Unraveling Mass-Transfer Effects on Gas Influx Behavior in Non-Aqueous Muds: Experimental Characterization of Well Control Dynamics Using Rheology-Matched WBM and SBM Systems at Full Scale

Abstract Modern MPD-based well control operations still face challenges with effective gas influx detection and management, including the application of appropriate kick detection thresholds across different mud systems and the limited understanding of mass transfer dynamics and multiphase behaviors when non-aqueous drilling fluids are involved. Through a comprehensive full-scale comparison of gas influx signatures between water-based mud (WBM) and Synthetic-oil-based Mud (SBM) systems with matched rheological properties, we aim to characterize the mass-transfer-dependent effects on gas influx behaviors. Experiments were conducted at LSU's PERTT Laboratory using a full-scale wellbore equipped with industry-standard Managed Pressure Drilling (MPD) systems and distributed fiber-optic sensing (DFOS) technology. A systematic rheological matching protocol was used to formulate WBM and SBM systems with near-identical flow behavior across temperature and pressure ranges relevant to drilling operations. This unprecedented rheological equivalence allowed us to isolate mass-transfer-dependent effects on gas influx behaviors. Controlled gas influxes were introduced under various operating conditions, with continuous monitoring of pressure, temperature, and flow parameters throughout the wellbore. Key multiphase phenomena, including gas slippage, dispersion behavior, and mass transfer between phases, were measured and analyzed. The experimental results revealed significant differences in gas influx signatures that challenge the industry practice of kick detection thresholds across different mud systems. The DFOS measurements demonstrated spatial and temporal resolution of gas influx signatures, showing that SBM systems, despite having similar rheological parameters, exhibited fundamentally different gas dissolution rates and bubble dynamics compared to WBM. The high-resolution data collected throughout the wellbore demonstrated that conventional models underestimate the complexity of gas-SBM interactions, particularly regarding gas dissolution and potential release and their time-dependent nature. An advanced transient multiphase flow simulator was used to compare predictions with our experimental observations, enabling the refinement of mass transfer submodels and slip correlations specific to each mud system. This improved modeling capability facilitates the development of enhanced early warning algorithms that account for the unique mass transfer characteristics. This research presents the first comprehensive full-scale experimental comparison between rheology-matched WBM and SBM systems, isolating the mass-transfer-dependent effects on gas influx behavior. The unique dataset from the full-scale facility with advanced MPD and sensing capabilities fills a knowledge gap in multiphase flow behavior in different drilling fluids, advancing both theoretical understanding and practical well control applications.