Middle to low rank coalbed methane accumulation and reservoiring in the southern margin of Junggar Basin

The southern Junggar basin (SJB) bears huge amount of middle-low rank coalbed methane, with relatively low exploration extent, and the lack of knowledge in gas accumulation and its main controlling factors restrict the development practice. Based on the tectonic, sedimentary, hydrogeology, reservoir physical characteristics and gas content distributions, the gas accumulation and reservoiring models have been summarized. The coal-bearing strata in SJB develop in the north of Tianshan Range, with extensively developed east-west direction faults and anticlines; the coal-bearing strata were deposited in alluvial-fluvial facies, resulting in several layers of coal seams and sandstone-coal combinations; and the coal seam dip angle is as much as 50°, with the oxidation zone extends to 400-600 m. Based on the upon characteristics of “deep burried low rank coals, steep and thick coal seams, coal-sandstone combinations, fault cutting coal zones” in SJB, the model of “self-adsorption and hydraulic sealing type of steep coal seam” suiting for Fukang area in the east, “multiple coal seam pressure closed type in fault and fold belts” in the middle areas and the “structural and lithological trapped gases of multiple sources in coal bearing strata” in the deep buried areas in the west are proposed. The relatively high point of structures and gently inclined strata should be firstly considered during CBM development and also of the transition belts of ground water and underground waters. Futhur, based on multi-level fuzzy evaluation, the Sigong River to Urumqi River areas in the east bear with relatively better coalbed methane resources, reservoir characteristic and preserve conditions, where should be firstly considered for development. © 2016, Editorial Office of ACTA PETROLEI SINICA. All right reserved.