The deepwater development field in the western Gulf of Mexico (GoM) presents an array of complex challenges for ultra-deepwater drilling operations. The four well campaign was particularly challenging due to extreme water depths, remote location, well trajectory and a narrow pressure environment, 350-100 kpa (50-150 psi), for extended reservoir laterals. The authors highlight the use of innovative technology employed to drill and complete wells in the western GoM deployment, coupled with the first-ever use of controlled mud level (CML), managed pressure drilling technology in the Gulf of Mexico. The approach of selecting the fluid systems to achieve the objectives and the use of hydraulics modeling software with CML modeling capability in the design, planning and execution phases of the project allowed for fluid design optimization. The results were a successful drilling and completion campaign managing multiple fluids systems and operations on an ultra-deepwater, dual-activity drill ship in water depths more than 8,500 ft (2,591 m). The authors discuss the initial use of a low equivalent circulating density (ECD), flat-rheology synthetic based fluid (SBF) designed for narrow margin drilling applications and the transition to the deployment of a newly developed high-performance water-based mud (HPWBM) optimizing the operations to drill the intermediate intervals for final two wells. The authors also will discuss use of the reservoir drill-in fluid (RDF) and solids-free screen running fluids (SF-SRF), designed specifically for use in these open holes, gravel pack completions at hole angles upwards of 90°. Operational efficiencies derived from use of these fluids include ECD management, hole cleaning, directional performance, reduction in downhole losses, and the elimination of non-productive time (NPT) in a narrow margin environment with no loss of rate of penetration (ROP). Additional efficiencies include the seamless transition from derived from use of water-based fluids for drilling and completion phases. Use of the CML technology allowed for precise control of the hydrostatic pressure on wells that previously would not have been technically feasible to drill or complete. The novel use of the newly developed HPWBM on this campaign enabled reduced health, safety and environmental (HSE) exposure impact, increased tank and rig cleaning efficiency, and the elimination of a wellbore cleanout run since the entire well was drilled with only water-based fluids. The fluids were successfully employed in the four wells drilled and completed in a managed pressure environment utilizing CML technology.

Effective hydraulic modeling to predict the equivalent circulating density (ECD) was highly critical for successful drilling of a pilot well in a deepwater development in the Gulf of Mexico. The drilling objectives included linking three reservoirs, divided by moderately thick shale at relatively high dip while upholding the properties between relatively narrow drilling margins. This difficult drilling environment mandated intensive reservoir drill-in fluid maintenance practices with specific focus on rheology, density, and optimization of bridging materials while reducing the incorporation of acid-insoluble solids.The pilot, Well B, is one of a handful of horizontals drilled in ultra deepwater shallow BML, having over 2,000 feet lateral, that was successfully drilled in challenging 8,257 feet of deepwater in the Paleogene reserve at a shallow depth of 2,300 feet TVD below the mudline (BML) and the first well to be produced in this reserve development. Due to the shallow depth from the mudline and soft sediments, the drilling margins were extremely low -0.7 lb/gal (i.e., 250 psi); thus wellbore stability analyses were critical in order to avoid unanticipated losses to formation, losses to mudline, influxes or borehole collapse. Despite the limitations of available offset data used as an analog, the pore pressure and geological fracture gradient were known. However, in comparison to offset Well A (3,800 ft BML) with pressure margins 450 psi, Well B realized a significantly reduced operating pressure window and shallower depth BML. The ECD, equivalent static density (ESD), downhole pressure, and flow rate were carefully monitored to enable drilling within the established operational window and increasing the success of attaining total depth. The meticulous monitoring was a key to the ability to successfully drill the lateral section with only marginal losses and no wellbore stability problems.The paper presents the hydraulic modeling in addition to the field monitoring data as well as summarize the lessons learned from pilot Well B as compared with offset Well A.