Pore Networks and Fluid Flow in Gas Shales

Wang, Fred P.; Reed, Rob M.

doi:10.2118/124253-ms

Cited by 366 publications

(227 citation statements)

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“…The pore structures of shale are highly heterogeneous, with the pore size mainly ranging from nanometer to micrometer-sized [5,6]. Previous research has reported that nanometer-sized pores, which are predominantly associated with organic matter and clay minerals [6][7][8], could provide larger surface areas and higher adsorption energy for gas molecule adsorption [9][10][11][12], while micrometer-sized pores-which are generally associated with inorganic minerals [6]-are more likely to connect with induced fractures for gas flow and transport [13,14]. For gas desorption, once external conditions, such as temperature and pressure changes, for example, and artificial fractures disturb the equilibrium, the free gas molecules in fractures and macropore networks flow from high-pressure zones to low-pressure zones, and then gas that adsorbed onto the surface of organic matter and clay minerals starts to desorb, inducing a concentration gradient between the bulk particles and their surface.…”

Section: Introductionmentioning

confidence: 99%

Methane Adsorption Rate and Diffusion Characteristics in Marine Shale Samples from Yangtze Platform, South China

et al. 2017

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Knowledge of the gas adsorption rate and diffusion characteristics in shale are very important to evaluate the gas transport properties. However, research on methane adsorption rate characteristics and diffusion behavior in shale is not well established. In this study, high-pressure methane adsorption isotherms and methane adsorption rate data from four marine shale samples were obtained by recording the pressure changes against time at 1-s intervals for 12 pressure steps. Seven pressure steps were selected for modelling, and three pressure steps of low (~0.4 MPa), medium (~4.0 MPa), and high (~7.0 MPa) were selected for display. According to the results of study, the methane adsorption under low pressure attained equilibrium much more quickly than that under medium and high pressure, and the adsorption rate behavior varied between different pressure steps. By fitting the diffusion models to the methane adsorption rate data, the unipore diffusion model based upon unimodal pore size distribution failed to describe the methane adsorption rate, while the bidisperse diffusion model could reasonably describe most of the experimental adsorption rate data, with the exception of sample YY2-1 at high pressure steps. This phenomenon may be related to the restricted assumption on pore size distribution and linear adsorption isotherm. The diffusion parameters α and β/α obtained from the bidisperse model indicated that both macro-and micropore diffusion controlled the methane adsorption rate in shale samples, as well as the relative importance and influence of micropore diffusion and adsorption to adsorption rate and total adsorption increased with increasing pressure. This made the inflection points, or two-stage process, at higher pressure steps not as evident as at low pressure steps, and the adsorption rate curves became less steep with increasing pressure. This conclusion was also supported by the decreasing difference values with increasing pressures between macro-and micropore diffusivities obtained using the bidisperse model, which is roughly from 10 −3 to 10 0 , and 10 −3 to 10 −1 , respectively. Additionally, an evident negative correlation between macropore diffusivities and pressure lower than 3-4 MPa was observed, while the micropore diffusivities only showed a gentle decreasing trend with pressure. A mirror image relationship between the variation in the value of macropore diffusivity and adsorption isotherms was observed, indicating the negative correlation between surface coverage and gas diffusivity. The negative correlation of methane diffusivity with pressure and surface coverage may be related to the increasing degree of pore blockage and the decreasing concentration gradient of methane adsorption. Finally, due to the significant deviation between the unipore model and experimental adsorption rate data, a new estimation method based upon the bidisperse model is proposed here.

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Section: Introductionmentioning

confidence: 99%

Methane Adsorption Rate and Diffusion Characteristics in Marine Shale Samples from Yangtze Platform, South China

et al. 2017

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“…However, there have been no previous studies of shale matrix permeability over a range of effective stresses and pore pressures [14][15].…”

Section: Background Study On Stress Dependent Permeabilitymentioning

confidence: 99%

“…Expanding on the introduction above, flow in gas shale (and similarly tight rocks) is described by a combination of transport mechanisms acting at different scales [15][16]. It is common to denote transitions between these various flow regimes using the dimensionless Knudsen number, defined as:…”

Section: Flow Regime Effects On Permeabilitymentioning

confidence: 99%

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Laboratory Investigation to Assess the Impact of Pore Pressure Decline and Confining Stress on Shale Gas Reservoirs

Memon¹,

Tunio²,

Mahesar³

et al. 2018

Mehran Univ. res. j. eng. technol.

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Four core samples of outcrop type shale from Mancos, Marcellus, Eagle Ford, and Barnett shale formations were studied to evaluate the productivity performance and reservoir connectivity at elevated temperature and pressure. These laboratory experiments were conducted using hydrostatic permeability system with helium as test gas primarily to avoid potential significant effects of adsorption and/or associated swelling that might affect permeability.It was found that the permeability reduction was observed due to increasing confining stress and permeability improvement was observed related to Knudsen flow and molecular slippage related to Klinkenberg effect. Through the effective permeability of rock is improved at lower pore pressures, as 1000 psi. The effective stress with relatively high flow path was identified, as 100-200 nm, in Eagle Ford core sample. However other three samples showed low marginal flow paths in low connectivity.

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“…The matrix porosity generally is lower than 0.1, and the matrix permeability ranges from 1 nanoDarcy to 1 microDarcy (Wang et al 2009). The shale formation acts as both the source rock and the reservoir rock, so adsorbed gas and free gas coexist in shale reservoirs (Yao et al 2013a), where free gas is stored in the matrix pore space, and adsorbed gas can make up to 20 %-85 % of the total gas reserve (Hill and Nelson 2000).…”

Section: Introductionmentioning

confidence: 99%

Influence of gas transport mechanisms on the productivity of multi-stage fractured horizontal wells in shale gas reservoirs

Wang

Sun

et al. 2015

Pet. Sci.

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In order to investigate the influence on shale gas well productivity caused by gas transport in nanometersize pores, a mathematical model of multi-stage fractured horizontal wells in shale gas reservoirs is built, which considers the influence of viscous flow, Knudsen diffusion, surface diffusion, and adsorption layer thickness. A discrete-fracture model is used to simplify the fracture modeling, and a finite element method is applied to solve the model. The numerical simulation results indicate that with a decrease in the intrinsic matrix permeability, Knudsen diffusion and surface diffusion contributions to production become large and cannot be ignored. The existence of an adsorption layer on the nanopore surfaces reduces the effective pore radius and the effective porosity, resulting in low production from fractured horizontal wells. With a decrease in the pore radius, considering the adsorption layer, the production reduction rate increases. When the pore radius is less than 10 nm, because of the combined impacts of Knudsen diffusion, surface diffusion, and adsorption layers, the production of multi-stage fractured horizontal wells increases with a decrease in the pore pressure. When the pore pressure is lower than 30 MPa, the rate of production increase becomes larger with a decrease in pore pressure.

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Pore Networks and Fluid Flow in Gas Shales

Cited by 366 publications

References 5 publications

Methane Adsorption Rate and Diffusion Characteristics in Marine Shale Samples from Yangtze Platform, South China

Methane Adsorption Rate and Diffusion Characteristics in Marine Shale Samples from Yangtze Platform, South China

Laboratory Investigation to Assess the Impact of Pore Pressure Decline and Confining Stress on Shale Gas Reservoirs

Influence of gas transport mechanisms on the productivity of multi-stage fractured horizontal wells in shale gas reservoirs

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