Successful Deployment of a High Solids Laden Divalent Brine-Based Drill-In Fluid in a Deep-Water Offshore Brazil Operation

This paper surveys successful field trial application and results of a divalent brine-based drill-in fluid (DIF) designed for deep water operations in Brazil. The operations took place in a pre-salt reservoir section of the Santos Basin where the reservoirs are well known for their high hydrocarbon pressures. Several factors were taken in account when designing the successful fluid such as densities, rheology, fluid loss control, lubricity, fluid invasion, environmental regulations, true crystallization temperature, pressurized crystallization temperature, and compatibility with native fluids. The successful DIF focused on minimizing environmental footprints and fluid loss control. The fluid was developed to cover a density range of 12.9 and 13.5 lbm/gal and withstand temperatures >212°F. Approximately 120 – 164 lbm/bbl of marble calcium carbonate package was used to laden the fluid. The carbonate package also provided filtration control, sealing 20-, 55-, and 120-μm pore throat allowing low spurt loss, low filtration volumes, and minimal filter cake thickness. Fluid rheology was monitored from liquid mud plant mixing to rig site application. Minor pH-buffering treatment was required while drilling. By closely controlling the fluid properties in the optimal window, the equivalent circulating density (ECD) was maintained per plan. The fluid stability allowed for 12 days of logging operation without phase separation and/or sagging issues. A core of 39.8 meters was cut without presenting any issues. During the drilling operations, a high downhole fluid loss rate was identified. It was effectively controlled with the planned lost circulation material using the DIF as a based fluid. Fluid was stable for over 35 days with excellent recovery rate. Minimal product additions and a low quantity of fresh DIF volume required to maintain volume and properties. This paper also details results of six wells drilled during the field trials, and the experience which allowed the drilling of more than 2000 meters of reservoir using the divalent DIF.