Geological Controls on CBM Enrichment and its Exploration Target Optimization in the Southeast Junggar Basin, China

Abstract

To date, coalbed methane (CBM) explorationhas only achieved a big breakthrough in Fukang-Dahuangshan regions, while CBM exploratory wells in the other regions of the southeast Junggar basin exhibit poor exploration effects. The analysis suggests that three unclear factors, including CBM accumulation process, geological controlling factors and distribution principle of favourable areas, cause the mismatch between CBM exploratory well deployment and practical geological regularity. In this study, the systematic research about three unclear factors has been carried out for the first time. The research shows that the well-developed extruding thrust faults are beneficial to CBM enrichment and preservation in the study area. Sandy roof not only can form tight-sandstone gas reservoir, but also serve as the cap rock for underlying coalbed gases. Liuhuanggou-Fukang regions in the southern Junggar basin and depression regions in the eastern Junggar basin are all hydrodynamic stagnation areas beneficial to CBM enrichment. Seven typical CBM enrichment models are summarized in this study, and they have different development degrees and various controlling mechanism of CBM enrichment. Finally, a suitable mathematical evaluation model for CBM exploration potential is established, and seven prospective targets (e.g. Fukan, Liuhuanggou and Qigu areas, etc.) are selected to be the preferred areas for CBM exploration, and both of them are ordered on the basis of their Ui values. The findings provide the geological basis for future CBM exploration and deployment.