Enrichment laws and scale effective development of shale gas in the southern Sichuan Basin

摘要

Based on the newest understandings of geological assessment and new progresses in engineering technologies in the development of shale gas rich in the southern Sichuan Basin, this paper analyzed the shale gas enrichment laws and the key factors of its commercial production, discussed the scale and efficient development modes, and clarified the further developing orientation. The following findings were concluded. (1) The Lower Silurian Longmaxi shale is the sweetest spot in this study area with a low density and a high uranium/thorium (U/Th) ratio, TOC content, quartz content, and free gas content. Besides, its distribution laws are mainly controlled by the sedimentary facies of deep water shelf. (2) The overpressured zones away from the ancient (present) erosion zones and large faults, mainly controlled by multi-stage tectonic evolution, belong to the most favorable sweet spots not only because there are well-developed organic matters and pores but the produced gas there is mainly of secondary cracking retention oil. (3) Layout, drilling, completion (fracturing) and management of wells will be essential to achieve high productions in the shale gas production. (4) The existing main technologies have helped achieve efficient development of quality shale gas resources underground less than 3500?m in such national shale gas demonstration zones as Changning–Weiyuan, Zhaotong, etc. Also, there shows a good potential of shale gas resources in those shallower strata and the strata with the burial depth of 3500–4000?m. In conclusion, with the help of continuous progress in technologies, an annual shale gas production rate of 40 billion cubic meters will be possibly achieved in this study area.