Assessment Of Shale Oil Potential And Prediction Of Movable Oil Of The Upper Jiufotang Formation In Ludong Sag,KaiLu Basin

Ludong sag is a part of Lujiapu depression,a secondary negative structural unit in the Kailu basin,Inner Mongolia,where two main oil-generating sub-sag,Jiaolige and Sanshifangdi,are developed.The shale in the upper member of Jiufotang Formation is widely distributed with large thickness,high organic matter abundance,and good organic matter type.However,in the past,a few studies have been carried out on the Jiufotang Formation only from the perspective of source rocks,and barely work focused on shale oil has been conducted.Taking the shale of the upper member of Jiufotang Formation in Ludong sag as the research object,through the study of geochemical characteristics,paleoenvironment,shale oil-bearing property,and shale oil mobility,this paper establishes the shale oil enrichment model and predicts the shale oil resources of it,and the following understanding has been obtained:The difference of paleoenvironment between Jiaolige and Sanshifangdi sub-sag has been put forward.The organic matter of shale in Jiaolige sub-sag derived from algae,the sedimentary environment is a weak oxidation to weak reduction environment with a saline water body.Paleo-productivity,redox environment,and sedimentation rate controlled the enrichment of shale organic matter jointly.However,the shale organic matter in Sanshifangdi sub-sag was algae and higher plants,of which the sedimentary environment is an oxidation-weak oxidation freshwater environment.The salinity of the water in the center of the sag is greater.Paleo-productivity is the main controlling factors for the enrichment of shale organic matter.The hydrocarbon-generating evolution model of shale organic matter in Jiaolige sub-sag and Sanshifangdi sub-sag has been proposed.The thermal degradation process of shale organic matter in Sanshifangdi sub-sag follows the Tissot kerogen hydrocarbon generation model.There are two hydrocarbon generation evolution processes in the shale of Jiaolige sub-sag,which are low mature oil generated at early low temperature from bio-lipids and thermal degradation oil generated in the oil generation window.The difference in hydrocarbon generation evolution characteristics between depressions is affected by the organic matter sources and paleoenvironmentThe oil-bearing property of shale has been systematically evaluated.Based on the restored model of chloroform asphalt "A" and S1,the amount of oil retained in the upper member of Jiufotang Formation shale has been quantitatively evaluated as 0.05%-0.91%(chloroform asphalt "A")and 1-14.26 mg/g(Si).The results of retained oil calculated by the Si hydrocarbon recovery model is too large.TOC,maturity,lithofacies,porosity and hydrocarbon expulsion efficiency are the influencing factors of oil-bearing property.The oil-bearing property of laminated shale is relatively good,and the oil-bearing property of layered silty shale is greatly affected by the distribution characteristics.The differential shale oil accumulation model of the Jiaolige sub-sag and Sanshifangdi sub-sag has been established.Lithofacies,maturity,and oil-bearing property are the main controlling factors of shale oil accumulation.The center of sub-sags are dominated by free hydrocarbon-rich matric shale oil.A small amount of low mature oil is developed in shallow massive silty shale of Jiaolige sub-sag.Free hydrocarbon-poor matrix shale oil developed from the lower depth of Sanshifangdi sub-sag center.And,from the southeast steep slope zone to the center of the sub-sag,the accumulation form of free shale oil changed from fracture type to matrix type.Moreover,The total movable oil ratio of upper Jiufotang Formation shale varies from 12.815%to 17.137%,and the amount of movable oil varies from 0.704?2.693×10-3t/m2.The shale oil resources in the upper member of Jiufotang Formation are predicted to be 1.4459×108t by using chloroform asphalt "A" parameter method,and the movable resources of shale oil are 0.18X 108t.This paper studies the oil-bearing property,accumulation model and shale oil resources of the shale in the upper member of Jiufotang formation and enriches the basic geological theory of continental shale oil which has a certain significance for Chinese shale oil exploration in small to medium-sized continental basins.