基于漏失机理的碳酸盐岩地层漏失压力模型

漏失压力预测是防漏堵漏的关键。在孔隙型或含微裂缝的砂、泥岩地层中，依据破裂压力设计钻井液安全密度上限值是比较合理的，然而在缝洞发育的碳酸盐岩地层中，往往使得钻井液设计密度值偏大。为了保障安全顺利钻井，亟需建立碳酸盐岩地层的漏失压力预测理论。基于对碳酸盐岩地层钻井液漏失机理的新认识，建立了压裂性漏失、裂缝扩展性漏失、大型裂缝溶洞性漏失的漏失压力模型。压裂性漏失主要抵抗地应力，漏失压力近似等于地层破裂压力；裂缝扩展性漏失需要抵抗地应力和地层压力，漏失压力一般小于地层破裂压力；大型裂缝溶洞性漏失只需抵抗地层压力，漏失压力一般略大于地层压力。实例分析表明，漏失压力模型科学依据更加充分，也更具针对性，预测结果与实际情况比较吻合，为合理的钻井液密度设计及防漏堵漏提供了依据。因此，建议将漏失压力纳入到钻井工程设计中。

The lost circulation pressure of carbonate formations on the basis of leakage mechanisms

The prediction of lost circulation pressure is a key to leak resistance and sealing.It is reasonable for sandstone or mudstone formations with small pores or microcracks to design the upper safe density limit of drilling fluids based on fracture pressure,which,however,often results in a higher safe density value of drilling fluids for carbonate formations with developed fractures or caverns.Therefore,it is necessary to establish a theoretic foundation for the prediction of lost circulation pressure in order...