Bitumen formation of Cambrian Longwangmiao Formation in the central Sichuan and its implication for hydrocarbon accumulation

Abstract

Based on organic petrology, organic geochemistry and SEM method, type, formation period and source of bitumens in the Cambrian Longwangmiao Formation in the central Sichuan Basin were well investigated, and combined with fluid inclusions and tectonic evolution characteristics, the hydrocarbon accumulation history of the gas reservoir of the Longwangmiao Formation in the Anyue gasfield was also studied. The result shows that all bitumens in the Longwangmiao Formation was from the Lower Cambrian source rocks, it had multiple genetic types which was dominated by the pyrolysis genetic type; the bitumens were formed into three stages, i.e., the bitumen of the oxidized water-washing type in the first stage, the bitumen of the precipitated type in the second stage, and the bitumen of the pyrolyzed type in the third stage; the gas reservoir in the Anyue gasfield experienced five stages of hydrocarbon charging, including two stages of liquid hydrocarbon charging, charging of the kerogen pyrolysis gas in the Late Triassic-Early Jurassic, charging of the crude oil pyrolysis gas in the Late Jurassic-Early Cretaceous and charging of the dry gas charging in the Himalayan trap reformation and adjustment process.