Dual Gradient Mud Cap Technique and Monitoring System Developed to Manage Total Losses While Drilling in the Brazilian Pre-Salt Carbonate

Abstract The standard float mud cap drilling (FMCD) was adapted to the dual gradient mud cap drilling (DGMCD), a fit-for-purpose contingency technique for drilling under the potential of total fluid loss scenario in the Brazilian pre-salt carbonates, which can present vugs and natural fractures. The primary barrier is still the hydrostatic column, achieved by two different fluids in the annular space: a seawater cap and a heavy annular mud (HAM). While the HAM is constantly injected in the annulus to prevent gas migration, keeping the well dynamically dead while drilling, the sacrificial fluid (SAC) is pumped down the drill string to carry the rock cuttings into the fractures/vugs. In order to enhance the process safety controls for the execution of this technique in a Brazilian pre-salt well, a DGMCD real-time monitoring system was developed. The system relies on monitoring the drilling parameters and is significantly enhanced by feeding them to a real-time hydraulic simulator to provide process safety and operational problems alarms/diagnostics. This specific early detection tool, developed in a drilling smart twin, allows the operator to either prevent or mitigate any unwanted event and to rapidly respond to avoid escalation. Based on cause and effect algorithms, high-speed data processing, and human knowledge, the solution is capable of automatically identifying caves/vugs, fractures plugging, kick/gas migration and pack offs while drilling in total losses scenario. Besides that, based on downhole data and hydraulic simulation, the technology also provides a well schematic illustration that updates in real time the interface between the two fluids in the annular space. The technology was used in combination with theoretical and simulator training for the onsite/offshore team to deliver personnel competence and reliable human response to manage the technique execution. The monitoring system enabled a quality environment to support the human decision-making process in real time during operations while enhancing the level of the process safety controls in place for drilling a wildcat well. The methodology was conceived for the use in a Brazilian pre-salt well recently drilled in an ultra-deepwater location. The real-time simulation-based monitoring system presented in this article is a further step to ensure the reliability of mud cap drilling (MCD) operations in challenging scenarios where total losses are faced while drilling, aiming for an increase in efficiency and safety.