The goal is to reduce the costs and risks of drilling in deep water by developing a relatively low-cost yet reliable dual-gradient drilling (DGD) system that employs standard mud pumps to inject rugged, durable, and removable lightweight hollow glass spheres into the drilling riser at the seafloor, reducing the density of the drilling mud in the riser. A subsequent reduction in the borehole pressure below the seafloor results, and the difference between the fracture gradient and borehole pressure widens. This mitigates the possibility of lost circulation and other expensive problems, such as an environmental blowout and loss of well or life.

Mauer Technology Inc. – Project management and all research products

Location:
Sugar Land, Texas 77478

Drilling in deep water is complicated and expensive due in part to the column of drilling mud in subsea drilling risers. Under such conditions, fracture and pore pressure curves are close together, often necessitating a large number of casing strings. DGD systems reduce this problem by reducing mud hydrostatic pressure in the riser near the seafloor, typically by using pumps located at the mudline.

A number of DGD systems are currently being developed (e.g., MUDLIFT, DEEPVISION, and Shell SSPS). These require expensive, complex seafloor pumps, which have a high risk for failure, are unable to handle large kicks, and are time-consuming to repair or replace. Approximately $100 million have been spent during the past five years (1998-2003) on DGD to reduce seafloor drilling problems. The hollow sphere DGD system, envisioned by this project, requires no equipment on the seafloor, is relatively low risk, since conventional surface pumps are used, can handle any size kick, can be used on any deepwater rig, and is quicker to implant and maintain.

Maurer Technology, Inc. (MTI) assembled a joint industry project (JIP) consortium of nine operators, service companies, drilling contractors and national oil companies to support research for a new hollow sphere DGD system. This system utilizes mud pumps and surface separation equipment on the rig, eliminating the need for complex, expensive, and less reliable seafloor mud pumps. They pump hollow spheres (glass, composite, or plastic) to the seafloor, injecting the lightweight spheres into the riser.

A $1.8 million Phase I funded by the JIP showed that hollow spheres could be pumped in to a well. A difficulty encountered included separating the spheres from a polymer mud supplied by Halliburton due to high mud viscosity at the low shear rates. As a result, an excessive amount of this polymer mud flowed across a screen with the beads instead of through the screen. At the completion of the Phase I project, it was concluded that the hollow sphere system would not work effectively with the polymer mud tested. ExxonMobil and Shell engineers proposed that additional sphere separation tests needed to be conducted with weighted oilfield waterbase and oilbase muds to determine if the DGD system would work with these muds.

BP (British Petroleum) estimates that a DGD system can save $9 million per well in the Thunderhorse Field and Conoco estimates it can save $5 to $15 million per well in its deepwater operations. Unfortunately, previous DGD development projects have been unsuccessful due to the high costs ($20 to $50 million) and reliability problems with seafloor pump systems.

Noble plans to commercialize this system with a service company partner that will market and operate the DGD system on Noble’s and other drilling contractors’ rigs.

• Carried out a three-part, Phase I research program to evaluate and design a dual-gradient drilling system utilizing hollow sphere to lighten the fluid column in subsea risers, and
• Prepared and submitted a final report on Phase I work.

The DOE-funded tests showed that the spheres could be pumped with conventional oilfield centrifugal and triplex mud pumps and separated effectively from both oilfield waterbase and oilbase muds using conventional oilfield shale shakers and hydrocyclones reduce the density of the drilling mud in the riser.

and Remaining Tasks:
DOE’s participation in this project is complete. The remaining tasks and phases will be undertaken by industry. An $8 to $10 million Phase II development project is under consideration by the JIP participants. During Phase II, all components of the system capable of drilling to water depths of 10,000 ft will be developed and tested in shallow land wells. Following these land tests, the system will be tested at water depths of 1,500 to 2,000 feet if funding permits. If Phase II is successful, commercialization of the system will be pursued.

$200,000

$1,600,000

NETL – John D. Rogers (jrogers@netl.doe.gov or 304-285-4880) 
Maurer Technology – Tom William (twilliams@noblecorp.com 281-276-6713)