Gas invasion is the key process of Sinian-Cambrian gas accumulation in Sichuan Basin.

Previous studies divided the Sinian-Cambrian gas accumulation processes into three stages, including (1) paleo-oil accumulation; (2) paleo-oil cracking; and (3) gas reservoir adjustment and finalization. The author thinks that they ignored a key process, during which the natural gas invades and changes the paleo-oil reservoirs into paleo-gas reservoirs. According to the micro-observation of bitumen in reservoirs, there were great differences between the asphaltene formed by gas invasion and the pyrobitumen formed by paleo-oil cracking. When the gas invasion happened in paleo-reservoirs, asphaltene was separated out and the liquid hydrocarbon was partially changed into solid bitumen which lead to the increase of gas storage for oil-cracking gas and source rocks pyrolysis gas. [ABSTRACT FROM AUTHOR]