Characteristics and favorable area evaluation of deep coalbed methane accumulation in Fugu area of the Ordos Basin

The Shenfu block on the eastern edge of the Ordos Basin is a typical deep coalbed gas field with abundant resources and enormous exploration and development potential. In October 2023, the Shenfu deep coal seam atmospheric field has successfully applied for a proven geological reserve of over 110 billion m³. The Fugu area is located in the central part of the Shenfu block and is the earliest experimental area for deep coalbed methane production. However, the understanding of its coalbed methane enrichment and accumulation patterns and exploration and development potential is still unclear. Comprehensive application of seismic, logging, drilling, and coal rock testing data to identify the geological characteristics, enrichment and accumulation patterns, and distribution of favorable areas of deep coalbed methane in the region. The results show that the main coal seams 4+5 and 8+9 have stable development and large thickness (4+5 coal:3.2-5.8 m; 8+9 coal:8.7-13.5 m), and favorable layers are mainly distributed in the middle and upper parts of the coal seam; The macroscopic coal rock type is mainly bright semi bright coal, and the coal body structure is mainly primary fragmented coal; Due to the influence of deep metamorphism, coal is mainly composed of gas coal, fat coal, and coking coal. The degree of coal metamorphism is at the peak of pyrolysis gas generation, and coal reservoirs exhibit medium to high gas content (4+5 coal:3.0~12.0 m³/t; 8+9 coal:7.5~18.5 m³/t) and gas saturation (35.0%~115%); The main coal seam belongs to a low-permeability reservoir (0.01~0.09) ×10^-3 μm²), the pore structure is mainly composed of micropores and small pores. It is proposed that the coalbed methane in the Fugu area is enriched and accumulated in a "fold fault hydrodynamic" model, with the coalbed methane enrichment area located in the tectonic gentle zone and slope zone. Establish a dual sweet spot evaluation system for deep coalbed methane geology and engineering, and identify Class I geological engineering sweet spot areas located in the east and southwest, which are the preferred areas for deep coalbed methane exploration and development in the study area. Therefore, this research further enriches the theory of deep coalbed methane enrichment and accumulation, and has important guiding significance for the exploration and development practice of deep coalbed methane in the eastern edge of the Ordos Basin.