Study On The Evolution Law And Reaction Process Of Pyrolysis Products Under The Conditions Of Oil Shale In-situ Conversion

Oil shale belongs to unconventional oil and gas resources,and the effective development of oil shale resources can alleviate the energy crisis all over the world.Kerogen rich in oil shale belongs to immature stage,which can produce pyrolysis oil and pyrolysis gas under heating condition.At present,the development technology of oil shale is mainly divided into surface retorting and in-situ conversion.Surface retorting has been used for a long time in China,mainly for heating and power generation,while surface retorting mainly uses oil shale in shallow strata,which limits the available oil shale resources,On the other hand,the surface retorting method of oil shale causes air pollution,water pollution,waste residue pollution and other environmental problems,so the surface main stream of oil shale can not be used for a long time on a large scale.In recent 20 years,the in-situ conversion of oil shale resources with huge resources and deep strata has become a research hotspot.In recent years,the oil shale research team of Jilin University has carried out pilot tests on in-situ conversion of oil shale in Nong'an and Fuyu.It is found that the organic matter evolution of oil shale char,pyrolysis gas and pyrolysis oil at different heating stages under high pressure and the hydrocarbon generation potential of oil shale at each reaction stage are very important for the effective in-situ conversionengineering of oil shale and the utilization of shale oil and gas products.Moreover,the evolution degree of organic matter and hydrocarbon generation in different experimental conditions and different stages are often defined by the Ro value and T_maxvalue of core experiment.However,in the actual in-situ conversion experiment engineering,oil shale rock samples can not be obtained,and only the pyrolysis oil and gas produced by oil shale pyrolysis can be obtained by using the production wells,so the Ro value and T_maxvalue of pyrolysis oil shale semi-coke cannot be determined.Due to the heterogeneity of organic matter distribution in oil shale and different heating degree in in-situ conversion experiment engineering,it is difficult to determine the degree of organic matter conversion in underground oil shale according to heating temperature and heating time,which brings many uncertain factors for mining and leads to the waste of energy.Therefore,it is of great practical significance to seek geochemical control methods that can indicate the evolution process of organic matter in the process of oil shale in-situ conversion production.In order to further study this problem,two oil shale core samples from Songliao Basin in Jilin University are selected for high-pressure heating experiment,and the block core is subjected to high-pressure heating experiment by adopting the technology method of simulating field engineering,which is consistent with the underground construction environment and construction technology.The experimental results show that the pyrolysis process of oil shale can be divided into three stages:room temperature?300?,300?475?and 475?520?.At 300?475?,the main product discharged from oil shale is pyrolysis oil,and the production is significantly increased compared with the first stage.Methane is the main hydrocarbon gas,and the methane percentage in the samples above 450?is higher than 90%.Part of the shale oil produced by oil shale pyrolysis remains in the oil shale pores,while some is discharged from oil shale pores and fractures.The proportions of non-hydrocarbon components(NSO)and asphaltenes in the shale oil remaining in oil shale exceed those of saturated and aromatic hydrocarbons and reach a peak at 350?.In the later stage,shale oil generation rapidly increases,which is discharged,and the saturated hydrocarbon content in the discharged shale oil is the highest.Non-hydrocarbons and asphaltenes may be intermediate products in the kerogen conversion process into shale oil,which may block oil shale pores at approximately 350?.However,with increasing heating temperature,pores reopen and expand during pyrolysis generating small-molecule hydrocarbons.Oil shale sample pyrolysis at low temperatures attains a good hydrocarbon generation potential,and 425?450?represents a turning point.Oil shale pyrolysis at temperatures above 450?exhibits a low hydrocarbon generation potential.This temperature node is very important for downhole temperature selection and control in oil shale in situ mining engineering.In the fourth chapter,the study on the maturity parameters of organic matter in the pyrolysis process of oil shale shows that the interaction diagram of in C1/C2 and in C2/C3 in the hydrocarbon gas produced by pyrolysis determines the maturity change of kerogen and presents a good rule,which can prove that the maturity of kerogen is constantly improving.The Ro value of core samples increases with pyrolysis temperature,which shows that the maturity of kerogen is from immature to mature.T_maxcan only be applied to the samples whose pyrolysis temperature is below450?and can indicate the maturity of organic matter in immature low mature-mature oil shale.With the increase of pyrolysis temperature,the main peak carbon and CPI value of saturated hydrocarbon decrease gradually.For the biomarkers of pyrolysis oil,it is found that Ts/(Ts+Tm),hopane C₃₂22S/(22S+22R),sterane C₂₉20S/20(R+S)and??/(??+??)have a good trend with the increase of pyrolysis temperature.The organic matter maturity process of oil shale from the original sample to the pyrolysis temperature of 425?has a good indication,and the differentiation is obvious and covers the main pyrolysis hydrocarbon generation peak.The study of stable carbon isotope of organic matter shows that it is necessary to study the stable isotope fractionation of oil shale in the same section of a specific area,and then comprehensively analyze the total oil carbon isotope and each component carbon isotope to determine the degree of organic matter pyrolysis.Therefore,this study suggests that the pyrolysis oil and gas can be obtained by opening the production well in the oil shale in-situ production engineering,and then the pyrolysis process of oil shale organic matter can be effectively tracked and controlled by a variety of maturity parameters.It is suggested that the temperature of downhole heater should be set at about 425?in order to obtain the maximum energy return.In the fifth chapter,through the previous systematic study of Nong'an oil shale and the organic geochemical analysis of the pyrolysis oil obtained from Nong'an production wells,including the parameters of the pyrolysis oil biomarkers and the stable carbon isotope of each component of the pyrolysis oil,combined with the geochemical analysis of the pyrolysis oil in this simulation experiment,the comprehensive analysis shows that the underground oil shale in the current Nong'an oil shale in-situ conversion project has the following characteristics The pyrolysis degree of organic matter in the target horizon is equivalent to the stage of 400?425?in the simulation experiment,which is at the peak of the oil generation window.The heating process currently used is in line with the engineering expected experimental purpose and has economic value.The comprehensive geochemical research method proposed in this paper will be essential for oil shale in-situ mining engineering,which should run through the whole process of decision-making and engineering process control,so as to maximize the economic rate of return.At the same time,on the basis of regional detailed resource evaluation,it is necessary to obtain the geochemical test of oil shale thermal simulation experiment system in the target mining layer,and then determine the organic matter pyrolysis process of underground oil shale.In the process of research,comprehensive study of various geochemical data should be carried out,and attention should be paid to the space-time gap of geochemical research objects.It is hoped that the research work of this paper can provide new ideas for the development of oil shale in-situ mining technology,and continuously improve it to become the key technology of oil shale in-situ conversion experimental engineering.