基于可靠性方法的储层钻井坍塌压力分析

A collapse pressure analysis in reservoir drilling based on the reliability method

结合可靠性方法及Hoek-Brown准则,推导出了煤层钻井坍塌压力的可靠度计算公式,选取了控制煤层井壁坍塌的随机变量,并采用室内实验方法确定随机变量的Weibull分布类型。以沁水盆地ZP-01井为例,分析了坍塌压力可靠度结果与Hoek-Brown准则定值法结果和Mohr-Coulomb准则定值法结果的差别,讨论了坍塌压力可靠度结果与随机变量个数及变异系数的关系。结果表明,ZP-01井坍塌压力的可靠度结果分别较Hoek-Brown准则定值法结果和Mohr-Coulomb准则定值法结果提高2.77%和4.82%;可靠度结果与随机变量变异系数呈非线性正相关关系;随机变量个数减少,可靠度预测结果略有减小。定值法相对偏小的坍塌压力预测结果使得ZP-01井551.45～552 m煤层段发生井壁坍塌,而可靠度预测结果大于定值法,这表明可靠度方法可以进一步提高煤层坍塌压力的预测精度。

Integrated with a reliability method and the Hoek-Brown criterion,we deduced a reliability calculation formula for collapse pressure in coal seam drilling.Random variables dominating collapse pressure in coal seam drilling were selected and the corresponding Weibull distribution type of these variables was determined with indoor experiment methods.Taking a coal seam from Well ZP-01 in the Qinshui Basin as an example,we compared differences between the reliability result of collapse pressure and that derived from the value analysis method according to the Hoek-Brown and Mohr-Coulomb criteria,and discussed the correlation between the reliability result of collapse pressure and the number of random variables as well as the variation coefficient.The result shows that the reliability result of collapse pressure in Well ZP-01 is 2.77% and 4.82% higher than that derived from the value analysis method according to the Hoek-Brown and Mohr-Coulomb criteria,respectively.There exists a nonlinear positive correlation between the reliability result and the variation coefficient of random variables,and the reliability prediction result decreases slightly with decreasing the number of random variables.A relatively smaller prediction result of collapse pressure derived from the value analysis method resulted in the collapse of coal seam at depth from 551.45 m to 552 m in Well ZP-01,while the reliability prediction result of collapse pressure greater than that derived from the value analysis method implied that the proposed reliability method of collapse pressure could further improve the prediction accuracy of collapse pressure in coal seam drilling.