破碎性煤层段钻井液安全密度窗口的确定与应用

破碎性煤层段钻进过程中井壁坍塌、掉块严重,常规模型计算所得的坍塌压力当量密度难以较好地支撑煤层段井壁。依据破碎性煤岩的特征,系统分析了破碎性煤层段井壁失稳的机理,重新界定了破碎性煤层段的钻井液安全密度窗口。计算结果表明进入破碎性煤层段后钻井液安全密度窗口明显变窄。利用该模型对D2井三开破碎性煤层段的钻井液安全密度窗口进行了预测,理论计算结果和实钻情况基本吻合,验证了模型的合理性。研究成果对类似井段的井壁稳定性研究有借鉴意义。

A method to determine the density window for safe drilling of broken coal seam and its application

In the process of drilling in broken coal seam, wall collapse is serious. Application effects of collapse density obtained from the conventional model are generally not good. This article, based on the characteristics of broken coal seam, systematically analyzes mechanisms of wellbore instability of broken coal seam, and newly defines the density window for safe drilling of broken coal seam. The calculating results show that the density window for safe drilling start to narrow as the drilling bit penetrates into the broken coal seam. The model is carried out to predict the density window for safe drilling in D2 well, the calculation results are basically consistent with the actual conditions, showing that the method is reasonable and practical. The research results has certain reference for the analysis of wellbore stability in similar formation.