缝洞型碳酸盐岩地层井漏预测的模糊数学方法

A fuzzy method for predicting the lost circulation of fractured / caved carbonate formations

井漏是深井超深井钻井工程中最普遍的复杂性事件之一。基于碎屑岩层系欠压实理论的压力预测等方法不适用于碳酸盐岩层系,使得碳酸盐岩储层钻前井漏预测难度加大。运用模糊数学理论,将井漏中地质因素中的各影响因素及其对漏失通道判断较敏感的地震属性等进行分层,建立漏失概率评价数学模型;应用工程模糊数学的指标隶属度刻画方法,建立易量化指标的隶属度函数,进而用九标度法和均方根法计算及分配高、低层次指标的权重,采用加权合成得到评价值,综合评判待钻地层漏失概率。经检验,所建立的漏失预测模型预测值与实际符合程度较高,表明该预测方法具有一定的可行性。

Lost circulation is one of the most common and complicated downhole accidents in deep and ultra-deep drilling operations.Besides,pressure prediction methods based on the undercompaction theory of clasolites are inapplicable to carbonate formations,resulting in more difficulties in predicting lost circulation prior to drilling in carbonate reservoirs.Therefore,by classifying various geological factors causing lost circulation and seismic attributes sensitive to porous media,we established a mathematical model to evaluate the probability of lost circulation,and through the membership depicting method in the fuzzy theory,we created the membership function for quantitative results,and adopted nine-scale method and mean square root method to calculate and distribute the weight of higher and lower indexes.Evaluation results were finally worked out through the synthetic weighted method for a comprehensive evaluation of the leakage probability of the target zone.The prediction results of the model were validated to be highly consistent with actual values,proving that this prediction method is fairly feasible.