Abstract: A shallow–medium coalbed methane (CBM) field has been established in the southern Qinshui Basin with an annual production capacity of 2.6×10⁸ m³. However, the exploration of deep CBM is at a low level, and there is insufficient geological understanding. By using drilling, lab test, and trial production data of exploration wells in the study area, accumulation characteristics of deep CBM have been analyzed from four aspects, i.e., coal reservoir characteristics, thermal evolution and gas-bearing property, preservation conditions, and temperaturepressure characteristics. The study results show that: (1) The No.3 coal seam is consistent, with a total thickness of 4.0-7.3 m, which has the favorable conditions of high vitrinite content, low ash content, and well-developed fissures; (2) R_o of the No.3 coal ranges in 2.41%–3.03%, showing a high-rank coal, which has strong adsorption capacity, with an adsorbed gas content of higher than 20 m³/t; (3) The salinity of the produced water from No.3 coal is greater than 4000 mg/L, showing a NaHCO₃ water type, and it is in a weak radial flow environment. The deep CBM reservoir has the characteristics of slightly low temperature and low pressure, indicating that it has suffered certain damage, which insignificantly affected the adsorbed gas, but was not conducive to the accumulation of free gas. The conclusion suggests that the accumulation conditions for deep CBM in the study area were more favorable than the shallow–medium CBM that has already been appraised and developed in the slope zone. The estimated CBM resources of the deep No.3 coal are 1200×10⁸ m³, indicating good potential for CBM exploration and development.

Key words: southern Qinshui Basin, deep coalbed methane (CBM), accumulation characteristics, accumulation pattern, resource potential