低渗透油藏CO2驱采油井试井模型

摘要

CO2 flooding has become an attractive enhanced oil recovery method in the world,however due to the fracturing and viscosity improvement,the characteristics of production well pressure responses become very complex.In practices,the pressure responses of CO2 flooding in low permeability reservoir often show the composite reservoir characteristics.However,the impact of the improvement of mixing fluid flow ability caused by CO2 dissolution and channeling are not clear.This paper provides a well test model for CO2 flooding production well in low permeability reservoirs based on profile equalization technology.The dimensionless bottom hole pressure is obtained by using the Laplace integral transform,and then the log-log well test curves are obtained by numerical inversion.The results show that composite pressure response of CO2 flooding production well are resulted from fracturing or acidification,rather than CO2 dissolution near the wellbore.On this basis,the proposed method can quantify the near wellbore permeability of production wells quickly and accurately for CO2 flooding.%低渗透油藏CO2驱油过程中,采油井的实测压力-压力导数双对数曲线往往后期上翘,采油井的试井压力响应同时受储层渗流能力和流体流动能力改变的影响,但人工压裂形成的物性分区和CO2溶解导致的黏度分区特征在其中的影响程度尚不明确.文中采用剖面均化方法建立了低渗透油藏CO2驱采油井试井数学模型,利用Laplace积分变换,求得无因次井底压力解,并通过数值反演获得双对数试井特征曲线.结果显示,低渗透油藏近井渗流介质改造作用是压力双对数曲线出现复合油藏特征的直接原因,而CO2窜流导致的混合流体流动能力改善并不是导致复合油藏特征的主要原因.在此基础上,采用混合流体黏度修正方法能够快速、准确地量化CO2驱过程中采油井近井渗流能力的变化.