Abstract: The Qitaihe fault depression in the Boli basin is rich in coalbed methane resources, but the exploration level is low, and the understanding of the enrichment and accumulation laws and mechanisms is insufficient, which restricts exploration practice. Based on a detailed dissection of the geological conditions of coalbed methane in the Qitaihe fault depression, this article reveals the enrichment characteristics and reservoir formation mechanism of coalbed methane in the study area. The study found that the coalbed methane reservoir in the Qitaihe fault depression has good conditions, with many coal seams in the Lower Cretaceous Chengzihe Formation, a large total thickness of coal seams, multiple developed coal rich centers, and a high degree of thermal evolution. The physical properties of coal reservoirs are favorable, and the gas content of coal seams is generally characterized by high in the west and low in the east. The structure, the hydrology,  the sealing and other preservation conditions benefit coalbed methane reservoir formation. There are three types of models of coalbed methane reservoir formation, syncline-hydraulic sealing, fault sealing-hydraulic sealing, and fault-multi seam self-sealing. Under moderate burial depth and slow stagnant water environment, the reverse fault sealing area, secondary structural high point, and middle coal seam stratification are favorable locations for coalbed methane enrichment. On this basis, a multi-level fuzzy mathematics evaluation model for coalbed methane selection was established, and favorable areas were evaluated. Seven coalbed methane favorable areas were selected, including Qinglongshan-Taoshan district and Machang district.

Key words: Boli basin, Qitaihe fault depression, coalbed methane, enrichment characteristics, reservoir forming mechanism, reservoir forming mode, multi-level fuzzy mathematics, favorable area optimization