Engineering practice of CO2 ESGR in Nanchuan normal-pressure marine shale gas reservoirs
Current experimental researches and simulation have demonstrated the theoretical feasibility of CO2 flooding to enhance shale gas recovery,but its actual engineering effects have not been verified in field tests.Based on the geological occurrence and production behaviors of Nanchuan normal-pressure shale gas reservoir in the Sichuan Basin,this paper studies the mechanisms of shale isothermal adsorption and CO2-CH4 competitive adsorption,carries out the first field test of CO2 huff and puff in a normal-pressure marine shale gas attenuation well,and points out the research direction of establishing a set of technological system.And the following research results are obtained.First,in the late production period,a gas well enters the stage of low pressure and low production,presenting the characteristics of insufficient formation energy,so it is an important stage to improve the degree of reserve recovery of the well.Second,compared with low-pressure and high-pressure shale,normal-pressure shale is much higher in CH4 and CO2 adsorption capacity,so CO2 ESGR is feasible and necessary.Third,shale samples of normal,high and low pressure adsorb more CO2 than CH4 under the same conditions,and their gas adsorption capacities are ranked as Nanchuan(normal pressure)marine shale＞Changning(high pressure)marine shale＞Yanchang(low pressure)continental shale.Fourth,CO2 huff and puff shows a remarkable stimulation effect in the test well,with an increase of single-well estimated ultimate shale gas reserves(EUR)from 0.75×108 m3 to 0.90×108 m3,single-well controlled reserves of 5.186×108 m3 and a recovery factor increase by 2.9%.In conclusion,breakthrough progress has been made for the first time in the CO2 huff and puff test of a normal-pressure marine shale gas attenuation well in China,which provides important guidance and reference for the research&development and application of ESGR technologies for shale gas wells in China.What's more,it is in an urgent need to conduct the resource potential and timing evaluation of CO2 ESGR in shale gas attenuation wells and the quantitative effect evaluation and technological optimization of CO2 ESGR,and establish a complete set of key technologies and standard systems of CO2 ESGR for shale gas attenuation wells.
Sichuan BasinNanchuan normal-pressure marine shale gasAttenuation wellProduction behaviorCO2 huff and puffEnhanced shale gas recovery(ESGR)Displacement and replacementCarbon sequestration
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