天然裂缝性地层漏失压力预测新模型

A NEW LEAKAGE PRESSURE PREDICTION MODEL FOR NATURAL FRACTURED FORMATION

漏失压力是地层漏失性质中的一个重要参数,合理确定漏失压力是提高地层防漏堵漏成功率的关键。目前裂缝性漏失压力模型存在缺乏理论依据、施工作业可操作性差等问题。为了准确预测裂缝性地层的漏失压力,为钻井施工提供有力指导,文章在分析裂缝性漏失机理的基础上,从井壁围岩应力状态出发,选择破裂准则,创新地建立了基于裂缝与井筒相交环面应力状态的漏失压力新模型,并以渤中34-9区块5口探井的漏失点为实例对该模型进行了验证。结果表明,5口探井漏失点处的实际井底压力均大于新模型求得的漏失压力,新模型的计算结果与现场实际情况比较吻合。该模型可为天然裂缝性地层钻井液密度的优化设计提供理论依据,能够有效地指导现场钻井作业的安全施工。

Leakage pressure is an important parameter for thief zones.It is key for loss prevention and control.The existing leakage pressure models for fractured formation lack theoretical basis and have low applicability at site.For an accurate prediction for a better guide on drilling operations,on basis of the loss mechanism of fractured formation,and starting from the stress condition on the rocks surrounding the bore hole,an innovative leakage pressure model is set up.It is verified by the 5 exploratory well cases at Bozhong 34-9 block.The results show the actual bottom hole pressure at the loss point is greater than leakage pressure calculated by new model,so the new model matches the actual operations.This new model can provide theoretical foundation for drilling fluid density optimization and guide the safe operation in fractured formations efficiently.