Exploration prospects of Lower Cambrian shale gas in the central-western Sichuan Basin under the pattern of tectonic-depositional differentiation: From high-quality source rocks to reservoirs

The Lower Cambrian Maidiping-Qiongzhusi Formation is another major layer of shale gas exploration and development strata after the Upper Ordovician Wufeng Formation and Lower Silurian Longmaxi Formation in the Sichuan Basin. However, the stratigraphic division and correlation of the Lower Cambrian in the central-western Sichuan Basin is still disputed, which restricts the research and evaluation on the Lower Cambrian shale gas. To this end, this paper systematically analyzes the stratigraphic and time frame of Lower Cambrian (as conventional oil and gas source rocks) in the central-western Sichuan Basin and the formation and distribution laws of black shale. Then, combined with its structural setting of great burial depth, strong uplifting and strong reworking, the thermal evolution process of Lower Cambrian shale organic and the enrichment conditions of shale gas are studied. Finally, the favorable areas are pointed out. And the following research results were obtained. First, referring to the international Cambrian stratigraphic and time correlation sequence, the time-spatial distribution relationship of the Lower Cambrian black rock series in this area is controlled by the difference of Sinian-Cambrian contact, and the Maidiping-Qiongzhusi Formation is not completely pure black rock series. Second, in the pattern of tectonic-depositional differentiation, the thickness of the Maidiping-Qiongzhusi Formation in the central-western Sichuan Basin varies greatly and the middle-northern section of the Mianyang-Changning Intracratonic Sag is the depositional center of organic-rich black shale, as well as the optimal shale gas enrichment area. Third, there is a local moderate-maturity area of Maidiping-Qiongzhusi Formation in the Sichuan Basin. In conclusion, on the basis of effective fracturing technical problems for 4 000 m deep engineering, the Ziyang-Neijiang-Dazu on the east of Weiyuan structure in the Sichuan Basin is the most favorable exploration area, and the Kuangshanliang-Nianziba-Hewanchang area in the foreland expanded deformation zone of northern section of western Sichuan Depression and the Micang Mountain front area can be taken as the favorable exploration shale gas areas in the next step. © 2021, Natural Gas Industry Journal Agency. All right reserved.