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.
This paper presents how a Controlled Mud Level (CML) Managed Pressure Drilling (MPD) system was used to place Horizontal Open Hole Gravel Packs (HzOHGP) in low Pore Pressure Frac Gradient (PPFG) margin reservoirs. This industry-first accomplishment took extensive preparation and precise on-site coordination between CML and gravel pack operations. In the target reservoirs, the margin between the pore and fracture pressures is too small to place gravel packs using conventional methods. CML was identified as an opportunity to resolve this problem. A primary design phase goal was to develop a deep understanding of the flow paths and fluid properties at every stage of the gravel pack operation. This information is critical to evaluating the frictional pressure drops effecting the pressure in the open hole. The team developed procedures that incorporated step rate tests and real-time downhole measurements to calibrate the friction models, which were then used to precisely control the CML during the pumping jobs. CML was able to limit the downhole treating pressures to stay within the low PPFG limits. The post-job analyses showed that total screen coverage was achieved for all the jobs in the campaign, demonstrating the project team's high level of coordination, cooperation, and cross-discipline understanding. While the industry had adopted CML and HzOHGP systems separately prior to this project, this operation marks the first time they have been combined.
Managed Pressure Drilling (MPD) technology was used to successfully drill challenging hole sections, and to run and cement casing strings for a deepwater campaign in the Gulf of Mexico. Because this technology offered the advantages of precisely manipulating the annular pressure using a statically underbalanced mud weight within a narrow pressure window, MPD was also employed along with real-time downhole measurements (from XACT), to run the lower completion assembly into the drilled production interval and perform downhole operations. For this specific case, the prognosed pressure operating window was around 100 psi, however; the actual window was found to be 50 psi when losses were encountered while drilling the openhole section through the target reservoir. Consequently, the completions operations required the most accurate modeling and planning to keep losses at an acceptable rate while avoiding an influx or formation collapse. MPD was utilized to precisely manage downhole pressures while running the lower completions assembly, displacing the drilling mud with completions fluids in the openhole section, and monitoring losses during the breaker acid job. A complex pump schedule was created by analyzing the pressure at several critical points in the open hole. Through back pressure management and high-resolution losses rate seen through the Coriolis flow meter, these losses were kept at a reasonable level to avoid breaching the pore pressure gradient and the wellbore stability limit. This paper describes the planning and execution processes that made this deepwater managed pressure completion job a success.
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