Study On Shale Reservoir Characteristics Of The First Member Of Qingshankou Formation In Changling Sag,southern Songliao Basin

In this paper,the first member of Qingshankou Formation in Changling sag,southern Songliao basin is the main target layer,which is rich in shale oil resources.Based on the analysis of shale lithofacies characteristics,organic geochemical analysis,reservoir space type and pore structure,various technical means are used to characterize the reservoir space characteristics and physical properties of shale reservoir,and comprehensively evaluate the characteristics and influencing factors of shale reservoir of Qingshankou Formation in Changling sag,southern Songliao basin.The results of core observation,X-ray diffraction and organic geochemical analysis show that the mineral components of mud shale in Qing 1 member are mainly terrigenous clasts and clay minerals,with a small amount of carbonate rock and pyrite,showing the characteristics of low clay and high brittle mineral content;The abundance of organic matter was high,and the highest TOC was 3.115%,with an average of1.453%.The average value of S₁+S₂is 5.89mg/g,with good hydrocarbon generation potential.It belongs to general good source rock.The type of organic matter is mainly II1,followed by II2;The sedimentary structures are mainly massive and laminar;Because there is no significant difference in the mineral composition of shale in the first member of Qinghe formation in the study area,taking the organic matter content and sedimentary structure as the main factors,this paper identifies four main lithofacies in the first member of Qinghe formation:high organic matter massive mudstone,medium organic matter massive mudstone,medium organic matter laminar shale and low organic matter laminar shale.The results of field emission and high-resolution backscatter scanning electron microscope show that the reservoir space of shale reservoir includes pores and fractures.Among them,pores include intergranular pores,intergranular pores,dissolution pores and organic matter pores,and organic matter filling is common in fractures;The pores of the reservoir are mainly in nano micron scale,and the number of pores decreases exponentially with the increase of pore size.The inter granular pores and dissolution pores have a large face rate and a large number of pores,which are the main reservoir space.The surface porosity of different lithofacies varies greatly.Among them,the surface porosity of layered shale with medium organic matter is the highest,with an average face porosity of 3.53%.The pore area is mainly provided by intergranular pores and dissolution pores,followed by intergranular pores and organic matter pores;The second is high organic matter massive mudstone facies and low organic matter laminar shale facies,with an average face rate of 1.74%and 1.38%respectively.The pore area is mainly provided by intergranular pores and dissolution pores;The face porosity of medium organic matter massive mudstone is the lowest,with an average face porosity of 0.13%.The pore types are mainly intergranular pores and intergranular pores,and a small amount of organic matter pores are developed.The results of nitrogen adsorption and porosity and permeability show that the nitrogen isothermal adsorption curves of Qingyi shale are H3 type,the pore structure is mainly parallel plate pores,and the pore diameters of the samples are less than 200 nm.The mesopores are mainly 20-50nm,accounting for 56%-63%;The second is the macropores larger than 50nm,accounting for 36%-40%,the average specific surface area is 12.6955%,and the average pore volume is 0.04876cm3/g;The average porosity is 1.26%and the average permeability is 0.021md.Among them,the porosity of high organic matter massive mudstone phase is the largest,which is 2.31%,and the permeability of medium organic matter massive mudstone phase is the largest,which is0.05306md.Combined with the analysis of face rate,pore volume,porosity and permeability parameters,the pore structure of medium organic matter laminated shale facies is the best,followed by high organic matter massive mudstone facies,and the medium organic matter massive mudstone facies and low organic matter laminated shale facies are the worst.The shale reservoir of Qingyi member is affected by many factors,such as organic matter hydrocarbon generation,diagenesis and tectonism.Among them,mineral composition,organic matter hydrocarbon generation and diagenesis have obvious effects on reservoir physical properties;If the content of terrigenous clasts is high and the content of carbonate is low,the physical properties of the reservoir are good,which is positively correlated with the content of quartz;The influence of organic matter on reservoir physical properties is mainly through the reduction of its own volume caused by hydrocarbon generation and expulsion,the formation of shrinkage fractures or internal micro fractures,and the release of organic acids by hydrocarbon expulsion of organic matter,which is conducive to dissolution and the formation of gaseous hydrocarbons and micropores by organic matter in the mature stage,so as to improve the reservoir;Diagenesis has complex and multifaceted effects on reservoir physical properties.Clay mineral transformation,compaction,dissolution and cementation will lead to changes in mineral composition in the reservoir,formation of new secondary pores,redistribution of micro and nano pores,and significant changes in pore structure.Judging by RO and burial depth,the samples are in phase a of medium diagenetic evolution,The main diagenesis stage is the transformation and dissolution of clay minerals;Fractures produced by tectonism,especially natural fractures,can effectively improve reservoir permeability.Because the sample pores are mainly intergranular pores and dissolution pores,cementation is not conducive to the preservation of pores,and dissolution plays a good constructive role in shale reservoir space.The evolution of hydrocarbon generation of organic matter improves the physical properties of shale gas reservoir and makes up for the loss of inorganic pores in the process of burial compaction.