Wellbore collapse model of fractured formation considering drilling fluid plugging effect
LU Yunhu1，2，ZHANG Yingxi2，JIN Yan1，2，ZHOU Bo2，3
(1. State Key Laboratory of Petroleum Resources and Prospecting，China University of Petroleum(Beijing)，China University of Petroleum(Beijing)，Beijing 102249，China；2. College of Petroleum Engineering，China University of Petroleum(Beijing)，Beijing 102249，China；3. PetroChina Tarim Oilfield Company，Korla，Xinjiang 841000，China)
Abstract：Currently，wellbore instability in fractured formations significantly impacts the exploration and development of ultra-deep oil and gas resources. Traditional analytical models for wellbore stability struggle to account for the effects of drilling fluid plugging，and the computational efficiency of numerical simulation methods often fails to meet the demands of efficient drilling. To address these issues，a wellbore collapse mechanical model for fractured formations that incorporates the drilling fluid plugging effect has been established based on the mechanics of discontinuous media. Additionally，a method to verify the model?s computational results using the effective stress between fractured blocks has been proposed. The study analyzes the influences of drilling fluid plugging，block fragmentation degree，mechanical parameters，in-situ stress，hole size，and other factors on collapsing pressure. The results indicate that wellbore instability in fractured formations is primarily caused by shear slip of fractured blocks，which arises from unbalanced forces between these blocks. Unlike traditional theories，this study reveals that wellbore instability can also result from excessive drilling fluid density，and the direction of collapse may vary accordingly. Furthermore，the plugging effect of drilling fluid is positively correlated with wellbore stability，while the degree of block fragmentation is negatively correlated with it. Field verification demonstrates a significant improvement in wellbore stability following the application of drilling fluid density and plugging performance designed according to the new model. This research provides theoretical support for selecting appropriate anti-collapse drilling fluid densities and plugging performance in well drilling within fractured formations.
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2025, Vol. 44 
