Study On Micropore Characteristics And Controlling Factors Of Cretaceous Qingshankou Formation Shale In Songliao Basin

Qingshankou Formation of Cretaceous in Songliao basin is the key area for exploration and exploitation of oil and gas resources in China,but there are some problems,such as strong reservoir heterogeneity,complex sedimentary and structural background,diverse lithology,and great difference in diagenetic evolution stage.Previous studies on this area are mainly based on the macro point of view,while the research on the refinement of micro reservoir space is few,but micro nano pore space is an important channel for shale oil storage and migration,with obvious geological significance of oil and gas.Therefore,based on the collection and collation of relevant geological data in the study area,this paper systematically carried out the auxiliary experiment of shale micro pore space research With the help of advanced micro nano pore characterization methods,the development characteristics and control factors of micro pore space of shale in this interval are studied.The results show that: 1)the formation of Qingshankou Formation in the study area is developed with dark mudstone of semi deep lake deep lake facies.The type of organic matter is mainly sapropelic type I,with high abundance.It is in the stage of low maturity to maturity.The physical properties of the reservoir are poor.The porosity is between 4.6% and14.4%.The permeability is generally lower than 0.1md,with the characteristics of low porosity and ultra-low permeability.The correlation between the saturation index of nuclear magnetic oil and the total porosity of nuclear magnetic resonance The relationship shows that the minimum porosity limit of shale oil reservoir in this interval is 8%;2)the micro pore type of shale is complex,and there are skeleton mineral intergranular pore,intergranular pore,clay mineral intergranular pore,mold pore,organic plasmid inner thermolysis pore and edge fracture,diagenetic bedding fracture,structural microfracture,dissolution microfracture and diagenetic contraction fracture,among which the diagenetic bedding distributed along the layer is developed On the basis of fractures,with structural micro fractures as the main channel and micro nano pore space as nodes,they form a complex four-stage pore network connection system,in which shale oil occurs in a free state;3)the pore diameter ofmicro storage space is generally small,the whole body is mainly composed of micro pores and transition pores,followed by medium pores,with the least large pores,in which the pore size is 10-100 nm There is a good positive correlation between the transition pore and the nuclear magnetic oil saturation,which is the most important type of shale oil reservoir space in this interval.The evolution of the pore fracture system in this interval roughly goes through the primary intergranular pore development stage and the primary secondary pore development stage.The porosity generally decreases with the deepening of the burial depth,and three more obvious vertical ones are formed Secondary pore development zone;4)the formation and evolution of micro pore space are controlled by sedimentation and diagenesis,which controls mineral composition and maturity of rock structure and directly affects the type and characteristics of micro pore space of reservoir;diagenesis controls the evolution form and state of micro pore space,in which mechanical compaction leads to deformation,contraction and cementation of pore space The physical properties of the reservoir are improved by expanding the pore space and increasing the number of pores.