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Gas is adsorbed in the pores of coal matrix and during gas production gas is desorbed from the pore surface and diffuses through the matrix pore structure and flows in the fracture/cleat system to the production well or boreholes. However, coal is highly heterogeneous and anisotropic. How heterogeneity and anisotropy affect the gas storage and especially the diffusion behaviour is not well studied...
The goal of this study is to investigate how coal matrix strains affect the evolution of coal permeability. In previous studies, this impact was quantified through splitting the matrix strain into two parts: one contributes to the internal swelling while the other to the global strain. It was assumed that the difference between the internal swelling strain and the swelling strain of matrix determines...
We investigated the anisotropic permeability in three directions of three cubic shale samples from Lower Silurian Longmaxi Formation in southeastern Sichuan Basin, China. The relationship between anisotropic permeability and fracture structure as characterised by micro-computed tomography (CT) and scanning electron microscope (SEM) Maps was also investigated. At confining pressure of 3MPa, permeability...
This paper presents the results of a laboratory program of work to measure the coal properties required to apply models for the behaviour of the absolute reservoir permeability during gas production. These measurements were made on core samples from the Bowen Basin of Australia, an important area for coal seam methane production, and involved applying an integrated testing methodology. During the...
Although permeability data for different gas shales have been reported previously and attempts have been made to match permeability with empirical correlations, theoretical studies of shale permeability modelling are lacking. In this work, the correlation between fracture permeability and effective stress is established for gas shales through theoretical derivation. This model is able to match the...
The coal and coalbed methane (CBM) resources are abundant in western Guizhou and eastern Yunnan, South China. However, commercial CBM production in this region has not been achieved. Reservoir properties are the prerequisites in determining the possibility of CBM exploration and its development potential. Thus, to help to select the most favorable block and to prioritize CBM development in the study...
When natural gas is extracted from coal seams, complex interactions of stress and sorptive chemistry have a strong influence on the properties of coal. These include influences on gas sorption and flow, coal deformation, porosity change and permeability modification. In this study, we define this chain of reactions as “coupled processes” implying that one physical process affects the initiation and...
This paper examines the feasibility of combining a process known as enhanced methane recovery with partial coal pyrolysis to improve the petrophysics of coal seams and ultimately extract higher methane yields with accompanying pyrolysis gases. Partial pyrolysis for coal gas generation changes the pore and fracture structure, which in turn affect the permeability. A series of laboratory experiments...
Understanding gas storage and transport mechanisms in shale is crucial for reservoir evaluation and gas production forecast. The shale matrix has a complex pore structure, with sizes ranging from nanometres to micrometres. Although diffusion plays a significant role in shale gas transport in the reservoir, systematic studies of gas diffusion in shale are rare. This paper studied the methane diffusion...
Nuclear magnetic resonance (NMR) experiments of stress sensitivity on the pore and fracture systems of coal samples with different ranks were performed. Pore compressibility was calculated based on the NMR results. The relationship between pore compressibility and effective stress was discussed and a mathematical model for pore compressibility was developed to describe the experimental data. The experimental...
For the past decades the nuclear magnetic resonance (NMR) technology has gained acceptance as a petrophysical tool for evaluating reservoir properties. Comprehensive reservoir evaluation requires determination of irreducible fluids, movable fluids and permeability. Although the NMR petrophysical properties of coals have been studied for decades, the impact of heat on these properties (pore size distribution,...
Adsorption-pore (pore size less than 100nm) and seepage-pore (pore size greater than 100nm) structures have great effects on gas adsorption/diffusion and gas flow in coal seam, respectively. Pore properties, including porosity, size/volume distribution, volumes, surface fractals, specific surface area, and connectivity, for four coals from Northeast China were acquired through mercury porosimetry,...
Gas production from coal is a complex process whereby gas, initially adsorbed in the coal matrix, desorbs and diffuses through the matrix into the cleat and eventually flows through the cleat system into a production well or a drainage borehole. Hence, the gas production rate is mainly controlled by the gas diffusivity in the matrix and gas permeability in the cleat system. Moisture in the coal matrix...
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