Enrichment characteristics, exploration and exploitation progress, and prospects of deep shale gas in the southern Sichuan Basin, China

Deep shale gas reservoirs are vital for the future development of China’s natural gas industry. Presently, China has achieved preliminary industrial exploitation in this regard, as evidenced by the successful drilling of several high-yielding wells, the delineation of the second gas production growing area with estimated gas-in-place of around one trillion cubic meters and gas production of around ten billion cubic meters, and innovative breakthroughs in research on shale gas enrichment pattern together with exploration and exploitation technologies. These have facilitated the large-scale, effective shale gas production growth in China. Meanwhile, the United States has achieved industrial exploitation of four major deep shale gas blocks, leading to constant rise of the shale gas production from deep reservoirs reaching 313.2×10⁹ m³ in 2021, which accounts for up to 41 % of its total natural gas production. Through systematical summary, we determine six major shale gas enrichment characteristics for deep marine reservoirs: (1) deepwater shelf deposits in a strong reducing environment, which are favorable for organic matter enrichment and preservation; (2) high-quality reservoirs with stable thicknesses and a continuous distribution in large scale; (3) prevalent ultra-high pressure with good sealing capacity of faults; (4) well-developed organic pores and fractures, resulting in favorable reservoir physical properties; (5) superior gas-bearing property of deep shales where shale gas resources are available; and (6) a high proportion of free gas in deep shales, leading to high single-well production in the initial stage. Despite these characteristics as well as advancements in the exploration and exploitation of deep shale gas reservoirs in China, three challenges are posed in the study along with corresponding countermeasures for profitable shale gas extraction from deep reservoirs. Prospects show that deep marine shale gas reservoirs in the Sichuan Basin hold discovered shale gas in place of (3～5)×10¹² m³, suggesting potential gas production growth of (30～50)×10⁹ m³. It is suggested to persist in tackling key problems, and accurately build a “transparent geological body” for shale reservoirs by adhering to the philosophy of maximizing producing reserves. Furthermore, we should focus on the optimal engineering techniques and production systems to maximize single-well estimated ultimate recovery (EUR), to continually reduce exploitation costs and consistently surpass current shale gas production limits, with the ultimate purpose of driving further progress in China’s shale gas industry.