Implementation of MPD Systems in the Deepwater Gulf of Mexico to Drill Highly Depleted Reservoir Sections

Abstract

Abstract Combined challenges of drilling deep water matured reservoir hole sections with high levels of depletion present a risk for major downhole fluid loss events, well control hazards, and the resulting high remedial cost. Reduced fracture gradient, due to depletion and near-wellbore thermal stress, combined with potential near-virgin sands results in narrow-drilling margins impacting the probability of success drilling to planned depth and meeting objectives of the well. In some can cases the narrow-drilling margins can even make these reservoirs un-drillable without alternative technologies. Constant Bottom Hole Pressure (CBHP) variant of Managed Pressure Drilling (MPD) was identified as an enabling technology to help mitigate the risk of drilling the reservoir through the presence of highly pressure depleted sands and wellbore cooling risk mixed with virgin pressure stringers within the same interval. MPD systems were installed on two drill ships, and four (4) deepwater wells were successfully drilled through highly depleted reservoirs using MPD. MPD enabled the downhole pressure to be reduced by using a mud weight that was hydrostatically underbalanced to the pore pressure and use surface back pressure (SBP) to maintain overbalanced to the virgin reservoir conditions during static conditions. The effect of the equivalent circulating density (ECD) due to the friction while circulating (dynamic conditions) was offset by reducing the surface back pressure and maintain a near constant bottom hole pressure at a selected depth. The MPD system also allowed the application of dynamic pore pressure verification, to reduce the uncertainty in the drilling window. At TD the drilling bottom hole assembly (BHA) was pulled while maintaining the MPD condition. Production liner was then run in MPD mode and cemented using Managed pressure cementing techniques. This paper describes the process for the selection and implementation of MPD systems on two drill ships; it highlights the process for permitting the operations and the preparation of the rig crews to apply new developed procedures. Furthermore, the paper describes the results obtained after successfully executing the MPD drilling operations.