Potential Classification Evaluation Of Shale Oil And Predictions Of Favourable Areas In North-central Parts Of Raoyang Sag

With the daily increasing global demand for energy,the growth of conventional oil and gas production has been slow,and the contradiction between oil and gas supply and demand has become increasingly prominent.Shale oil and gas in the unconventional resources have become a research hotspot in the field of petroleum exploration.During the depositional period of Palaeogene in lower Es1 and upper Es3 submembers in the Raoyang Sag of the Jizhong Depression,the scale of lake transgression has been large and developed two sets of organic-rich lacustrine shale.The predecessors conducted lots of researches about these two sets of shale on source rocks,but little of shale oil within them had been studied and reported.Therefore,shale in lower Es1 and upper Es3 submembers in North-central parts of Raoyang Sag is studied in this paper to study shale composition heterogeneity,shale oil quantity,exploration favorable areas of shale oil and other aspects.Raoyang Sag is one of the oil-rich concaves in the Jizhong Depression.We have carried out organic geochemical analyses about shale in lower Es1 and upper Es3 submembers in North-central parts of Raoyang Sag and made targeted classification evaluations about the shale oil resources in the study area according to the"triple-division"relationship between oiliness of shale and TOC.We evaluated the shale in the study area about the organic heterogeneity according to the delta LogR model,restored the light hydrocarbon and rectified the heavy one on the pyrolysis parameters S₁ using the extraction-pyrolysis method and the dynamic theory of hydrocarbon,and calculated the quantity of the shale oil resources in the study area based on the volume method.A shale oil momentum evaluation model was established to predict the recoverable quantity of shale oil in the target zone of the study area.Based on the whole rock analysis data of the shale sample in lower Es1 submember,a variety of log curves and the principle of multi-component response superposition were used to fit and predict the brittle mineral content of shale in lower Es1 submember.According to the actual conditions in the study area,optimal criteria of favorable areas fitting for shale oil exploration in the study area are formulated.The following conclusions can be reached:the abundance of organic matter of shale in lower Es1 and upper Es3 submembers is medium,the types of organic matter are fair,including type II₁ and II₂ predominantly,and the organic matter maturity is mainly in low mature and mature stages.The results show that the total quantity of shale oil in lower Es1 submember is3.006 billion tons.Class I resources are 1.297 billion tons,Class II resources are 1.022 billion tons,and Class III resources are 687 million tons.The quantity of recoverable shale oil in lower Es1 submember is about 1.202 billion tons,accounting for 40%of the total more or less.The total quantity of shale oil in upper Es3 submember is 1.714 billion tons,Class I resources are1.002 billion tons,Class II resources are 521 million tons,and Class III resources are 191million tons.The quantity of recoverable shale oil in upper Es3 submember is about 0.7 billion tons,almost accounting for 41%of the total.In this paper,the reference standard of favorable areas selection is:the continuous thickness of shale is over 30m,the organic carbon content is respectively more than 1.7%in lower Es1 submember and more than 1.1%in upper Es3submember,the brittle mineral content of shale is over 35%and the intensity of recoverable oil is more than 60×10⁴ t/km².In general,the total square of favorable areas for shale oil in lower Es1 submember is about 377 km²,while the total quantity of recoverable shale oil is about 0.47billion tons.The total square of favorable areas for shale oil in upper Es3 submember is about118.761 km²,while the total quantity of recoverable shale oil is about 0.141 billion tons.