Enrichment patterns and exploration countermeasures of deep coalbed methane in the Linxing-Shenfu block on the eastern margin of the Ordos Basin

[Objective] Some insights have been gained into the enrichment and accumulation patterns of deep coalbed methane (CBM) in high-rank coal seams on the eastern margin of the Ordos Basin, represented by the Daning-Jixian block. However, the exploration of deep CBM in medium-rank coal seams in the Linxing-Shenfu block, located in the northern segment of the basin's eastern margin remains in its initial stage, leading to an inaccurate and unclear understanding of the enrichment and accumulation patterns. This necessitates summarizing these patterns to effectively guide deep CBM exploration and exploitation. [Methods] Focusing on the Nos.8 and 9 coal seams of the Taiyuan Formation in the Linxing-Shenfu block, this study investigated the factors controlling source rock - reservoir configuration, along with hydrocarbon generation, occurrence, and accumulation, and the coupling relationships between these factors based on the dual attributes of coals as both source rocks and reservoirs. [Results and Conclusions] Key findings are as follows: (1) The study area exhibits an east-west zoning, consisting of the eastern fault terrace zone and the western gentle zone, with the main body manifesting burial depths exceeding 1 500 m. The Nos.8 and 9 coal seams of the Taiyuan Formation are considerably thick, contain micropores and macropores, and feature moderate maturity and a high gas content in general, suggesting superior accumulation conditions for deep CBM and great potential for resource exploration. (2) The coal seams formed under sedimentary microfacies of mudflats and interdistributary bays display substantial thicknesses, high vitrinite content, and simple structures. With an increase in maturity, these coal seams exhibit increasing gas content, specifically the methane content. The critical adsorption zone of the Nos.8 and 9 coal seams, under the coupled control of temperature-pressure conditions, shows a burial depth of around 1 750 m. CBM enrichment is ensured by the high sealing performance of mudstones, stable tectonic environments, and closed hydrodynamic conditions. (3) Given the differences in geologic conditions of the study area, specific recommendations are proposed in this study. For the western gentle zone, it is necessary to accelerate the exploration of the CBM enrichment zone, expand the exploration around the area with proven reserves, and strengthen research on the compressibility of deep coal seams in the zone, with the purpose of driving large-scale production capacity construction. For the eastern fault terrace zone, it is advisable to conduct a pilot production assessment in the CBM enrichment zone and enhance the research on the transpressive-transtensional transition zone of the Lishi strike-slip fault zone, aiming to reveal new reserves. This study, systematically summarizing the enrichment and accumulation patterns of deep CBM in medium-rank coal seams of the Linxing-Shenfu block, has guided the selection of the optimal CBM accumulation zone, holding positive significance for the efficient exploration and large-scale exploitation of this block. © 2024 Science Press. All rights reserved.