Shale Oil Accumulation Mechanism And Distribution In Liaohe Western Depression

Liaohe Western Depression is a typical continental rifted basin with favorable geological conditions for shale oil accumulation.In this paper,a great quantity of experiments on shale cores,data from well drilling and logging and stimulation experiments on hydrocarbon generation were applied.Base on these data,tectonic evolution,sedimentary environment,geochemistry,mineral compositions and reservoir characteristics on different organic rich shales in Shahejie Formation were studied.Then,hydrocarbon generation and its accumulation mechanism were studied.(1)The lithology of Shahejie shales consist of dolomitic shale,silty shale,calcareous shale,carbonaceous shale and siliceous shale.Shahejie shales have the characteristic of large overall thickness and rapid change of sedimentary facies.The organic rich shales were deposited under the deep or semi-deep lacustrine facies,which can be recognized by abnormal gas logging and separation of AC and Rt.The thickness range from 30m to 150m and its distribution transferred southeastward due to the tectonic evolution.(2)The kerogen is mainly type ?-? which has the trend of oil generation in Liaohe Western Depression.The organic richness is high but affected by sedimentary environments with TOC of 1%-4%.The thermal maturity of Shahejie shales belongs to oil and wet gas zone with Ro from 0.4%to 1.2%,which related to the burial depth.Mineral composition of the shales is mainly clay with the average content of 40%-60%,and fragile mineral such as quartz content is relatively low.Shale oil reservoir has the characteristics of low permeability which varies largely due to the development of fractures and low porosity with the mean value of 6%.Various pores and micro-fractures offer abundant space for shale oil.(3)Hydrocarbon generation stimulation experiments show that organic shale with sapropel type kerogen have the highest potential of hydrocarbon generation and accumulation in maturation period.Shale oil in rifted lacustrine basins mainly distribute the center areas of sags and shales in there have high peak of oil generation,then shift to shale condensate oil or shale gas downward on profile.(4)The favored areas for shale oil accumulation in 4th member of Shahejie Formation are Niuxintuo and Chenjia.The distributions of shale oil in 3rd member of Shahejie Formation locate the Chenjia,Panshan and Qingshui sags.Qingshui sag also has the favored geological condition for shale oil accumulation of 1St and 2nd member of Shahejie Formation.This paper not only plays a positive role on development of shale oil in rifted lacustrine basins in China,but also has a certain guidance on exploration and development of shale oil in Liaohe oil field and some other areas with similar geological conditions.