Evaluation Of Shale Oil And Gas Resource Potential Of Typical Basins From The United States

The successful development of tight oil from the Bakken Formation in the Williston Basin and the shale oil from the Eagle Ford Formation in the Western Gulf Basin have made shale oil and tight oil an outstanding area for the exploration and development of unconventional energy resources.The enrichment of oil and gas in shale is not only related to the hydrocarbon generation potential of shale,but also closely related to the efficiency of hydrocarbon expulsion.Therefore,in order to evaluate the shale oil and gas potential of four basins from the United States,the characteristics of hydrocarbon generation and expulsion of them are studied.This paper relies on the well log and geochemical database of American typical basins(Williston Basin,Permian Basin,Denver Basin,and Western Gulf Basin)provided by the Global Oil and Gas Resource Evaluation and Exploration Planning Institute of the China Petroleum Exploration and Development Institute.Hydrocarbon generation potential and hydrocarbon expulsion efficiency of shale were studied.Based on this,the relationship between movable oil volume and hydrocarbon expulsion threshold in shale was analyzed,which provided the basis for optimizing oil and gas favorable intervals in typical shale gas-bearing combinations in the United States.In this paper,the abundance,type and maturity of organic matter in typical basins of the United States were analyzed,and hydrocarbon generation and the thermal evolution of source rocks were quantitatively evaluated using the chemical kinetics method.Shale organic heterogeneity evaluation method was used to classify shale oil/gas resource potential.Two different methods were selected to calculate the hydrocarbon expulsion efficiency of different types of shale,and ultimately determine the corresponding movable oil limit standard based on the hydrocarbon expulsion threshold.The results show that the organic carbon content of shale from the Williston Basin is generally higher than that of other basins,especially the Bakken Formation has the best hydrocarbon generation potential,whose organic matter types are mainly Type I and Type II,and the yield index is high and rich in oil production.Both the Upper Bakken Formation and the Lower Bakken Formation are in the oil production stage,and the oil content is large.The TOC limits of dispersed(invalid)resources,inefficient resources and enriched resources of Bakken Formation in Williston Basin are 4%and 10%respectively,and the corresponding S₁ limits are 2mg/g and 6mg/g respectively.Wolfcamp Formation in Permian Basin has the TOC limit of 1%and 3%respectively,and the corresponding S₁ limit of 0.6mg/g and 2.5mg/g respectively.The TOC boundary of Niobrara Formation in the Denver Basin are 3.2%and 11%respectively,and the corresponding S₁boundary are 21.2mg/g and 3.5mg/g respectively.The hydrocarbon expulsion threshold for type I organic matter in the source rock of the Bakken Formation in Williston Basin is 2200m,2400m for Type II₁,and 2750m for Type II₂,while Type II₁ organic matter in the source rock of the Niobrara Formation in Denver Basin is located at 1900m,and Type II₂ is 1950m.The better the organic type,the shallower the hydrocarbon expulsion threshold.According to the hydrocarbon expulsion threshold,the movable oil standard in the Bakken Formation from the Williston Basin is 75 mg/g·TOC,while the Niobrara Formation in the Denver Basin is75mg/g·TOC.The potential of shale oil and gas resources of the Western Gulf Basin is the largest,with an oil production of 401.3×10⁸t,residual oil of 313.6×10⁸t and discharge oil87.7×10⁸t.The lower part of Bakken Formation from the Williston Basin takes the second place,with an oil production of 315.7×10⁸t,residual oil of 91.9×10⁸t and discharge oil 223.8×10⁸t...