3D Wellbore stability analysis in fractured formations: a seismic data-driven approach for safe mud weight window estimation in the Tarim Basin, China

Abstract

Accurate estimation of the safe mud weight window (MWW) is essential for ensuring drilling safety, reducing costs, and improving operational efficiency. In complex ultra-deep geological environments, fractures significantly narrow the MWW, posing challenges to drilling operations. Current wellbore stability analyses considering fractures are typically limited to 1D models. This study presents a novel efficient 3D curvature attribute integrated mechanical earth model (C-MEM) workflow driven by seismic data, designed for 3D wellbore stability analysis in fractured formations. The workflow begins by extracting fracture development probability from seismic data and determining fracture dip and strike through geometric structure transformation to provide 3D weak plane parameters. The C-MEM is then used to model the 3D in situ stress field, which is used for wellbore stress calculations. Additionally, traditional 3D models for pore pressure, collapse pressure, breakdown pressure, and leak-off pressure gradients are computed, as well as slip failure pressure and tensile failure pressure gradient models that account for 3D fractures. In the Tarim Basin of China, a high-precision C-MEM covering 600 km2 and reaching depths of up to 8000 meters was established, and blind well tests demonstrated the model’s accuracy to be 93.79%. The resulting 3D MWW model revealed that fractures significantly narrow the safe drilling window, and accurately predicted wellbore collapse events. The model successfully guided 22 drilling estimations in the Bozi block of China’s Tarim Basin, demonstrating its practical feasibility. This workflow enables pre-drilling prediction of wellbore instability events in fractured formations, transitioning from 1D logging data to a comprehensive 3D model.