GEOLOGICAL CONDITIONS FOR SHALE GAS ENRICHMENT IN THE UPPER PERMIAN DALONG FORMATION, THE NORTHEASTERN CHONGQING AREA, CHINA

摘要

Significant progress has been made during the exploration of shale gas in the Lower Paleozoic Wufeng-Longmaxi Formations and the Shuijingtuo Formation in the Northeastern Chongqing Area. However, less attention has been paid to the Upper Paleozoic Dalong Formation shale, in terms of its shale gas enrichment conditions. Accordingly, this study aims to characterize the Dalong Formation shale from perspectives of its distribution, organic chemistry, reservoir capacity and gas content through combination of field measurement, experimental tests and well gas content quantification. It is demonstrated that the Dalong Formation shale is featured by dominance of Type II organic matter, moderate thickness, high TOC content, high maturity, and large gas content, all of which favor the shale gas generation and accumulation. Moreover, the presence of brittle minerals such as quartz and feldspar provide possibilities for later hydraulic fracturing, while organic pores and micro-fractures act as important reservoir space for shale gas enrichment. Compared with the other shale successions that have been producing commercial shale gas flows, the Dalong Formation shale in the Northeastern Chongqing Area has good shale gas enrichment conditions, and is thus of great shale gas exploration potentials. More attention should be paid to it in the future exploration of unconventional gas in this area.