An anisotropic pore-network model to estimate the shale gas permeability

Di Zhang,Liming Hu,Haohao Guo,Jay N Meegoda,Dantong Lin,Xinghao Zhang

doi:10.1038/s41598-021-86829-4

Di Zhang, Liming Hu + Show 4 more

Open Access

https://doi.org/10.1038/s41598-021-86829-4

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Abstract

The permeability of shale is a significant and important design parameter for shale gas extraction. The shale gas permeability is usually obtained based on Darcy flow using standard laboratory permeability tests done on core samples, that do not account for different transport mechanisms at high pressures and anisotropic effects in shales due to nano-scale pore structure. In this study, the permeability of shale is predicted using a pore network model. The characteristics of pore structure can be described by specific parameters, including porosity, pore body and pore throat sizes and distributions and coordination numbers. The anisotropy was incorporated into the model using a coordination number ratio, and an algorithm that was developed for connections of pores in the shale formation. By predicting hydraulic connectivity and comparing it with several high-pressure permeability tests, the proposed three-dimensional pore network model was verified. Results show that the prediction from the anisotropic pore network model is closer to the test results than that based on the isotropic pore network model. The predicted permeability values from numerical simulation using anisotropic pore network model for four shales from Qaidam Basin, China are quite similar to those measured from laboratory tests. This study confirmed that the developed anisotropic three-dimensional pore network model could reasonably represent the natural gas flow in the actual shale formation so that it can be used as a prediction tool.

Highlights

This study confirmed that the developed anisotropic three-dimensional pore network model could reasonably represent the natural gas flow in the actual shale formation so that it can be used as a prediction tool
As for the anisotropic pore network used in this research, the reasonable anisotropic ratio has to be adopted based on the previous research and the relationship between the anisotropic ratio, which refers to the connection number ratio in each plane as
At nano/micro-scale flow simulations, the approach proposed by Song et al.[11] with pore structure obtained by scanning-electron-microscopy (FIB-SEM) and using the local-effective-viscosity multi-relaxation-time lattice Boltzmann model to simulate the gas transport in shale would be preferable

Summary

Introduction

This study confirmed that the developed anisotropic three-dimensional pore network model could reasonably represent the natural gas flow in the actual shale formation so that it can be used as a prediction tool. This equivalent pore network can represent the average actual pore structure of shale so that the anisotropic permeability can be simulated.

Results

Conclusion