Shale Oil Enrichment Law And Favorable Interval Prediction Of The Fourth Member Of Shahejie Formation In Damintun Depression

The fourth member of Shahejie Formation in Damintun Sag has good shale oil exploration and development potential.And the current research on lithofacies identification of shale oil reservoirs and the main controlling factors of shale oil enrichment in this section is relatively weak,which restricts the selection of favorable intervals for shale oil.In this thesis,based on petrology,petroleum geology research techniques and means,and on the basis of the lithofacies division of the shale oil reservoir in the fourth member of Shahejie Formation in Damintun Sag,systematically evaluate the characteristics of shale oil reservoirs,occurrence states and mobility characteristics of shale oil in different lithofacies,and finally clarify the enrichment law of continental low-mature shale oil in the fourth member of Shahejie Formation in Damintun Sag,and predict shale oil Favorable distribution interval.The research results of the dissertation are as follows.The organic matter abundance of the fourth member of Shahejie Formation in Damintun Sag is between 0.39%and 12.08%.The types of organic matter are mainly type I and II1,and the maturity is between 0.5%and 0.8%.It is a typical continental low-maturity shale oil.Based on the characteristics of rock lithology,structure and mineral composition,the shale oil reservoirs in the fourth member of the Shahejie Formation are divided into lamellar felsic shale,lamellar mixed shale,massive clayey mudstone,massive felsic shale There are six lithofacies:mudstone,massive mixed mudstone and massive dolomitic mudstone.（1）Laminated felsic shale,the porosity is between 2.89%and 3.98%,with well-developed bedding micro-fractures,intercrystalline pores,dissolution pores and organic pores,with good pore connectivity and oil-wetting properties;（2）The lamellar mixed shale is dominated by clay shrinkage fractures and bedding fractures,with a porosity of about 2.2%and oil-wetting properties;（3）The porosity of massive clay mudstone is about 3.37%,the reservoir space is dominated by clay intercrystalline pores and organic pores,and it is lipophilic and wettable;（4）The massive felsic mudstone has a porosity of about 2.61%,and the reservoir space is dominated by structural fractures,clay intercrystalline pores,and organic pores,with neutral wettability;（5）The porosity of massive mixed mudstone is about 2.82%,and the storage space is dominated by intercrystalline pores and organic matter,with neutral wettability;（6）Massive dolomitic mudstone reservoirs are highly heterogeneous,with porosity ranging from 1.25%to 6.64%,mainly developed dolomite intercrystalline pores and dissolution pores,with poor inter-pore connectivity and hydrophilic wettability.The occurrence state and mobility characteristics of different lithofacies shale oil were systematically evaluated by low-temperature nitrogen adsorption,saturated hydrocarbon gas chromatography and nuclear magnetic resonance testing techniques.The shale oil enrichment space of the fourth member of the Shahejie Formation is mainly distributed in the meso-micropores with a diameter of less than 10nm,and a small amount of shale oil occurs in the mesopores with a diameter of 10-100nm.Laminated felsic shale has a saturated hydrocarbon content of about 35%,and less saturated hydrocarbons below C₂₇.The shale oil has the best mobility,and the free fluid saturation is greater than 20%.Shale oil mainly occurs in pores smaller than 10 nm.middle;The saturated hydrocarbon content of massive clayey mudstone is about 60%,the saturated hydrocarbon below C₁₉is less,the oil content is about 37%,the free fluid saturation is less than 10%,the mobility is poor,the dissolution pores are developed,and the shale oil is mainly provided.exists in pores of 2 to 50 nm;The saturated hydrocarbon content of massive dolomitic mudstone is between 30%and 60%,mainly low-carbon hydrocarbons below C₁₉,with poor oil content,less than 20%,and free fluid saturation less than 5%.The mobility of shale oil is the worst,and the pores are well developed.Shale oil mainly occurs in the pores of 2-100 nm.Based on the geochemical parameters,reservoir characteristics,occurrence state and mobility characteristics of shale oil in different lithofacies,the shale oil in the fourth member of Shahejie Formation in Damintun Sag is divided into strong hydrocarbon expulsion type,weak hydrocarbon expulsion type and near source charge type.Three types of injection.The lithofacies mainly developed in the shale oil of strong hydrocarbon expulsion type are laminar felsic shale,and the light components have been expelled a large amount of hydrocarbons;The lithofacies mainly developed in the weak hydrocarbon expulsion type shale oil are massive clay mudstone,and a small amount of light components have been excreted;The proportion is high,mainly from the charging of adjacent shale oil.Based on the shale oil enrichment law and spatial distribution characteristics,three favorable distribution intervals for shale oil in the fourth member of Shahejie Formation in Damintun Sag are proposed:（1）The thick laminar felsic shale in Form I of the fourth member of the Shahejie Formation is relatively limited in distribution;（2）The massive dolomitic mudstone of Shahejie FormationⅡadjacent to lamellar felsic shale is mainly thin and widely distributed in many places;（3）The massive clay mudstone of the fourth member of Shahejie FormationⅢis interbedded with the massive dolomitic mudstone,which is widely distributed and widely seen in many places.