Study On The Conditions For Petroleum Accumulationin The Qianliyuan Sag Of Dongpu Depression

Qianliyuan sag is the earliest subsidence in Dongpu depression,with the characteristic of complex formation,and quickly varied sedimentary facies,nearing to east provenance.It developed longitudinally three sets of salt rock in Es₁,Es₃² and Es₃⁴.The sag is characterized by deep burial,simple structural trap,various lithologic traps,and complex source-reservoir-cap assemblages.Hydrocarbon source rocks are widely distributed and mainly developed two sets of hydrocarbon source rocks.Because of deep burial depth,complex reservoir types in the Qianliyuan sag,the exploration is difficult.There is no significant breakthrough in the area.The abundant oil and gas occurrence has been found in the surrounding areas through early exploration in the whole region,and commercial and low-output oil and gas flow has been obtained in some wells.However,a large part of reserviors are still unable to increase.It is difficult to achieve greater progress in exploration.The study on the conditions for hydrocarbon generation from source rocks,reservoir development and petroleum accumulation in the Qianliyuan sag in Dongpu depression was carried out in the paper,with the integrated use of geological,geophysical and geochemical data.The characteristics of lithology and distribution of hydrocarbon source rocks were defined,and the reservoir space and diagenesis were demonstrated and the conditions for oil-gas accumulation were discussed.Through the above research,the following conclusions are obtained:?1?the organic matter abundance of hydrocarbon source rocks is higher,the type is favorable,and the thickness is larger,and they have entered oil window,the peak period of oil generation,thus they have great hydrocarbon generating potential.However,because of the existence of salt strata and the abnormal high pressure development,it will play a certain suppression effect on the thermal evolution of source rock.?2?There are three sets of sedimentary systems developed in the Qianliyuan sag.The provenance is near and the sand body with large thickness is well developed.The diagenesis of the reservoir is strong,and the secondary pores are relatively well-developed.The physical properties of the reservoir have been greatly improved.?3?There are many sets of source-reservoir-cap assemblages in the study area,and the widely distributed salt rocks provide an important guarantee for the favorable preservation of oil and gas.?4?The main types of oil and gas pathways are connected sandbodies,faults,and the combination forms of the two,and migration and accumulation of oil and gas are characterized by episodic characteristic,which is related to the commonly developed abnormal high pressure zone and fluid compartment in the study area.The fluid compartments are independent and distinct,showing a unique pressure model of Dongpu depression.?5?The oil-gas accumulation conditions and main reservoir forming types in the study area are defined,and the favorable exploration target area is optimized,which provides reference for the furure exploration.The study in this paper can improve the understanding on the oil and gas accumulation conditions and exploration potential in the Qianliyuan sag,and provide new ideas and reference for petroleum exploration in deep sag of continental basin.