| This paper takes the characteristics of deep coal reservoirs and resources in Linxing area as the research object,based on the geological data of drilling,logging,seismic data,etc.in deep coal reservoir,combined with the coal and rock material composition,overpressure and seepage,cryogenic liquid experimental tests on nitro gen adsorption,carbon dioxide adsorption and high temperature and high pressure isothermal adsorption and desorption experiments.Taking the "coalization differentiation-hydrocarbon generation stage analysis-temperature and pressure characteristics influence-adsorption hole control-geological action control" as the main line.The development characteristics of deep coal reservoirs and coal rocks are described.The history of coal seam burial and key hydrocarbon generation periods are restored.The microscopic pore development characteristics of different scales of deep coal and rock are quantitatively characterized,and the adsorption and desorption characteristics of coal under high temperature and high pressure conditions is revealed.Additionally,the accumulation law of deep coalbed methane is analyzed,and the index system for evaluation of deep coalbed methane enrichment zone is established,which details are as folloes:(1)Based on the geological data of drilling and logging in deep coal reservoir,combined with numerical simulation research methods,the history of coal seam burial history,thermal history and coal maturity is restored,and the forming and evolution characteristics of coalbed methane reservoir is clarified.Revealing the large burial depth of deep coal reservoirs,then the objective law of the difference distribution of high temperature,pressure and coal metamorphism degree is revealed,which is the burial depth of the NO.8+9 coal seam is 1086?2158 m,with an average value of 1870 m;the coal reservoir ground temperature is 38.4?63.0?,and the reservoir pressure is concentrated at 10.0?20.5 MPa.The maximum vitrinite reflectance of coal is mainly from 1.06 to 1.5%,and it can be increased to more than 3%in the area affected by magma thermal events.The petrographic characteristics of the fluid inclusions were observed under the microscope,and the distribution law of the homogenization temperature of the inclusions was analyzed.At the same time,combined with the recovery results of the coal seam stratum history and the coal maturity history,the existence of coal seam strata was revealed.It is revealed that there are two key hydrocarbon generation periods in the coal-bearing strata in Linxing area.It is clear that the occurrence of key hydrocarbon generation period has laid a foundation for gas accumulation of deep coalbed methane in Linxing area..(2)Based on the low temperature liquid nitrogen adsorption and CO2 adsorption tests of coal,the microscopic pore development characteristics of coal is explained.It is pointed out that in the pore size range of 1.7-100 nm,the pores with a pore size of 10?100 nm mainly contribute to the pore volume of coal and the pore size of 2?3 nm mainly contributes to the specific surface area of coal pores.Quantitative analysis shows that the pore size distribution of super-microporous is bimodal in the range of 0.489?1.083 nm,the peak interval is 0.56?0.62 nm and 0.82?0.88 nm,and the specific surface area of super-microporous accounts for the total pore ratio of the adsorption pores.The surface area is 98.79?99.52%.It is concluded that under the condition of deep high pressure,the influence of super-microporous on the adsorption/desorption characteristics of deep coalbed methane plays a decisive control.The characteristics of pore volume and pore surface difference development of different metamorphic coals are described.(3)Aiming at the special geological conditions of high temperature and high pressure in deep coal reservoirs,isothermal adsorption/desorption experiments in high temperature and high pressure conditions of coal were carried out.It is revealed that the adsorption characteristics of coal rock are controlled by both the negative effect of temperature and the positive effect of adsorption pressure.The degree of metamorphism of coal affects the adsorption characteristics of coal by affecting the pore volume and specific surface area development characteristics of coal From the perspective of energy change,the analysis of the thermodynamic energy change in the process of coal adsorption of methane can be used to interpret the difficulty of coal adsorption of methane and the understanding of the control mechanism of microscopic energy change,that is,in the process of coal adsorption of methane,with temperature and the change in pressure is always accompanied by changes in microscopic energy such as adsorption potential,adsorption space,and surface free energy.It is revealed that there is desorption hysteresis effect under high temperature and high pressure conditions.The Frechet distance can be used to quantitatively evaluate the strength of the desorption hysteresis effect,and the increase of temperature will gradually weaken the hysteresis effect The applicability of various gas content prediction methods and prediction models is discussed.It is concluded that the adsorption potential theory has certain advantages in the prediction of gas content in deep coal reservoirs,that is,considering the three variables of temperature,pressure and coal metamorphism Fully reflect the influence of tiny pores of coal on the adsorption of methane.(4)The enrichment and accumulation types of deep coalbed methane are dissected in Linxing area.Revealing out that the differential distribution of gas content in deep coal reservoirs is controlled by the degree of coal metamorphism,temperature and pressure conditions and geological conditions.Five key control factors affecting the deep coalbed methane rich integration are proposed,namely coal rock adsorption characteristics,reservoir temperature and pressure,sedimentary conditions,structural conditions and hydrodynamic conditions.What is more,the indicator system for the evaluation of deep coalbed methane accumulation is established in Linxing area. |
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