| As a kind of unconventional oil and gas resources,shale oil has huge reserves.It can be used as an important substitute resource for oil and has great exploration and development potential.Many sets of organic rich shales with different lithofacies are developed in the first member of the Qingshankou Formation in the Songliao basin.Taking the shale sedimentary environment and reservoir characteristics of the first member of the Qingshankou formation as the research object,this paper aims to reveal the enrichment law of shale organic matter and reservoir performance of different lithofacies,so as to provide guidance for the subsequent exploration and development of shale oil in this area.By means of core and thin section observation,petrological and mineralogical analysis,organic geochemical analysis and quantitative characterization of reservoir pore structure,this paper comprehensively studies the lithofacies characteristics,sedimentary environment and reservoir characteristics of shale in the first member of the Qingshankou formation.Gain the following understanding:（1）The main lithofacies types of shale in the first member of the Qingshankou formation are black shale facies,massive mudstone facies,laminar mudstone facies and silty mudstone facies.The organic matter abundance of black shale facies shale is the highest,and the type of organic matter is mainly type I,which is in the stage of low mature oil generation window and has the greatest hydrocarbon generation potential;The organic matter types of massive mudstone facies and laminar mudstone facies shale are mainly mixed with type I andⅡ1,and their hydrocarbon generation potential is similar,second only to black shale facies;The organic matter content of silty mudstone facies shale is low,and the type of organic matter is mainly typeⅡ2.Compared with the former,it belongs to the source rock with the worst hydrocarbon generation potential.（2）By studying the sedimentary structure and biomarker characteristics of different lithofacies,it is found that terrigenous input,hydrodynamic conditions,water salinity and redox will affect the enrichment and preservation of organic matter in shale.During the depositional period of the Qingshankou Formation in the Songliao Basin,the climatic conditions were warm.At the same time,affected by seawater intrusion,the water body deepened,the initial productivity increased,and the bottom of the lake basin changed to a high salinity anoxic reduction environment,which provided conditions for the enrichment of organic matter in the study area.The mud shale of the first member of the Qingshankou formation is deposited in the anoxic environment of reduction weak reduction.Black shale is mainly formed in the reduction environment of deep lake and semi deep lake,and the organic matter mainly comes from algae,bacteria and other low aquatic organisms;Massive mudstone is also formed in the semi deep lake deep lake environment,and the source of organic matter is aquatic plankton and a small amount of terrestrial plants;The laminar mudstone is formed in the shore shallow lake semi deep lake environment,and the source of organic matter shows the characteristics of the mixing of terrestrial higher plants and lower aquatic organisms;The silty mudstone is generally deposited in the shallow water environment of delta front shore shallow lake,and the organic matter mainly comes from terrestrial higher plants and a small amount of aquatic organisms.（3）The pore size of shale in the first member of the Qingshankou Formation in the Songliao basin is distributed in the range of 0.4nm～200nm,and micropores and mesopores are the most developed.Black shale has the best degree of micropore development,with an average micropore volume of 9.69ml/kg,accounting for 11.87%of the total,providing the maximum specific surface area（average 23.06m2/g）,and providing a large number of storage places for adsorbed shale oil;The micropore development degree of massive mudstone and laminated mudstone is close,but they are lower than that of black shale.They have similar pore volume,specific surface area and average pore diameter;In contrast,silty mudstone has the worst micropore development and better mesoporous development.Clay minerals are the main controlling factor for the development of pore structure of the Qingshankou Formation shale,especially the development degree of microporous and partial mesoporous pores has an obvious positive correlation with the content of clay minerals.Clastic minerals contribute to the development of larger pores in shale.There is no obvious correlation between organic matter content and pore structure parameters.（4）In the sedimentary period of the Qingshankou Formation shale,due to the deepening of water body,the reduction of terrigenous input and the increase of clay mineral content,the difference of pore structure under different lithofacies is controlled.In the initial stage of sedimentation,the lake basin is shallow,with strong hydrodynamic force and more terrigenous input,forming silty mudstone with poor micropore and pore development;In the middle stage of sedimentation,the water body deepened and the lake basin changed to a deep lake semi deep lake environment.At this time,the hydrodynamic force weakened,the terrigenous input decreased,the content of clay minerals increased,and the development of micropores gradually improved,forming laminated mudstone and massive mudstone;At the end of Lake Basin expansion,the maximum Lake flooding surface is reached,the water body is relatively calm and stable,and the depth reaches the maximum.At this time,clay minerals become the main body of sedimentary minerals,and finally form black shale with the best microporous pore structure. |
