裂缝性致密储层钻井完井液漏失损害带模拟

Simulation of Damage Zone Due to Lost Circulation of Drill-in Fluid in Fractured Tight Reservoirs

裂缝性致密储层钻井完井时,钻井完井液固相及其滤液板易侵入储层,使近井地带渗透率下降,影响油气井产能。以九龙山构造珍珠冲组致密砾岩储层为研究对象,基于双重连续介质模型,建立了钻井完井液在裂缝网络中的径向溶质运移数学模型,通过有限差分法求解,确定了不同时间下距离井筒不同位置的钻井完井液无因次浓度分布剖面,定量评价了钻井完井液的漏失损害程度,并通过压力恢复试井解释以及钻井完井液动态损害评价实验对模拟结果进行了验证。模拟结果表明:钻井完井液的侵入深度随井漏时间的增加而增加;漏失损害带半径约为17 m,表皮系数为7.50,试井解释及室内实验结果同数值模拟结果的相对误差均小于10%,证明了模型的可靠性。

The invasion of drill-in fluid into reservoir formation can lead to a damage zone around the wellbore during the process of over balanced drilling and completion in fractured tight reservoirs,which will strongly affect the production performance of a well.Taking the tight conglomerate reservoir of Jiulongshan structure as the research object,the mathematical model of solute transport in fractured network was established by double continuous medium method;the dimensionless concentration at any time in different position from wellbore was determined by using finite difference method to solve the developed model;the extent of formation damage caused by drill-in fluid loss was quantitatively evaluated,and the numerical results were validated by pressure built-up test analysis and dynamic damage assessment of drill-in fluid.The numerical results show that the depth of drill-in fluid invasion increases over time,and pollutions induced by the drilling fluid loss continuously push and cumulate in depth of the formation with the kill fluid loss;respectively,the radius and equivalent skin factor of damage zone due to lost circulation of drill-in fluid is about 17.0 m and 7.5,the relative errors between the numerical results and the results of pressure built-up test analysis and dynamic damage assessment are less than 10%,which proves the reliability of the model.