Characteristics of CBM reservoirs and exploration potential in Jiergalangtu sag of Erlian basin

The coal seams distribution, petrographic characteristics and coal qualities, pore characteristics, and isothermal adsorption features of coal seams in Jiergalangtu sag of Erlian basin were analyzed. The exploration potential of CBM was predicted from the aspects of CBM generation and preservation conditions. It was considered that the coal seams in this sag are at a stage of low-rank of lignite with a thickness of 10~394 m and coal macerals are dominated by huminite with a volume fraction of 80.5%~96.7%. Langmuir volumes are high, ranging of 3.55~10.88 m³/t with a average of 7.29 m³/t. Pore structures are dominated by micropores and small pores, with the open cylindrical pore or parallel-plate pore morphologies, which provides a favorable condition for CBM desorption. Then the gas content of the coal seams in this area was tested to be from 0.97 to 3.83 m³/t with a average of 2.08 m³/t. The exploration potential of the sag is comprehensively evaluated and the target areas of CBM exploration in the future are the southeast of the sag. There are three advantages. ①Coal seams are away from normal faults and CBM is not easy to escape. ②The roof lithologies of coal seams are mainly mudstone and silty mudstone, which are beneficial to the preservation of CBM. ③There is the supply of secondary biogenic gas.