深水钻井井壁稳定性评估技术及其应用

Evaluation and application of wellbore stability in deep water

蔚宝华 闫传梁 邓金根 刘书杰 谭强 肖坤

YU Baohua YAN Chuanliang DENG Jin LIU Shujie TAN Qiang XIAO Kun

中国石油大学，北京　102249 中海石油研究总院，北京　100027

China University of Petroleum, Beijing 102249, China Research Institute of China National Offshore Oil Corporation, Beijing 100027, China

深水地层上覆岩层压力低，井眼破裂压力低，安全钻井液密度窗口窄，易发生井壁失稳，因此，准确评估安全钻井液密度窗口对深水钻井十分必要。深水地层井壁稳定性研究难点在于准确评估上覆岩层压力与建立浅层井眼坍塌压力和破裂压力计算模型，针对国外现有模型中对深水地层密度评估存在偏差的问题，从深水地层特性出发，认为深水浅层和深层处于不同的成岩阶段，应采用不同的模型进行密度评估；针对深、浅层井周应力状态的差异，分别对深水浅层和深水深层的井壁稳定性进行研究，得出了安全钻井液密度窗口计算的分段模型。利用该模型对南海某深水气田的安全钻井液密度窗口进行了评估，评估结果与实钻情况吻合，表明该模型准确、可靠，为深水钻井液密度设计提供了重要依据。

The deep water formation has low overburden pressure, low fracture pressure and narrow safety window of mud density. So the risk of wellbore instability is very high in this kind of formation. It is significantly important to accurately evaluate the safety window of mud density. The difficulties of wellbore stability analysis in deep water are how to accurately predicate the overburden pressure and establish the calculation model of caving and fracture pressure in the shallow part of the deep water formation. The published foreign models, for calculating the overburden pressure in the shallow part of the deep water formation, have precision problems in density evaluation. In this paper, we begin from the properties of deepwater formation, and suggest that different models should be used according to the different diagenetic stages in the shallow and deep part of the deep water formation.The wellbore stability is researched for shallow and deep parts separately, and different models are obtained. The model is used to evaluate the safety window of mud density in a deep water gas field in South China Sea. The result is coincide with the really drilling condition, which indicates the model is accurate and reliable and can supply useful information for mud density design in deep water drilling.