一种准确预测钻井液安全密度窗口的新方法

New accurate prediction method of safe window of drilling fluid density

史亚红 夏宏泉 彭梦 陈宇 陈颖杰2

西南石油大学油气藏地质及开发工程国家重点实验室，四川 成都 610500 中国石油西南油气田分公司工程技术研究院，四川 成都 610000）

State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu 610500, China Engineering Technology Research Institute, Southwest Oil and Gas Field Company, PetroChina, Chengdu 610000, China

准确预测钻井液安全密度窗口是井身结构设计和钻井液密度合理选择的前提。常用的钻井液安全密度窗口预测方法是基于Mohr￣Coulomb破坏准则和拉伸破坏准则而建立的。但是，由于Mohr￣Coulomb破坏准则未考虑中间主应力的影响，预测的钻井液密度偏高，不利于钻井提速和储层保护。为此，引入Mogi￣Coulomb破坏准则，建立了3种地应力状态下预测直井钻井液安全密度窗口的新方法，克服了传统方法计算坍塌压力过于保守和计算破裂压力未考虑剪性破裂的不足。将其应用于川西地区H1井砂泥岩地层的钻井液安全密度窗口计算中，结果表明，新方法的预测结果较传统方法的计算结果更符合实际情况，且精度高、实用性强，对解决钻井中的井壁失稳问题有重要的指导意义。

Accurately predicting the safe window of drilling fluid density is a prerequisite for well structure design and reasonable choice of drilling fluid density. The commonly used prediction method is based on Mohr?鄄Coulomb failure criterion and tensile failure criterion. However, the Mohr?鄄Coulomb failure criterion does not consider the role of intermediate principal stress, which makes the predicted drilling fluid density too high, and then greatly affects drilling speed and reservoir protection. Therefore, the Mogi?鄄Coulomb failure criterion is introduced and a new method to predict the vertical safe window of drilling fluid density is established under three stress states. This method overcomes the shortcomings of the traditional model that calculation of collapse pressure is too conservative and calculation of fracture pressure does not take into account shear failure. It is used to calculate safe window of drilling fluid density of the sandstone and mudstone formation for H1 Well in western Sichuan. It is found that the prediction is more practical and accurate than traditional method. The results show that the result predicted by the new method is more realistic than those calculated by traditional method and has high precision and practicability. These results have important guiding significance to solve the instability of borehole during drilling.

10.6056/dkyqt201902024