Accumulation characteristics and exploration prospects of the 4th member of Leikoupo Formation in the western Sichuan Basin, China

Abstract

The Leikoupo Formation of the Middle Triassic is one of the hot strata of marine natural gas exploration in the western Sichuan Basin in recent years. Petroleum geologists have different opinions on the reservoir-forming conditions and the types of gas pools. The research shows that the 4th member of Leikoupo Formation in the western Sichuan Basin has favorable hydrocarbon accumulation conditions. It not only has a large-scale stable distribution of the tidal flat dolomite reservoirs, but also develops two sets of source rocks: the Permian source rock and the Leikoupo Formation source rock. There are three models of hydrocarbon accumulation in the 4th member of Leikoupo Formation from the east to the west in the Western Sichuan Depression. That is the “lower generation and upper storage” structural gas reservoir transported by cross-layer source faults and fractures, the “lower generation and upper storage” structure-formation gas reservoirs transported by the relay combination of small source faults and intra-layer fractures, and the “self-generating and self-accumulation” lithologic gas reservoir transported by intra-layer fractures. After the proved reserves of 100 × 10⁹ m³ of the structural gas reservoir in the 4th member of Leikoupo Formation in the western Sichuan Basin, it is considered that the area near the pinch-out line of the 4th member of Leikoupo Formation in the eastern depression is a favorable area for exploration of tectonic-stratigraphical gas reservoirs, and the middle and lower part of the eastern slope (Guanghan slope) in the Western Sichuan Depression is a favorable area to explore lithologic gas reservoirs.