Research on Dynamic Wellbore Stability Based on Wellbore Seepage

Due to the mutual flow between drilling mud and formation fluid, the pore pressure in the surrounding rock of the wellbore directly affects the rock’s mechanical properties. Since the properties and density of drilling mud are adjusted in real time during drilling operations, wellbore stability is inherently a dynamic process. This study aims to enhance wellbore integrity and reduce drilling accidents by investigating the dynamic characteristics of wellbore stability.

Rock mechanics experiments were conducted to simulate the mechanical properties of rocks under varying pore pressure conditions, yielding the quantitative relationship between pore pressure and rock mechanical behaviors. In conjunction with the radial seepage characteristics around the wellbore at different drilling stages, dynamic fluid-solid coupling simulations of the wellbore were performed based on geomechanical principles, enabling the development of a dynamic wellbore stability prediction method. This method further facilitates the prediction of key parameters such as wellbore collapse period and radial collapse depth.

This dynamic wellbore stability prediction technology was applied to three wells drilled in sandstone formations. It successfully predicted the collapse depth and period under different drilling mud densities and properties, significantly improving drilling efficiency while ensuring wellbore integrity. Compared with static wellbore stability prediction techniques, this technology provides drilling engineers with a richer set of drilling parameters and defines a clear wellbore collapse period, thereby effectively preventing stuck pipe accidents. Comparative drilling tests in the same block and formation layer showed that drilling efficiency increased by 12%, and the stuck pipe accident rate decreased by 27.3%.

This exploratory research demonstrates that wellbore stability in permeable formations during drilling is indeed a dynamic equilibrium process. As drilling mud properties, time, and stress conditions change, wellbore stability evolves accordingly. Predicting dynamic parameters can provide valuable references for drilling design and optimization, thereby enhancing wellbore integrity and minimizing drilling accidents.