A Study On Reservoir-forming Mechanism Of Multi-layered Natural Gas In Marine Strata Of The Northwest Sichuan Basin

For a long time,a lot of researches have been made on the mechanism of gas accumulation in Northwest Sichuan,but research mainly focused on the Permian or Triassic natural gas accumulation mechanism,but the study on the mechanism of gas accumulation in the marine strata of the Sichuan basin is still very weak.It has a critical role for the northwest of Sichuan basin and the whole Sichuan basin natural gas accumulation mechanism to understand main controlling factors of the reservoirs in the northwest marine strata of natural gas accumulation process and accumulation model.Based on the above reasons,this article from the origin of natural gas source in the study area and the reservoir conditions to start,based on summing up the results of previous studies,combined with my understanding of the field geological survey and retrieve samples for laboratory analysis,application of geological theory,Northwest Sichuan marine strata of multi layer gas reservoir forming mechanism of a detailed study.To collect natural gas data,the origin and source of natural gas in the area to carry out a comprehensive study.The study of natural gas in the Northwest Sichuan is mixed filling characteristics of multi-source and multi period.Overall,the natural gas in the northwest of Sichuan are mixture accumulation with the main reservoir of oil cracked gas and pyrolysis gas of kerogen high-over mature stage.The natural gas in the northwest of Sichuan mainly originates from the two Permian and deep Cambrian source rocks,some areas have generated the Silurian hydrocarbon source rocks of natural gas as a supplement.The marine facies reservoir in Northwest Sichuan is mainly located in the Qixia formation,the Maokou formation,the Feixianguan formation,the Changxin formation and the Leikoupo formation.The reservoir conditions of the Qixia formation and the Mao Group are good,and the oil and gas shows better.The reservoir performance is mostly low porosity,low permeability fracture-pore type and pore-fracture type reservoir.We found that the accumulation of natural gas is mainly controlled by reservoir conditions and preservation conditions by analyzing of the reservoir forming factors of gas reservoirs in Jiulong Mountain gas field and Zhongba gas field.It is considered that the gas accumulation in the study area is divided into two stages by analyzing the date of the homogenization temperature of fluid inclusions at the same time as the organic inclusions.In addition,the history of tectonic evolution and thermal evolution help to study natural gas reservoir forming process.The hydrocarbon source rocks in Triassic have entered the peak.Then,the oil and gas generated by the lower Permain were gathered in the Middle Jurassic.But the formation of the smaller gas reservoir because of the limitation of the ability of gas generation.The Cretaceous is the main reservoir period.At the time,the lower Permian hydrocarbon source rocks generate a large amount of dry gas.At the same time,the underlying migration of the underlying oil is generated.The natural gas was distributed and adjusted in the Himalayan period.Finally,the formations of natural gas reserves remain so far.Based on the above research results,reservoir-forming mechanism of multi-layered natural gas in marine strata of the Northwest Sichuan Basin is summarized: Yanshan period is the main period of generation and accumulation of the high mature gas in the Northwest Sichuan Basin.Then they are adjusted to the present gas reservoirs in Himalayan period.The characteristics of this process are “Multi-stage Accumulation,Accumulation in Yanshan and Himalayan Period,Adjustment in Himalayan Period”.The reservoir forming process is characterized by multi-period.