Comparative analysis on the enrichment patterns of deep and shallow CBM in Junggar Basin

Coalbed methane (CBM) resources are abundant in Junggar Basin and some breakthroughs have been made in CBM exploration.However, the overall exploration level is low, besides there are great differences in the enrichment laws of deep CBM and shallow CBM.In order to find out the differences and more rational use of resources, this paper studied the source characteristics, geological conditions and preservation conditions of deep CBM and shallow CBM, analyzed the occurrence characteristics and main controlling factors of deep CBM and shallow CBM, and established the reservoir-forming model of deep CBM and shallow CBM, at last, pointed out the exploration direction.The results show that the shallow CBM has the characteristics of three gas sources replenishment, the gas sources are biogas, thermogenic gas and deep migration gas.Coal pore is dominated by macro pore and transitional pore.In addition to adsorbed gas, there is a large amount of free gas in coal seam, which accounts for 36% on average.Shallow CBM are accumulated in syncline of fold structure and hydrodynamic retention area.Deep CBM has the characteristics of two gas sources replenishment.The two gases are the mogenic gas and deep migration gas.The Xishanyao Formation is dominated by free gas, accounting for more than 60% of the total, accumulated in the high part of the structure.Coal and sand of the Badaowan Formation are well developed, which are effective reservoir of natural gas, also, forming an adsorption-free symbiotic gas reservoir.It is preliminarily considered that the exploration of adsorbed gas is the first, then explored the free gas in shallow strata.While in deep strata, the exploration of free gas in the Xishanyao Formation is mainly to search for lithologic traps or structural traps.The CBM and sandstone gas are explored together in the Badaowan Formation in order to improve the utilization rate of resources.