Enrichment conditions and favorable areas for exploration and development of marine shale gas in Sichuan Basin

After more than ten years of exploration and practice, a series of progress has been made in marine shale gas exploration in Sichuan Basin. During that period, focusing on Wufeng-Longmaxi formations as the most favorable pay zone, a few theories for the enrichment and high production of shale gas were proposed, the exploration and development technologies integrating geological evaluation, development optimization, optimal-fast drilling, volume fracturing, factory operation and clean exploitation was formed, and a large shale gas field with reserves of one trillion cubic meters was proved. At an important time for the development of shale gas exploration in China, it is of great significance to promote the exploration and development of marine shale gas by reviewing the exploration and development history of marine shale gas, summarizing the achievements and knowledge of shale gas in Wufeng-Longmaxi formations in terms of geological conditions and enrichment laws, and making an outlook on the key replacement fields for marine shale gas exploration in Sichuan Basin. (1) The exploration and development of marine shale gas in Sichuan Basin have gone through four stages: layer and zone evaluation stage to find the target; pilot test stage of shallow to medium-deep reservoir; demonstration zone construction stage of shallow to medium-deep reservoir; stage of shallow to medium-deep reservoir production, deep reservoir evaluation, non-pressurized shale gas evaluation, three-dimensional development evaluation, ultra-deep and new reservoir exploration. (2) The sedimentary conditions of the Wufeng-Longmaxi formations in Sichuan Basin are superior, in which the deep-water shelf shales with high organic content are continuously and stably distributed. Shale gas mainly occurs in organic matter pores, and its reservoirs are concentrated longitudinally with large continuous thickness. The structures are relatively simple in the southern Sichuan Basin and the Fuling block of southeastern Sichuan Basin. The conditions for shale gas enrichment and preservation include sustained gas supply and reservoirs far away from the ancient/present denudation areas and oil-gas escape areas in large faults. At present, the shale gas resources in Wufeng-Longmaxi formations are 3319 × 1012m3 with a proved rate of 9. 4%, showing great exploration potential. (3) There are rich marine shale gas resources in Sichuan Basin. In addition to Wufeng-Longmaxi formations, there are several sets of marine shale gas reservoirs as reserves in the horizons shallower than 4500 m. The Cambrian Qiongzhusi Formation, Permian Wujiaming Formation and Dalong Formation as the strategic breakthrough strata, the favorable shale gas reservoirs mainly lie in Weiyuan-Ziyang area inside and around aulacogen for Qiongzhusi Formation, with the predicted resource potential of 1. 40 × 1012m3, and in Jiange-Nanjiang area and Dazhu-Kaijiang area of northern Sichuan Basin, and Lichuan area of southeastern margin of Sichuan Basin for Wujiaping Formation and Dalong Formation, with the predicted resource potential of 0. 91 × 1012 m3. The Member 1 of Xujiahe Formation as the strategic preparation layer, its favorable shale gas reservoirs mainly lie in Ya'an-Qionglai area, with the predicted resource potential of 0. 88 × 1012 m3 © 2023 Science Press. All rights reserved.