On The Dynamic System Of Oil & Gas Migration And Accumulation In Baiyinchagan Depression

Located at the west edge of Erlian basin, the main strata in Baiyinchagan Depression are Cretaceous. Based on the theory of"Dynamic system for oil and gas Migration and Accumulation"and the research of structural and sedimental background, this paper divides the whole depression into five dynamic systems for pool forming upwardly, I. high pressure self sourced and half closed system in the base, II. high pressure self sourced and half closed system in the lower part, III. high pressure mixed sourced and half closed system in the middle,â…£. high to normal pressure mixed sourced and half closed system in the upper part andâ…¤. normal pressure foreign sourced and half closed to open system on the top. It also analyses the conditions and controlling factors for the oil and gas migration and accumulation system through comprehensive studies of petroleum geology, and the analysis of the characters of abnormal fluid pressure.According to the organic carbon content, kerogen type and maturity, three source rocks have been identified: Duhongmu I(K1bd1), Tenggeer Formation(K1bt) and Aershan II(K1ba2). The source rock of Duhongmu Formation I is characterized by high organic carbon content and low maturity. While the source rocks of the other two formations are characterized by relatively low organic carbon content and high maturity.According to oil show distribution, analysis of thermal history and burial history, three reservoir forming stages have been identified: first member of Duhongmu Formation, Tengar Formation and second member of Alshan Formation. The first one contains high organic but low matured hydrocarbons, while the last two consist of low organic but highly matured hydrocarbons. Further analysis suggests that these three stages correspond to the sedimentation stages of Du I member, Du III member and Saihantala Formation, which are the main oil pool formation periods.It is discovered in the study that the multistage tectonic movements favours the oil pool formation system, while the faulting and the formation of conformity lead to the construction of the system for oil and gas migration and accumulation.Based on the above study, the plays and traps in Baiyinchagan Depression are evaluated. The evaluation indicates that this depression is surrounded by oil and gas enrichment. The main fault and its controlled slope are the areas for oil enrichment, while Baiyin-Wengte fault zone is the main area fir the oil accumulation. In combination with the practical oil exploration in recent years, the paper concludes reservoir model and oil enrichment law in Baiyinchagan Depression.