow, Knudsen diffusion and surface diffusion) and fractal characteristics (e.g., pore size distribution and flow path tortuosity) of micropores and microfractures on the gas permeability. Then, this fractal permeability model was verified by the reliable experimental data and other theoretical models. Finally, the sensitivity analysis is conducted to identify key factors to the permeability of CBM reservoir. The results showed that the fractal characteristics of the micropores and microfractures have significant effects on the permeability of CBM reservoir. Higher fractal dimension of micropores diameter and microfractures aperture represents the larger number of micropores and microfractures, resulting in a higher permeability. Higher tortuosity fractal dimension of micropores and microfractures means higher gas flow resistance, leading to the lower permeability. The multiple gas transport mechanisms coexist in micropores and microfractures of CBM reservoir. The permeability of slip flow and Knudsen diffusion both increases with the decrease in pore pressure. Surface diffusion is an important gas transport mechanisms in micropores, but it can be ignored in the microfractures. Knudsen diffusion plays a more obvious role in the lower pore pressure, which controls the gas transport in microfractures. And microfractures are beneficial to improve gas transport capacity of coalbed methane reservoir.

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Section: Knudsen Diffusionmentioning

confidence: 99%

Section: Total Fractal Permeability Model Of Cbm Reservoirmentioning

confidence: 99%

A Fractal Permeability Model for Gas Transport in the Dual-Porosity Media of the Coalbed Methane Reservoir

et al. 2021

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“…In addition, it can be found that the actual effective stress has a good power function relationship with the permeability variation in the selected range. In the initial stage, the microfractures in the rock are gradually closed with the increase of effective stress, which leads to the partial loss of the main contribution to induce permeability [3]. In the later stage of effective stress increase, elasticplastic deformation mainly occurs in the shale rock, and the shale framework particles might change.…”

Section: Effect Of Internal Microfracture On Pressure-dependentmentioning

confidence: 99%

“…It is well known that shale gas reservoirs are rich in nanomicron pores with low porosity and ultralow permeability [1][2][3]. In recent years, the successful experience of shale gas reservoir exploitation has shown that fracturing, especially stimulated reservoir volume (SRV), is an effective means to achieve effective production of shale gas reservoirs [4,5].…”

Section: Introductionmentioning

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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“…Different from conventional hydrocarbon reservoirs, shale reservoirs with low porosity and extralow permeability contain abundant nanopores [3][4][5][6], which significantly control the storage and seepage capacity of shale reservoirs [7]. Therefore, it is quite meaningful to characterize shale pore structure, such as pore shape, pore size, and pore connectiv-ity [8]. Many advanced technologies have been applied in shale pore structure characterization [9][10][11], such as imaging method (scanning electron microscopy, micro-nano CT, atomic force microscopy, etc.…”

Section: Introductionmentioning

confidence: 99%

Effect of Shale Sample Particle Size on Pore Structure Obtained from High Pressure Mercury Intrusion Porosimetry

Gao

Duan

et al. 2021

Geofluids

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With the rapid development of unconventional oil and gas, the pore structure characterization of shale reservoirs has attracted an increasing attention. High pressure mercury intrusion porosimetry (HPMIP) has been widely used to quantitatively characterize the pore structure of tight shales. However, the pore structure obtained from HPMIP could be significantly affected by the sample particle size used for the analyses. This study mainly investigates the influence of shale sample particle size on the pore structure obtained from HPMIP, using Mississippian-aged Barnett Shale samples. The results show that the porosity of Barnett Shale samples with different particle sizes obtained from HPMIP has an exponentially increasing relation with the particle size, which is mainly caused by the new pores or fractures created during shale crushing process as well as the increasing exposure of blind or closed pores. The amount and proportion of mercury retention during mercury extrusion process increase with the decrease of shale particle size, which is closely related to the increased ink-bottle effect in shale sample with smaller particle size. In addition, the fractal dimension of Barnett Shale is positively related to the particle size, which indicates that the heterogeneity of pore structure is stronger in shale sample with larger particle size. Furthermore, the skeletal density of shale sample increases with the decrease of particle size, which is possibly caused by the differentiation of mineral composition during shale crushing process.

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Apparent permeability model for gas transport through micropores and microfractures in shale reservoirs

Cited by 50 publications

References 55 publications

A Fractal Permeability Model for Gas Transport in the Dual-Porosity Media of the Coalbed Methane Reservoir

A Fractal Permeability Model for Gas Transport in the Dual-Porosity Media of the Coalbed Methane Reservoir

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

Effect of Shale Sample Particle Size on Pore Structure Obtained from High Pressure Mercury Intrusion Porosimetry

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