Reservoir evaluation of the Lower Silurian Longmaxi Formation shale gas in the southern Sichuan Basin of China

摘要

The Lower Silurian Longmaxi Formation (the Palaeozoic) is organic-rich (black) shale in the southern Sichuan Basin (the Yangtze Plate) of China. This study analyses the lateral extent and thickness, burial depth, total organic carbon content and thermal maturity of the Longmaxi Formation black shale as the key features of the shale gas reservoir. The thickness of the black shale ranges from 10 to 170 m. The thickest reservoir is located in Changning-Naxi-Yongchuan region. The TOC of the shale at the bottom of the formation (50-m thickness) is above 2.0%. The lateral distribution of TOC varies with the lateral distribution of thickness, with the maximum TOC in the Gongxian-Luzhou-Yongchuan region. The burial depth ranges from 2000 to 4500 m. The shale is thermally over mature. The evaluation of reservoir characteristics indicates that the Longmaxi Formation has conditions appropriate for shale gas accumulation and thus resource potential in the southern Sichuan Basin of China. The objective of this preliminary evaluation of the reservoir characteristics is to locate potential areas favourable for exploration. The most favourable areas are defined here as those where the thickness of black shale is more than 100 m and the burial depth is less than 3000 m; these cover approximately 12,600 km~2. The most favourable areas, which cover an area of approximately 5100 km~2, are located in the northeast Luzhou region.