高压窄密度窗口油基钻井液固井技术

海上油田固井作业面临着高压窄密度窗口易发生漏失和气窜，油基钻井液环境下固井井壁滤饼清洗困难，大斜度定向井固井顶替效率低等诸多挑战。在分析相关固井技术难点的基础上，采用高密度冲洗液提高对油基钻井液套管壁及井壁滤饼的清洗质量；选用聚合物增强水泥浆体系，在固井压耗动态计算及压稳计算的基础上优化双凝水泥浆柱设计，实现防漏及压稳储层；采用旋转尾管固井技术实现固井过程中尾管旋转，提高冲洗液的洗井质量及水泥浆顶替效率。上述技术措施在涠洲油田压力系数高达1.61 g/cm3、高气油比达358 m3/m3、密度窗口仅0.12 g/cm3 的油基钻井液固井施工中成功应用，固井质量评价优良，表明该套海上油田固井技术能够满足高压窄密度窗口油基钻井液的固井需求。

Cementing technology in the environment of oil based drilling fluid with high-pressure narrow-density window

The cementing operation in offshore oil fields is faced with many challenges. For example, circulation loss and gas channeling tend to happen at high-pressure narrow-density windows. When oil based drilling fluid is used, the filter cakes on the cementing wall can’t be removed easily. And the cementing displacement efficiency of highly-deviated directional wells is low. There are some technical measures to solve these problems. First, high-density flushing fluid was adopted to improve the cleaning quality of filter cakes on casing walls and borehole walls in the environment of oil based drilling fluid, after the technical difficulties related with well cementation were analyzed. Second, the polymer reinforced slurry system was adopted and bi-setting slurry column design was optimized based on the dynamic cementing pressure loss calculation and the pressure stability calculation, so that the circulation loss was prevented and the pressure stability of reservoir was realized. And third, the rotating liner cementing technology was adopted to rotate the liner in the process of well cementation so as to improve the cleanout quality of flushing fluid and the displacement efficiency of cement slurry. These technical measures were successfully applied in Weizhou Oil Field for the cementing operation of oil based drilling fluid with high pressure coefficient (1.61 g/cm3), high gas/oil ratio (358 m3/m3) and narrow density window (0.12 g/cm3). And the cementing quality was evaluated as good level.