Review on gas flow and recovery in unconventional porous rocks

Lin, Duanlin; Wang, Jinjie; Yuan, Bin; Shen, Yinghao

doi:10.26804/ager.2017.01.04

Cited by 51 publications

(20 citation statements)

References 71 publications

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“…Knudsen diffusion is another important transport mechanism in nanometer pores [55][56][57][58]. Considering solid surface roughness [18,59], we can express Knudsen diffusion in the following form:…”

Section: Knudsen Diffusionmentioning

confidence: 99%

Gas Transport Model in Organic Shale Nanopores Considering Langmuir Slip Conditions and Diffusion: Pore Confinement, Real Gas, and Geomechanical Effects

et al. 2018

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Nanopores are extremely developed and randomly distributed in shale gas reservoirs. Due to the rarefied conditions in shale strata, multiple gas transport mechanisms coexist and need further understanding. The commonly used slip models are mostly based on Maxwell slip boundary condition, which assumes elastic collisions between gas molecules and solid surfaces. However, gas molecules do not rebound from solid surfaces elastically, but rather are adsorbed on them and then re-emitted after some time lag. A Langmuir slip permeability model was established by introducing Langmuir slip BC. Knudsen diffusion of bulk phase gas and surface diffusion of adsorbed gas were also coupled into our nanopore transport model. Considering the effects of real gas, stress dependence, thermodynamic phase changes due to pore confinement, surface roughness, gas molecular volume, and pore enlargement due to gas desorption during depressurization, a unified gas transport model in organic shale nanopores was established, which was then upscaled by coupling effective porosity and tortuosity to describe practical SGR properties. The bulk phase transport model, single capillary model, and upscaled porous media model were validated by data from experimental data, lattice Boltzmann method or model comparisons. Based on the new gas transport model, the equivalent permeability of different flow mechanisms as well as the flux proportion of each mechanism to total flow rate was investigated in different pore radius and pressure conditions. The study in this paper revealed special gas transport characteristics in shale nonopores and provided a robust foundation for accurate simulation of shale gas production.

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Section: Knudsen Diffusionmentioning

confidence: 99%

Gas Transport Model in Organic Shale Nanopores Considering Langmuir Slip Conditions and Diffusion: Pore Confinement, Real Gas, and Geomechanical Effects

et al. 2018

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“…22 Fractal theory is powerful in studying the imbibition in complex porous media. [23][24][25] Fractal structure parameters are considered to explore the spontaneous imbibition into a fractal tree-like network, 26 and the influences of tortuosity, asymmetry, and wettability on capillary rise are investigated based on fractal theory. 27 Also, fractal theory is helpful for permeability evaluation in rock fracture networks.…”

Section: Introductionmentioning

confidence: 99%

Spontaneous Imbibition Process in Micro–nano Fractal Capillaries Considering Slip Flow

Shen

et al. 2018

Fractals

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An imbibition process of water into a matrix is required to investigate the influences of large-volume fracturing fluids on gas production of unconventional formations. Slip flow has been recognized by recent studies as a major mechanism of fluid transport in nanotubes. For nanopores in shale, a slip boundary is nonnegligible in the imbibition process. In this study, we established an analytic equation of spontaneous imbibition considering slip effects in capillaries. A spontaneous imbibition model that couples the analytic equation considering the slip effect was constructed based on fractal theory. We then used a model for various conditions, such as slip boundary, pore structure, and fractal dimension of pore tortuosity, to capture the imbibition characteristics considering the slip effect. A dynamic contact angle was integrated into the modeling. Results of our study verify that the slip boundary influences water imbibition significantly. The imbibition speed is significantly improved when slip length reaches the equivalent diameter of a tube. Therefore, disregarding the slip effect will underestimate the imbibition speed in shale samples.

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“…[1][2][3][4][5][6][7][8][9][10] At present, North America is the only region in the world where commercial exploitation of tight oil is widespread. The output of tight oil in the United States (US) has soared since 2006, by 2012, the production of tight oil accounted for 29% of the total output of US oil and gas, which successfully reversed the situation in the US of a production decline lasting 24 years.…”

Section: Introductionmentioning

confidence: 99%

Fractal Nature of Porosity in Volcanic Tight Reservoirs of the Santanghu Basin and Its Relationship to Pore Formation Processes

Wang

Chen

et al. 2018

Fractals

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In this paper, in a case study of Santanghu Basin in China, the morphological characteristics and size distribution of nanoscale pores in the volcanic rocks of the Haerjiawu Formation were investigated using the results of low temperature nitrogen adsorption experiments. This research showed that within the target layer, a large number of nanoscale, eroded pores showed an "ink bottle" morphology with narrow pore mouths and wide bodies. The fractal dimension of pores increases gradually with increasing depth. Moreover, as fractal dimension increases, BET-specific surface area gradually increases, average pore diameter decreases and total pore volume gradually increases. The deeper burial of the Haerjiawu volcanic rocks in the Santanghu Basin leads to more intense erosion by organic acids derived from the basin's source rocks. Furthermore, the internal surface roughness of these corrosion pores results in poor connectivity. As stated above, the corrosion process is directly related to the organic acids generated by the source rock of the interbedded volcanic rocks. The deeper the reservoir, the more the organic acids being released from the source rock. However, due to the fact that the Haerjiawu volcanic rocks are tight reservoirs and have complicated pore-throat systems, while organic acids dissolve unstable minerals such as feldspars which improve the effective reservoir space; the dissolution of feldspars results in the formation of new minerals, which cannot be expelled from the tight reservoirs. They are instead precipitated in the fine pore throats, thereby reducing pore connectivity, while enhancing reservoir micro-preservation conditions.

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Review on gas flow and recovery in unconventional porous rocks

Cited by 51 publications

References 71 publications

Gas Transport Model in Organic Shale Nanopores Considering Langmuir Slip Conditions and Diffusion: Pore Confinement, Real Gas, and Geomechanical Effects

Gas Transport Model in Organic Shale Nanopores Considering Langmuir Slip Conditions and Diffusion: Pore Confinement, Real Gas, and Geomechanical Effects

Spontaneous Imbibition Process in Micro–nano Fractal Capillaries Considering Slip Flow

Fractal Nature of Porosity in Volcanic Tight Reservoirs of the Santanghu Basin and Its Relationship to Pore Formation Processes

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