Time effect laws of pore structure evolution in anthracite reservoirs under the action of supercritical CO2
CO2 geological storage is one of the effective technologies to achieve emission reduction and reuse of abandoned mine resources,but the change of pore structures in coal seams after CO2 injection has a time effect,and its evolution laws have a direct effect on the potential of CO2 geological storage.In order to explore the real change situations of the pore structures in coal seams with the increase of the action time and to improve the calculation accuracy of the volume of CO2 geologic storage,this paper selects the anthracite coal taken from the Nantong Mining Area of Chongqing as the research object to study the evolution laws of pore structures in the coal samples of this area at different action time of supercritical CO2 by performing supercritical CO2 adsorption experiment,low-temperature nitrogen adsorption experiment,X-ray diffraction test,nuclear magnetic resonance(NMR)test and scanning electron microscopy(SEM)test.And the following research results are obtained.First,after the action of supercritical CO2,the change in the porosity of the coal samples mainly occurs within 7 days.The porosity increases by 3.20%after 7 days of the treatment,but only by 0.05%during the 7th to the 14th day.Second,with the increase of the action time,the specific surface area of the pores in the coal samples increases,but change amplitude reduces gradually,with an average daily increase of 19.74%-24.50%within 7 days and 2.37%-4.60%during the 7th to the 14th day,and the change rule follows approximately a logarithmic function.Third,the chemical reaction between supercritical CO2 and coal leads to the dissolution of minerals,which increases the surface roughness of the coal body.The fractal dimension characterizing the roughness of the coal samples increases continuously with the increase of the action time.Fourth,the action of supercritical CO2 can effectively change the porosity and surface morphology of the coal samples,which provides more CO2 adsorption sites.The modification effect of supercritical CO2 on the pore structure is more obvious within 7 days.In conclusion,the change of the pore structures in anthracite coal under the action of supercritical CO2 will approach to be stable with the increase of the action time.The research results can provide a theoretical guidance for evaluating the potential of CO2 geological storage in anthracite reservoirs.
AnthraciteSupercritical CO2Pore structureAction timeCO2 geological storageNuclear magnetic resonanceFractal dimension
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