探井二开以下地层井壁稳定性钻前预测方法

Borehole stability prediction before drilling for formations under the second section in an exploration well

综合分析钻井过程中通常遇到的井漏、缩径和坍塌等复杂情况,确定已钻层段的坍塌压力和破裂压力,结合神经网络理论建立地震层速度与坍塌压力、破裂压力之间的非线性映射关系,提出利用地震资料钻前预测勘探构造第1口井二开以下地层井壁稳定性的方法。中国西北地区某油田钻探某构造的YS-D井二开层段钻进过程中出现泥岩垮塌,三开层段开钻前利用该方法对三开层段坍塌压力当量钻井液密度和破裂压力当量钻井液密度进行了预测,基于预测资料调整了钻井液密度,钻进基本正常。该方法自2001年4月以来已在52口探井中成功应用。应用效果表明利用该法预测的三开层段钻头下部300 m内地层的压力变化结果与实际钻井中得到的数据较为接近,达到了钻前预测井壁稳定性的要求。

Based on the comprehensive analysis of some complicated situations met in drilling, such as circulation loss, borehole shrinkage and collapse, the collapse pressure and fracture pressure of the drilled well interval were determined. And the nonlinear relationships between the seismic interval velocity, the collapse pressure and the fracture pressure were established by neural network theory. A new borehole stability prediction method was put forward, that is, predicting the collapse pressure and fracture pressure of the formation under the second section of the first exploration well in prospecting area using seismic data. Mudstone collapse happened when drilling the second section of well YS-D in a field, northwest China. Before drilling the third section, the equivalent drilling fluid density of the collapse pressure and that of the fracture pressure of the third section were predicted by this method, and the density of drilling fluid was adjusted and the drilling made good progress. The method has been successfully applied to 52 exploration wells since April, 2001. The predicted pressure change is close to the actual result within 300 m under the bit in the third section, meeting the demands of predicting borehole stability before drilling.