Pore-Scale Simulation and Sensitivity Analysis of Apparent Gas Permeability in Shale Matrix

Pengwei Zhang,Liming Hu,Jay Meegoda

doi:10.3390/ma10020104

Pengwei Zhang, Liming Hu + Show 1 more

Open Access

https://doi.org/10.3390/ma10020104

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Journal: Materials	Publication Date: Jan 25, 2017
Citations: 26	License type: CC BY 4.0

Affiliation: Tsinghua University, New Jersey Institute of Technology

Abstract

Extremely low permeability due to nano-scale pores is a distinctive feature of gas transport in a shale matrix. The permeability of shale depends on pore pressure, porosity, pore throat size and gas type. The pore network model is a practical way to explain the macro flow behavior of porous media from a microscopic point of view. In this research, gas flow in a shale matrix is simulated using a previously developed three-dimensional pore network model that includes typical bimodal pore size distribution, anisotropy and low connectivity of the pore structure in shale. The apparent gas permeability of shale matrix was calculated under different reservoir pressures corresponding to different gas exploitation stages. Results indicate that gas permeability is strongly related to reservoir gas pressure, and hence the apparent permeability is not a unique value during the shale gas exploitation, and simulations suggested that a constant permeability for continuum-scale simulation is not accurate. Hence, the reservoir pressures of different shale gas exploitations should be considered. In addition, a sensitivity analysis was also performed to determine the contributions to apparent permeability of a shale matrix from petro-physical properties of shale such as pore throat size and porosity. Finally, the impact of connectivity of nano-scale pores on shale gas flux was analyzed. These results would provide an insight into understanding nano/micro scale flows of shale gas in the shale matrix.

Highlights

The shale pore structure is of great interest in studying gas flows and shale gas extractions
Mehmani et al [8,9] developed a multi-scale pore network model to simulate hydrocarbon flow in a shale matrix, which contains both the intra-particle pores in grains and inter-particle pores between grains
Pore space connectivity is determined by the coordination number, which is a generalized mathematical parameter describing how well the pore spaces are inter-connected in porous media

Summary

Introduction

The shale pore structure is of great interest in studying gas flows and shale gas extractions. In order to quantify pore structure and its relation to mineralogical grains, pores are classified into three types, i.e., inter-particle pores, intra-particle pores, and intra-particle pores in organic matter [7] Based on this classification, Mehmani et al [8,9] developed a multi-scale pore network model to simulate hydrocarbon flow in a shale matrix, which contains both the intra-particle pores in grains and inter-particle pores between grains. Mehmani et al [8,9] developed a multi-scale pore network model to simulate hydrocarbon flow in a shale matrix, which contains both the intra-particle pores in grains and inter-particle pores between grains Another special feature of pore structure in a shale matrix is the connectivity of pore spaces. Pore connectivity is relatively low [14], and many isolated pores can be observed from

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