Hydrocarbon Source Correlation And Exploration Of Reservoir Control Factors Of Puwei Area In Dongpu Depression

Dongpu Depression locates in Bohai Bay basin and is quite abundant in oil gas resources.As the richest and top-producing area,the reserves in Puwei region account for more than 30% percent of the region's total third-level reserves.The current exploration shows that the distribution of oil gas is very complex and the controlling factors of the accumulation remains a topic of research.It has much significance for the succedent exploration to probe into the oil gas source and its controlling factors.So,based on the exploration achievements and the geochemical data,this thesis tries to make an analysis of the controlling factors from the origin of organization and summarize the pool formation pattern so as to make a conclusion of the accumulation model,making use of the approaches of geochemistry and geographical analysis.(1)The mixture of source rock is a widespread phenomenon in Puwei Region and the various proportions result in different geochemical indexes.The crude oil in Es1 comes from the mixed hydrocarbon supply of the source rocks in Es1 and Es3,but some oil is supplied only by Es1;the crude oil in Es2 and Es3 of Pucheng comes from the mixed hydrocarbon supply of several source rocks in Pucheng sub-depression and Puwei sag.In Wenmingzhai-Guyunji,the oil in Es3 and Es4 is supplied by Es3 and Es4 source-rock in the northern Weicheng sub-depression.(2)There are significant differences in natural gas geochemistry in the Puwei area,coal gas and oil gas and mixed gas all appear in this area:There are natural gas distributions in the south of Pucheng City,the northern part of Weicheng sub-fence and Hubuzhai.The amount of natural gas and carbon isotope in different beds as well as that in different regions differs a lot.The amount of methane varies from 63.74% to 94.63% while the amount of methane isotope varies from-42.3% to-28.4%.These various geochemical indexes are closely connected with diverse genetic types of natural gas.Among them,the natural gas in Hubuzhai belongs to coal-related gas,and there exist deep fractures connecting Permian-Carboniferous system,which forms the accumulation by making coal-related gas move to the reservoir.The Weicheng area is a mixed gas reservoir,where the oil-type gas from the Shahejie Formation is mixed with the coal-type gas from the Carboniferous-Permian system.In Pucheng,there co-exist coal type gas and oil type gas-the natural gas in Es2 belongs to the oil type while that in Es3 belongs to the coexistence of the two types,which reflects the connections between gas and deep fractures.(3)The distributions of oil gas in Puwei Region are mainly influenced by four factors-hydrocarbon source rock,deposited reservoir,cap rock(salt bed)and fracture.The two chief sets of source rock provides material basis for the reservoir development that is controlled by the horizontal distribution and the organic content:horizontally,the oil gas develops along the two main hydrobarbon generation sags;vertically,oil gas gathers near the good-quality hydrocarbon source strata(Es3).The differential accumulation of oil gas in the research area is controlled by the depositional facies types and the physical characteristics.In macrocosm,the outer front sub-facies of braided river delta and those of meandering river delta are the advantageous sedimentary;In microcosm,high-porosity and high-permeability reservoirs are favorable accumulation area.There mainly exist two sets of cap rocks—the salt bed in the Es1 and the combination of salt bed and thick mud.The former set develops in the transitional zone between Pucheng's sub-depression and Puwei but disappears in Weicheng sub-depression that plays an important role sealing the oil gas in Es2 and preventing the oil gas from Es3 moving to Es1.While the latter set develops in the Weicheng's sub-depression that accumulates a lot of oil gas in Weidong fracture under the influence of cap rocks.