Abstract
The gas flow mechanisms in source rocks of coal measures under the effects of the pore structures and permeability characteristics were investigated by field-emission scanning electron microscopy, low-pressure nitrogen gas adsorption, high-pressure mercury intrusion, and pressure pulse decay permeability method. Various flow regimes were distinguished in the pores and fractures of differing scales, and the mass fluxes through the same were calculated using the data obtained by the numerical and experimental investigations. Results indicated that mesopores predominated in shale, while coal contained well-developed mesopores and macropores. In addition, the permeabilities of coal and shale were observed to be significantly anisotropic and highly stress dependent. The cross-sectional area proportions of the pores per unit cross-sectional area of the matrix in the free molecular, transition, and slip flow regimes in shale and coal were determined to be, respectively, 0.2:0.7:0.1 and 0.15:0.6:0.25. In the free molecular and transition flow regimes, the mass flux decreased with increasing reservoir depth, while the reverse was the case in the slip flow regime. Further, in the continuum flow regime, the mass flux was unimodally distributed with respect to the reservoir depth. The total mass flux in coal was greater in the direction perpendicular to the bedding compared to the direction parallel to the bedding, while the reverse was the case in shale. In addition, the continuum flow regime predominated in coal in both the directions perpendicular and parallel to the bedding, but only in the direction parallel to the bedding in shale. This work presents a comprehensive model for the analysis of all the flow regimes in pores and fractures of differing scales, as well as the anisotropy. Findings of the study are meaningful for establishing the coupling accumulation mechanism of the Three Coal Gases and developing a unified exploration and exploitation program.
Highlights
The unconventional gas resources in coal measures mainly comprise coalbed methane (CBM), shale gas, and tight sandstone gas, commonly referred to as the ‘‘Three Coal Gases’’ (Cao et al, 2014; Hou et al, 2016)
The unified exploration and exploitation of the Three Coal Gases has been a major research subject because it is considered to be an effective means of improving the production of unconventional gas resources contained in coal measures (Qin et al, 2016; Zhu et al, 2016)
This paper presents a gas flow model that comprehensively considers the various flow regimes in pores/fractures of differing scales under the effects of the pore structures and permeability characteristics
Summary
The unconventional gas resources in coal measures mainly comprise coalbed methane (CBM), shale gas, and tight sandstone gas, commonly referred to as the ‘‘Three Coal Gases’’ (Cao et al, 2014; Hou et al, 2016). This paper presents a gas flow model that comprehensively considers the various flow regimes in pores/fractures of differing scales under the effects of the pore structures and permeability characteristics. This is aimed at establishing the coupling accumulation mechanism of the Three Coal Gases. The high-pressure mercury intrusion (HPMI) experiment was performed in the Key Laboratory of Coalbed Methane Resources and Reservoir Formation Process, Ministry of Education, China University of Mining and Technology. The pressure pulse decay permeability experiment was performed at the Key Laboratory of Coalbed Methane Resources and Reservoir Formation Process, Ministry of Education, China University of Mining and Technology. The analysis of the experimental results was basically based on Darcy’s law
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
