Abstract: Longdong coalfield in the southwestern margin of Ordos Basin is rich in low-grade coalbed methane resources. The exploration, exploitation and research in this area are still in the initial stage, and the understanding of main controlling factors and models of reservoir accumulation is still insufficient. To clarify coalbed methane enrichment law and optimize the exploration target areas, the drilling(field desorption, well test and core),logging, hydrological and geochemical test data were used to discuss the coal reservoir characteristics, main controlling factors and gas rich accumulation mechanism of the gas reservoir from the aspects of tectonic evolution,buried depth, sedimentary environment and hydrogeology conditions, and four coalbed methane accumulation models and corresponding gas reservoir types were classified and three favorable exploration areas were optimized. The results show that the thickness of coal seam in Longdong area is large,the heterogeneity of coal measure strata is strong, the coalification degree of coal rock is low, and the lateral variation of gas content is fast. Coal rocks have strong hydrocarbon generation capacity and good reservoir performance, the main controlling factors of rich gas accumulation are the development degree of caprocks and the adjustment of secondary biogas in the later stage. Buried depth controlling reservoir presents the characteristics of "optimal depth". The results provide reference and guidance for the well deployment of coalbed methane exploration in the later stage.

Key words: accumulation models, coalbed methane, low-grade coal reservoir, Jurassic, Longdong coalfield