Experimental And Simulation Study On Methane Adsorption Mechanism Of Organic-Rich Shale During Mature Evolution

During the mature evolution of rich-organic shale,the matter composition transformation and pore system evolution form multi-type,multi-form and multi-scale pores.The influence of these pores on methane adsorption performance and its dynamic adsorption mechanism need to be studied urgently.The thesis took the Huangxian Formation low-maturity and organic-rich oil shale as the research object.A series of different mature stage samples(series samples)were obtained through pyrolysis experiment.The characteristics of hydrocarbon generation,material composition,pore fracture and methane adsorption in different mature evolution stage were analyzed by the systematic method of experimental test-simulation study.so as to reveal the pore dynamic evolution mechanism and its control of methane adsorption performance in the maturation evolution process.The following are the main results.(1)With the increase of the temperature and pressure conditions in the thermal simulation experiment,the size and particle size of the series samples decreased gradually.The liquid hydrocarbon yield showed increased rapidly at first,then increased at slow rate and then decreased slightly at last,while the gaseous hydrocarbon yield,dominated by methane,increases gradually.The TOC content of the series samples showed a phased decrease compared with the original sample,corresponding to the evolution stage of organic hydrocarbon generation.(2)The organic matter of series samples occurred in the dispersed state with various forms.Inorganic minerals mainly include quartz,feldspar,clay minerals and carbonate rocks.The interlayer pores of clay minerals in the original samples were very well developed and contained kaolinite.The other series samples did not contain kaolinite,indicating that kaolinite was converted into illite and other minerals during the thermal evolution process.(3)The pore evolution of series samples showed obvious stage and inheritance.In the low maturation stage,the pores of organic matter are less developed.Pore system is composed of interlayer pore of clay mineral and pore of mineral matrix,which is mainly mesoporous.Under the action of pressure,the pore system is vulnerable to damage.In the mature stage,the dominant pore pores increased gradually at 1 ~ 2 nm and 50 nm.The organic matter and its hydrocarbon generation were the main material sources and mechanism of the increase of micropores.In the overmature stage,under the action of high pressure,the samples were further compacted and some pores were destroyed,forming a new pore system with slightly dominant micropore and increasing mesoporous and macropore.(4)The destruction of the original pore system in the low maturation stage caused the methane adsorption to plummet.Organic matter is the main factor affecting the amount of methane adsorption of series samples during the mature evolution process,but it is still affected by the transformation of clay minerals and the dissolution of soluble minerals.(5)The complex morphological pores produced by the mature evolution process,the more complex the morphology,the more sensitive its adsorption is to pressure.The groove space in the pore wall can improve the pore methane adsorption capacity,but the opening space of the groove space that methane molecules can enter is greater than 0.492 nm.The methane adsorption capacity of slit-pores is much higher than that of cylindrical pores.The most favorable pore size for methane adsorption is about 2 nm.In the low-temperature stage of thermal evolution,pores have strong adsorption performance but are also greatly affected by pressure,making the gas storage performance weak.In the higher stages of thermal evolution,the amount of pore absorption can decrease,but the adsorbed gas content in pores is less affected by pressure during this stage,and the gas storage performance of the reservoir is stronger and more stable.(6)The thermal maturation process was divided into compaction period,hydrocarbon generation dissolution period and high temperature and high pressure adjustment period.The compaction period is mainly affected by pressure.The primary pore system is relatively fragile,with high specific surface area and methane adsorption.Hydrocarbon generation dissolution period was mainly affected by organic hydrocarbon generation and mineral dissolution.Pore heterogeneity was enhanced.The adsorption performance was weakened,and the gas storage was good.The methane adsorption capacity was affected by multi-factor coupling.During the high temperature and high pressure adjustment period,a new pore system with slightly dominant micropore and increasing mesoporous and macropore was formed after adjustment by high temperature and high pressure.This thesis has 54 figures,13 tables,137 confrences.