Source-reservoir configuration and natural gas prospects of the Leikoupo Formation in Tongnan-Hechuan area, Sichuan Basin

The Middle Triassic Leikoupo Formation is one of the key strategic replacement intervals for natural gas exploration in the Sichuan Basin. To elucidate the source-reservoir configuration of the Leikoupo Formation, this study focuses on the Tongnan-Hechuan area in the southern part of central Sichuan Basin to comprehensively analyzes the source rock and reservoir data. The results reveal three sets of source rocks in the Leikoupo Formation within the study area:evaporitic lagoon source rocks in the first member (Lei 1); evaporitic to restricted lagoon source rocks in the first and second submembers of the third member (Lei 3¹-Lei 3²); and open lagoon source rocks in the third submember of the third member (Lei 3³). Among these, the Lei 3¹-Lei 3² submembers exhibit the highest hydrocarbon generation potential and constitute the main source rock interval. Four types of reservoirs are identified in the Leikoupo Formation:intragranular pore-dominated grain-shoal reservoirs in the Lei 11 submember, clay intercrystalline micropore-rich argillaceous limestone reservoirs in the Lei 3² submember, dolomite intercrystalline micropore-dominated high-quality dolostone reservoirs in the Lei 3³ submember, and a potential weathered karst reservoir at the top of the Leikoupo Formation. Vertically, three source-reservoir assemblages occur in the Leikoupo Formation:a self-sourced and self-reservoired assemblage in the Lei 11 submember; a self-sourced and self-reservoired assemblage in the Lei 3¹-Lei 3² submembers; and a lower-source/upper-reservoir assemblage comprising the Lei 3³ submember through the Lei 4 Member and the top of the Leikoupo Formation. The Leikoupo Formation thus has favorable conditions for hydrocarbon generation and reservoir development. Future exploration should focus on the hydrocarbon generation centers and consider areas with well-developed fractures and gypsum caprocks. These findings provide an important reference for strategic selection of exploration areas for natural gas in the Leikoupo Formation.