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.

Managed pressure cementing (MPC) is an important technique for primary cementing operations in wells with narrow pressure margins between the pore and fracture gradients. This paper presents the design considerations, methodology and results of two deepwater MPC operations conducted to cement production casing strings within a target operating window of approximately three tenths of a pound. Slurry densities commonly lead to high equivalent circulating density (ECD) levels during cementing operations. This condition, combined with mud weights conventionally designed to be above pore pressure, typically results in downhole pressures which approach or exceed the fracture limit. Commonly, operators implement strategies to mitigate undesired results during the cementing phase, however, in most cases the root cause of the problem cannot be adequately addressed by taking a conventional approach. Modern transient hydraulic modeling software permit the calculation of adequate surface pressure levels to control the annular pressure profile during the different stages of a cementing operation. Based on a predetermined annular pressure target, different variables can be designed to produce surface and downhole pressures within existing limits of a particular operation. This capability combined with modern managed pressure drilling (MPD) systems enables accurate control of the annular pressure profile during cementing and allows obtaining near constant bottomhole pressures (BHP) throughout the cement placement operation while using statically underbalanced mud columns. This case study presents an overview of the engineering process used to plan and design the managed pressure cementing operations on two wells and the results obtained. The results of this study demonstrate the advantages of using modern MPD systems over the conventional approach when it comes to primary cementing within narrow downhole pressure windows often encountered during deepwater drilling operations.

One of the major technical challenges to this project was placing horizontal open hole gravel packs (HzOHGP) within the narrow pore pressure to frac-gradient (PPFG) margin in the target reservoirs. This paper addresses the steps taken to overcome this challenge. To maximize the use of the narrow PPFG margin, the project combined a managed pressure drilling (MPD) system with low gravel placement pump rates made possible by an ultra-light-weight proppant (ULWP).  Of the MPD systems available, the Controlled Mud Level (CML) system was selected over the Surface Back Pressure (SBP) system for several reasons. It enabled conventional gravel pack pumping operations and equipment and it accommodated the brine weight needed to inhibit the shales. A series of lab tests showed that the completion fluid density required to inhibit the reservoir shale reactivity was only possible using CML. An overall evaluation of CML showed that it was most suitable and offered the greatest flexibility for the gravel pack job design. The special ceramic ULWP had to be qualified and tested.  The qualification testing ranged from standard API and compatibility tests to full scale flow loop testing. The flow loop tests were needed to measure the ULWP transport velocity for the target wellbore geometry. Understanding the transport velocity is critical for gravel pack design and job execution planning. Once MPD and ceramic ULWP were selected, the gravel pack placement operations were simulated to demonstrate that their features increased the likelihood of successfully gravel packing in the target reservoirs.  Small PPFG margins decrease the probability of success of placing a HzOHGP.  In the target formations, the pressure margin is insufficient to safely execute HzOHGP conventionally; instead, the project combined MPD and the low pump rates facilitated by using ULWP to control circulating pressures to stay inside the narrow margin and place the gravel packs. The integration of CML and ULWP into in a gravel pack operation to control circulating pressures has never been done. The concept and its successful field implementation are industry firsts.