绕流在层流固井中的危害与防治

在层流固井中,水泥浆容易绕过前面的钻井液和井壁黏稠的钻井液,而发生绕流现象。这种现象容易引起水泥浆与钻井液混浆,从而造成环空水泥环胶结不良。尽管人们在预防绕流的机理研究方面做了大量的工作,但至今仍未对注水泥顶替的优化设计方法形成统一的认识。通过室内的绕流实验研究和大量的现场固井实践,发现套管的"重点扶正"、水泥浆柱的"负密度梯度结构"、冲洗液的"高效降黏"、隔离液的"强力牵引"和水泥浆的"稠浆慢替"是减少绕流、提高层流顶替效率的有效措施。应用上述固井措施,南海海域十多口井的固井作业均取得了成功,固井质量达到了优良水平。

Harm of bypassing flow in laminar flow well cementation and its prevention and cure

Bypassing flow is apt to happen when the cement milk bypasses the thick drilling fluid on the in the process of laminar flow cementation.This phenomenon will cause the mixture of cement milk and drill fluid which results in the weak bond of cement mantle.There is not a universal idea of optimization design method of cementing displacement though a lot of work has been done for bypassing flow prevention.Through the bypassing flow experiments in house and quantities of field well cementation practice,it was found "priority centering" of casing,"negative density gradient structure" of cement milk,"high efficiency viscosity break" of circulation fluid,"intensive draw" of isolation fluid and "thick displacement slow" of cement milk,all these were effective measures to decrease bypassing flow and improve the displacement efficiency.Cement jobs of more than 10 wells in South China Sea zone were all big success and the cement quality came to fineness level.