Petrophysics characteristics of coalbed methane reservoir: A comprehensive review
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REVIEW ARTICLE
Petrophysics characteristics of coalbed methane reservoir: A comprehensive review Qifeng JIA1,2, Dameng LIU (✉)1,2, Yidong CAI1,2, Xianglong FANG1,2, Lijing LI1,2 1 School of Energy Resources, China University of Geosciences, Beijing 100083, China 2 Coal Reservoir Laboratory of National Engineering Research Center of CBM Development & Utilization, China University of Geosciences, Beijing 100083, China
© Higher Education Press 2020
Abstract Petrophysics of coals directly affects the development of coalbed methane (CBM). Based on the analysis of the representative academic works at home and abroad, the recent progress on petrophysics characteristics was reviewed from the aspects of the scale-span porefracture structure, permeability, reservoir heterogeneity, and its controlling factors. The results showed that the characterization of pore-fracture has gone through three stages: qualitative and semiquantitative evaluation of porefracture by various techniques, quantitatively refined characterization of pore-fracture by integrating multiple methods including nuclear magnetic resonance analysis, liquid nitrogen, and mercury intrusion, and advanced quantitative characterization methods of pore-fracture by high-precision experimental instruments (focused-ion beam-scanning electron microscopy, small-angle neutron scattering and computed tomography scanner) and testing methods (m-CT scanning and X-ray diffraction). The effects of acoustic field can promote the diffusion of CBM and generally increase the permeability of coal reservoirs by more than 10%. For the controlling factors of reservoir petrophysics, tectonic stress is the most crucial factor in determining permeability, while the heterogeneity of CBM reservoirs increases with the enhancement of the tectonic deformation and stress field. The study on lithology heterogeneity of deep and high-dip coal measures, the spatial storage-seepage characteristics with deep CBM reservoirs, and the optimizing production between coal measures should be the leading research directions. Keywords petrophysics, pore-fracture, permeability, heterogeneity, controlling factors
Received June 30, 2020; accepted August 31, 2020 E-mail: [email protected]
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Introduction
Coal petrology is the theoretical basis of coalbed methane (CBM) exploration and development, transformation and stimulation, and sustainable development of the industry (Jiang et al., 2016). As the source rock and storage carrier of hydrocarbon gas, the coal reservoir contains special properties such as multiscale pores and fractures, large specific surface area, and conductive medium capacity, which enable CBM to be produced effectively (Fan et al., 2010; Akhondzadeh et al., 2020). The petrological characteristics of CBM reservoirs are mainly reflected in the aspects of pore-fracture, permeability, reservoir heterogeneity, genesis mechanism, and mechanical properties (Ahmad et al., 2019; Cai et al., 2019). Many international scholars have studied the petrophysics characteristics of CBM reservoirs, mainly in t
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