The Compositions Of Supercritical CO₂ Extraction Products And The Occurrence State Of Retained Oil In Organic-rich Shales

At present,there are numerous oil and gas wells in the lacustrine Paleogene shale formations in the eastern basin of China,but many wells'industrial oil flows are not stable.This article selects shale oil samples and rock samples of the Qianjiang Formation's Qian 3⁴ cadence layer as the research object,and simulates supercritical CO₂ extraction under formation conditions,and combines with molecular dynamics simulation results to explore the mechanism of supercritical CO₂ extraction and the relationship between various extracted rock samples and extraction effects.It can provide the comprehensive evaluation of shale oiliness and crude oil admissibility.It is important to evaluate the oil bearing property of oil shale and exploit the oil shale reservoirs.The paper mainly designs the supercritical CO₂ extraction experiment process,and uses the geochemical analysis technologies,such as rock pyrolysis analysis,cover micropore analysis,three-dimensional fluorescence analysis,gas chromatography analysis,group composition separation analysis and so on,to analyze the extraction of oil,rock samples,extracted sample.Results show that:?1?For the shale of the Qianjiang Formation's Qian 3⁴ cadence layer,the formation temperature is about 70°C.Under simulated underground conditions,supercritical CO₂extraction experiments are performed.The optimal pressure is 30Mpa.Under this condition,the efficiency of extracting shale oil is about 69%,and the oil yield of the rock reaches 3.5mg·g^-1.?2?When the extraction ambient temperature is constant,the extraction efficiency increases as the ambient pressure increases,and the ability of CO₂ to extract heavy organic matter increases,but this change is bounded,and there is an inflection point for the best pressure throughout the process,that is when the pressure increases to a certain extent,the effect on the extraction effect of supercritical CO₂ gradually becomes smaller.When the extraction pressure is constant,the extraction efficiency gradually decreases with the increase of the ambient temperature.?3?The extraction of oil by supercritical CO₂ is mainly saturated hydrocarbons and aromatic hydrocarbons.Saturated hydrocarbons are more easily extracted than aromatic hydrocarbons,while nonhydrocarbons and asphaltenes are difficult to extract directly.Among the saturated hydrocarbon components,the light components are more easily extracted than the heavy components.?4?The effect of supercritical CO₂ extraction is positively correlated with the TOC of the rock sample and is positively correlated with the crushing degree?surface area?of the rock.The main existing state of the extracted movable oil in the shale is the free state,and the pore size is generally greater than 10 nm.