Mineral corrosion/precipitation characteristics and regularities during CO2 sequestration in shale
Supercritical CO2(scCO2)reaction may lead to dynamic changes in the material composition,accumulation and seepage condi-tions of shale.However,there are few reports on the water-rock reaction characterized by corrosion/precipitation and its influence regu-larities.Based on the use of high-pressure hydrothermal reaction experimental device and a series of characterization tests,the paper an-alyzes the changes of shale in chemical composition,mineral composition,surface morphology and pore structure during scCO2-water-shale reaction,revealing the regularities of mineral corrosion,ion dissolution and precipitation in shale under CO2 sequestration condi-tions.The results show that in the short-term reaction process,shale primarily exhibits corrosion characteristics,with changes in the internal calcite morphology and the development of secondary corrosion pores.In the long-term reaction process,corrosion is still domi-nant in shale,accompanied with occasional carbonate precipitation in partial areas.The corrosion process is mainly controlled by the de-velopment conditions of calcite,and calcite corrosion leads to an increase in the pore volume and specific surface area of shale.The pre-cipitation process is affected by clay minerals represented by illite and illite/smectite mixed layers,and an increase in both contents can lead to the formation of more carbonate precipitates.In general,scCO2-water-shale reaction exhibits a geochemical behavior that predomina-ted by corrosion and supplemented by precipitation.Under the effect of corrosion or precipitation,the sequestration space in shale presents a positive incremental evolution.The calcite corrosion helps improve hydrocarbon sequestration capability in shale.Clay minerals can provide essential cations for CO2 mineralization.The investigation on the corrosion/precipitation characteristics of shale during CO2 sequestration can help understand the geochemical regularities of minerals and fluids under CO2 sequestration conditions,which is of great reference value for revealing the CO2 geo-sequestration mechanism of shale and developing the enhanced shale gas recovery techniques.
shale gas reservoirCO2 geo-sequestrationscCO2-water-shale reactionmineral compositioncorrosion/precipitation characteristics
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