Characteristics of Pore-Fracture Development in Coal Reservoirs Constrained by Coal Facies: A Case Study of the Ningdong Coalfield
Year: 2026
Type: article
Abstract: High Resolution Image Download MS PowerPoint Slide Coal facies differentiation is a primary control on the development of pore-fracture systems in coal reservoirs. Using samples from diverse sedimentary environments of the Jurassic Yan’an Formation in the Ningdong Coalfield, this study integrates coal petrological analysis, multiscale pore characterization, and rock mechanical testing to examine the characteristics of pore-fracture development as constrained by coal facies. The results indicate that the study area developed four types of peat swamps: wetland herbaceous peat swamp (WLHPS), dry forest peat swamp (DFPS), moist forest peat swamp (MFPS), and shallow-water covered forest peat swamp (SWCFPS), with DFPS being dominant. Among primary pores, cellular pores are most developed in WLHPS (mean 12.68 μm), whereas pores in forest peat swamps (including DFPS, MFPS, and SWCFPS) are smaller. For mineral-related pores, intercrystalline pores dominate in WLHPS (mean 12.36 μm), while dissolution pores are well-developed in DFPS. Pore structure analysis reveals that forest peat swamps exhibit higher pore volumes (0.12–0.16 cm 3 /g) than WLHPS (0.06 cm 3 /g), with SWCFPS containing the highest proportion of macropores. Average specific surface area is also greater in forest peat swamps than in WLHPS. Analysis of the fracture system indicates that WLHPS has lower porosity but the smallest proportion of isolated pores. Cleat fractures are well-developed in DFPS, although partial mineral filling reduces pore connectivity. MFPS exhibits the best pore connectivity (CT-connected porosity: 16.39%). Mechanical response analysis shows that elastic modulus decreases with increasing water coverage depth, while rigid minerals such as calcite and pyrite significantly enhance deformation resistance. Coal facies are the core controlling factor of the pore-fracture system: SWCFPS, characterized by high pore volume, preferential formation of connected macropores, and moderate gelification, represents the optimal reservoir for coalbed methane (CBM) development; the high-connectivity cleat system in DFPS requires mitigation of mineral filling risks; and the low pore volume and isolated pores in WLHPS constrain its seepage capacity.
Source: ACS Omega
Institutions: Sinopec (China), Nanjing University
Language: English
Subfield: Ocean Engineering
Field: Engineering
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $1,935
OpenAlex ID: W7155016744