地层水侵入对超临界CO_2钻井井筒温度和压力的影响

Influences of formation water invasion on the well bore temperature and pressure in supercritical CO_2 drilling

为了研究SC-CO2(超临界CO2)连续油管钻井过程中地层水侵入对井筒温度和压力的影响,在综合考虑CO2流体的黏度、密度、导热系数、热容、焦耳-汤姆逊系数等参数影响的基础上,建立了SC-CO2连续油管钻井地层水侵入井筒流动模型,并采用各参数相互耦合的方法对井筒温度和压力分布进行了计算。结果表明,地层水侵入速度越大其混合流体密度越高,环空混合流体对流换热系数越大,但由于喷嘴节流产生的焦耳-汤姆逊冷却效应,在井深约1 900 m处(离井底约10 m处)环空混合流体密度突然增大、对流换热系数突然减小;同时井筒流体温度随地层水侵入速度的增加而升高,在井深约1 900 m处焦耳-汤姆逊冷却效应导致井筒流体温度急剧降低;此外,井筒环空压力也随着地层水侵入量的增加而增大,但增幅不明显。

Aiming to study the influence of formation water invasion on the well bore temperature and pressure in SC-CO2（supercritical CO2） drilling with coiled tubing,this paper builds up a wellbore flow model with formation water invasion in SC-CO2 drilling with coiled tubing,based on the comprehensive investigation of the influence of viscosity,density,thermal conductivity,isobaric heat capacity and Joule-Thompson coefficient of SC-CO2.The wellbore temperature and pressure distribution were calculated by the method of coupling among these parameters.The results show that the bigger the rate of invaded formation water and the bigger the density of mixed fluid,the bigger the convective heat transfer coefficient in the annulus.Because of the Joule-Thompson cooling effect caused by nozzle throttling,the annulus mixture fluid density increased abruptly and the convective heat transfer coefficient decreased abruptly at the well depth of about 1 900 m（about 10 m to bottom hole）.Meanwhile the wellbore fluid temperature increased with the invasion rate of formation water,and the same Joule-Thompson cooling effect caused the wellbore fluid temperature to decrease abruptly at the well depth of about 1 900 m.Moreover,the wellbore annulus pressure increased with the increasing of invaded formation water quantity,but the amplitude is not obvious.