Formation Conditions And Accumulation Model For Shale Oil Of The Member Es₃ And Es₄ In The Liaohe Western Depression

As a key area of continental shale oil research in China,Liaohe Western Depression has good geological conditions for shale oil accumulation.This paper takes the Member Es3 and Es4 in Liaohe Western Depression as the main study object.Using drilling,testing and logging data,and other methods,the author analyzed tectonic evolution,sedimentary environment,geochemistry,mineral compositions and reservoir characteristics on different organic rich shales.Then,shale oil formation geological conditions,oil content and accumulation model were established.Finally,the favored accumulation areas were selected using the methods of multi-factor superposition.(1)The organic rich shales in the Member Es3 and Es4 in Liaohe Western Depression were deposited under the deep or semi-deep lacustrine facies,fan delta facies and lacustrine facies,and has the thickness of 30m-150m.Shales have the characteristic of large thickness and rapid change of sedimentary facies.The lithology of shales consist of clay shale,felsic shale and mixed shale.Organic geochemical analysis and hydrocarbon generation kinetic experiments show that the organic matter of the clay shale and mixed shale(including carbonate type)have great hydrocarbon generation potential.The burial depth of the shale ranges from 2000m to 4500m and it benefits the exploitation of the shale oil accumulation.(2)Shale oil in the Member Es3 and Es4 in Liaohe Western Depression has good geochemical characteristics and physical properties.The kerogen is mainly type II₁ which has the trend of oil generation.The organic richness is high,with TOC of 1%-4%.The thermal maturity of shales is moderate,with Ro ranging from 0.4%-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.Various pores and micro-fractures offer abundant space and migration channel for shale oil.Shale oil reservoir has the characteristics of low permeability and low effective porosity,and it varies largely due to the development of fractures.(3)Shale oil ratio in the 0.14%-8.07%,with an average of 1.39%,of which the Member Es4was significantly higher than the Member Es3.The conditions of shale oil accumulation is influenced by lithofacies,organic matter abundance,thermal maturity and pore development.By establishing the accumulation model of oil shale,that shale oil accumulation law is from shale gas-shale gas condensate-shale oil changes in southern Qingshui sag buried deep area.In addition,shale oil accumulation law is from shale gas condensate-oil shale in the northern region of Chenjia sag.(4)The author improved the favorable area selection methods and standards.Considering the geological condition of shale oil accumalution,the author used sedimentary facies,development and distribution of shale,geochemistry,reservoir condition as parameters,and selected the favorable areas of shale oil.The distributions of shale oil in the Member Es3 Formation locate the Chenjia,Panshan and Qingshui sags and its surrounding area.The distributions of shale oil in the Member Es4 Formation locate the Niuxintuo sag and Gaosheng area.The research results of this paper have guiding significance for the exploration of shale oil in the study area,and can also provide reference for other regions with similar geological conditions.