Analysis Of Oil-content And Mobility Of Intersalt Shales In The Qianjiang Formation,Qianjiang Depression,Jianghan Basin

Terrestrial shale in China has rapidly changed sedimentary facies and greatly varied burial depths.Strong heterogeneity can be seen in organic matter type,maturity,and storage space of continental shale reservoirs.Thus,the geological evaluation method of continental shale oil can be different from that of North American marine shale reservoirs.At present,the existing experimental technology is mainly developed for the exploration of conventional reservoirs.There is still lack of study on the retention mechanism,occurrence,and accumulation conditions of oil in terrestrial shale reservoirs.Besides,the evaluation method of shale oil is not yet available due to the lack of scientific experimental method and reliable experimental data.In this paper,the shale oil in Q ianjiang Formation of Jianghan Basin is studied.A three-dimensional fluorescence quantitative analysis technology and a frozen fragmentation pyrolysis analysis technology are established to qua ntitatively characterize the oil content in Q ianjiang Formation.Using the combination of optical observation and chemical anatomy,the occurrence of inter-salt shale oil is revealed.By applying the solvent step extraction method and multi-temperature thermal release method,a quantitative characterization of shale oil in different occurrence states in Qianjiang Formation is performed.The mobility of inter-salt shale oil is evaluated.The oil saturation index(S₁/TOC),combined with pyrolysis movable oil volume(S_1-1)and three-dimensional fluorescence quantitative techniques,is used to evaluate the mobility of inter-salt shale oil.Based on the previous research results of the collection space,the inter-salt shale oil storage mode,detention mechanism and the enrichment mode are also clarified.The study found:(1)high oil content can be found in the 10th rhythmicic Eq3⁴member in the depth of 2820 m?2823 m.Different oil content can be seen in different intervals in Eq4 member.O verall,Eq4 member has huge exploration potential of shale oil.(2)shale oil in the 10th rhythmicic Eq3⁴ member mainly exists in the intergranular pores of carbonate rocks.The trapped oil mainly exists in absorbed and adsorbed state in kerogen and the free oil mainly exists in the inorganic mineral pores.(3)the oil content of inter-salt shale is closely related to the petrographic characteristics,abundance of organic matter,reservoir physical properties,and the sealing capabilities of source rock of Q ianjiang shale Formation.(4)high free oil content of Q ianjiang Formation can be found through experimental analysis in this study.Shale oil migration is dominated by the inner migration of the same rhythm layer,and the vertical migration is not obvious.It is finally proposed that there are mainly two inter-salt shale oil enrichment modes in Q ianjiang Formation,named A and B.Mode A mainly exists in the Wangchang structural development area whereas Mode B mainly exists in the hydrocarbon-generating depression area.Oil and gas accumulation are closely related to the source rocks,reservoir conditions,and Formation pressure conditions.The stratum development layer is the most favorable layer for the migration of mature oil and gas along fractures.