Study on Characteristics of Favorable Reservoirs for High-Rank Coals, North China

Abstract

The Late Paleozoic coalbed methane (CBM) reservoirs for high-rank coal in North China have the characteristic of high CBM content. But due to the differences between CBM reservoirs in several aspects such as physical property and gas accumulation condition, CBM was developed for commercialization only in the south of Qinshui Basin. Coal samples were systematically collected from Qinshui Basin, Jiaozuo Coalfield, Yongxia Coalfield and Xinggong Coalfield, and then tested on coal petrology, porosity-permeability characteristics and isothermal adsorption, etc. Based on the analyses of these test data, this paper discusses the forming conditions and mechanisms of the favorable CBM reservoirs for high-rank coals. These factors like the coal petrology characteristics, reservoir physical property and gas accumulation conditions were detailedly discussed. The difference characteristics of the favorable CBM reservoirs in North China were comprehensively evaluated as conclusions. The result shows that in comparison with other high-rank coal areas, coals in Qinshui Basin have undergone slight tectonic destruction, which induces the widespread development of primary- and cataclastic-structured coals, developing better microfractures. Moreover, the Qinshui coals have not only the well-developed exogenetic fractures, but also well sedimentary and tectonic conditions at the key accumulation period of CBM. These factors resulted in the formatting of better CBM reservoir in Qinshui Basin when comparing to other high coal rank areas in North China.