Drilling advances

	Vol. 232 No. 3
JIM REDDEN, CONTRIBUTING EDITOR

Self-supporting riser aims to overcome deepwater hurdle

Schematic of self-supporting riser (SSR) application with a coiled tubing intervention vessel.

As Gulf of Mexico operators struggle to understand, let alone comply with, changing ground rules, a Houston company is convinced it has a way of knocking down one of the most daunting and expensive barriers to deepwater exploration and production.

Nautilus International says it has validated the feasibility of combining field-proven self-supporting riser (SSR) technology with low-cost vessels of opportunity and coiled tubing to enable the drilling and intervention of satellite wells in as much as 10,000 ft of water. Nautilus said the technology not only promises to cut the costs of a conventional MODU intervention in half, but also brings a host of HSE benefits.

 The Research Partnership to Secure Energy for America, a US Department of Energy and industry partnership, is co-funding the project. Nautilus was awarded the contract to validate the conceptual feasibility, direct the design and construction, and proceed to a full-blown field trial. The first phase, which is to wrap up by April 30, essentially confirmed the validity of the design, including identifying and mitigating any potential hazards.

Once continuation of funding is in place, the next step would be building a prototype and finding a candidate well for a real-world trial. Tom Williams, one of three Nautilus managing directors who sat down to discuss the project, said if all goes well it’s not entirely inconceivable for a system to be in operation in the deepwater Gulf of Mexico by mid-2012. Nautilus holds an exclusive licensing agreement for the technology for the Gulf of Mexico.

Over the past couple of decades, technology advancements, particularly in flow assurance, have allowed deepwater subsea wells to be drilled up to 50 miles from the host production facility. The problem is that when production of those satellites begins to drop naturally or is otherwise restricted by some downhole problem, operators must weigh the costs and benefits of stepping in with a MODU or intervention vessel that must rely on drill pipe, tubing, wireline or electric-line equipment. There’s always lower-cost riserless intervention, but those approaches are restricted to re-entries that do not require circulation. More times than not, the benefits take a back seat, and when it comes to recompleting a satellite well to tap a more promising zone, forget it. The end result is reserves that remain in place.

“Recompletions in deep water have really been held back, as there simply is no cost-effective way to do it,” said Keith Millheim, another managing director. “Having the ability to [economically] recomplete makes a big difference in the total value of a field. While our emphasis with this project has been to cut costs, an implicit benefit is adding reserves.”

The project’s principal investigator, Charles Vemington, another managing director, said there is nothing particularly new about the individual components. Anadarko Petroleum has proven the feasibility of employing SSRs in deep water and holds a worldwide patent for the technology. The company has operated a prototype in 3,500 ft of water since 2006 off Port Isabel, Texas. And, of course, there is nothing unique about the use of low-cost intervention vessels and coiled tubing equipment for drilling, workovers, completions and cement jobs. However, Vemington said this project represents the first time the technology trio will be used as a single system, especially for deepwater and ultra-deepwater horizontal wells.

Vemington said the concept is much safer and environmentally friendlier than typical interventions. Not only are the BOP and all other well control mechanisms located onboard the vessel, but also two subsurface shutoff redundancies, a near-surface shear-and-seal and a seafloor shutoff device, help to further maintain control. What’s more, the top of the SSR is situated below the hazardous loop and eddy currents prevalent in the Gulf, and the vessel can disconnect on short notice in inclement weather and be heading off location in a matter of minutes. The SSR, meanwhile, remains connected to the subsea tree or the wellhead.

“In conventional interventions, re-entering a [live] well after the riser has been pulled can be very risky,” Vemington said. “While nothing is absolutely foolproof, this gets us much farther down that trail.”

Millheim said that while this project is earmarked specifically for the deepwater Gulf, the benefits are truly profound internationally, “where we have a lot more subsea wells to deal with.”

“For example, in Brazil they have two or three [drilling] rigs dedicated solely to interventions, and I know of at least one in Angola. In the Gulf, right now people won’t do interventions except as a matter of circumstance. The rigs simply have nothing else to do. That’s a very expensive way of doing an intervention.”