The number of new deepwater wells has decreased as part of the general decline in the offshore market, but the number of wells requiring plugging and abandonment (P&A) still rises as assets age.

At the same time, the regulatory requirements to P&A those wells continue to get more stringent. As a result, the cost to P&A a well has risen exponentially and looks set to continue increasing.

Wild Well Control, a Superior Energy Services company, has developed a subsea P&A approach that is changing the way the industry performs deepwater P&A operations by offering a rigless, riserless intervention system to meet the demands of increasingly stringent regulatory bodies.

The DeepRange tool, used in conjunction with the 7Series intervention system, is certified to operate in water depths of up to 3,048 m (10,000 ft) and a maximum working pressure of 10,000 psi for P&A operations. It also has gained full approval from the Bureau of Safety and Environmental Enforcement (BSEE) in the U.S. Gulf of Mexico (GoM).

Subsea P&A in the GoM
Moreover, all that is required for system deployment is the use of a multiservice vessel, although current operations are being conducted from a mobile offshore drilling unit due to current market pricing.

The new tools and techniques have been used on a subsea P&A operation underway in the GoM and already have exceeded the expectations of Wild Well Control as well as those of the operator.

When compared to more traditional P&A methods such as “cut and pull” of casings, the DeepRange system leaves casings intact, which is less invasive and therefore much less costly. Other methods such as “perf and squeeze”—while less expensive than “cut and pull”—can provide cement plugs of dubious quality and permanence.

The circulated plugs rendered by the DeepRange methodology provide the same quantitative qualities of “cut and pull,” while still being price competitive with “perf and squeeze.”

How does it work?
To simplify a complex process, the DeepRange/7Series subsea P&A system can best be explained in this 10-step process:

• Step 1: Pre-operational engineering and planning involves creating and resolving interfaces with the well and vessel of choice, developing detailed operating procedures and creating a project execution plan.

• Step 2: Crews perform the temporary abandonment of the well, cutting and pulling the tubing before installing a cast-iron bridge plug and packer.


• Step 3: The upper assembly—consisting of an isolation bushing, tubing-conveyed perforating guns and a telescoping joint—are landed and latched into the packer.

• Step 4: The upper tubing is conveyed and the lower standard perforating guns are fired into the B annulus.

• Step 5: Circulation is established through the tubing, into the lower perforations, up the B annulus, out through the upper perforations and back up the production annulus. The isolation bushing diverts flow to the return lines.

• Step 6: The binary plug is circulated into the B annulus. After waiting on the cement to harden, a mandatory pressure test is performed.

• Step 7: The upper tubing is conveyed, and the lower standard perforating guns are fired into the C annulus.

• Step 8: Circulation is established through the C annulus as with the B annulus previously.

• Step 9: The binary plug is circulated into the C annulus. The plug is left in a “balanced” condition with the production annulus. After waiting on the cement, testing is performed.

• Step 10: The upper assembly is unlatched from the packer and pulled from the well. A cast-iron bridge plug is set above the highest perforations and cement is bailed as per regulations.

Complementing the operation is the wholly in-house Wild Well Advanced Engineering group that provides any necessary computational fluid dynamic, structural and thermal analyses. The DeepRange/7Series subsea P&A system delivers an extremely cost-effective operation using a binary plug comprising resin and cement for a long-lasting, effective alternative to traditional P&A operations.

Annular isolation requirement
Wild Well had worked on 11 wells previously where the temporary abandonment (TA) of a subsea well was accomplished with the 7Series riserless intervention system.

While TA of a subsea well with a riserless system from a vessel of opportunity was a significant accomplishment, the subsea team set out to develop tooling to fulfill the regulatory requirement to provide isolation of the outer annuli of the well. This requirement is what prompted the development of the DeepRange methodology.

The current DeepRange/7Series riserless intervention suite has so far successfully performed full P&A operations on seven subsea wells (with wells eight and nine in progress simultaneously) in the ultradeepwater GoM months ahead of schedule. Specifically, crews have used the DeepRange tool in each of the wells to isolate outer annuli by circulating more than 61 m (200 ft) of cement in place and pressure-testing the plug, which exceeded BSEE requirements.

Wells requiring temporary abandonment, pulling of production tubing and isolation of a single outer annulus have taken an average of 15 days to fully complete. One of the wells that required three annuli to be isolated was completed in only 20 days. This well in particular would have required the cutting and pulling of three successive strings of casing if done with the traditional “cut and pull” method at far greater cost and time.

Advantages
The differences between the 7Series and DeepRange tool and other P&A techniques are many. The first is water depth—the 7Series system is a 10,000-psi, 3,048-m graded system—with the deepest well P&A to date using the system located in 2,244 m (7,362 ft) of water. This water depth is beyond alternative annular isolation tools on the market. Other potential competitors are operators of subsea intervention systems similar to the 7Series, but none have a system that can perform annular isolation, only the “perf and squeeze” method.

The system also is deployed underneath a full pressure control assembly so any pressure control issues on a particular well can be mitigated. With subsea wells it might also not be known if an annulus has pressure, if that pressure is going to be sustained or if it is going to bleed off. There are still many unknowns. Such wells also can be sub-hydrostatic, or on vacuum. The Wild Well system gives the flexibility to address unplanned circumstances while performing the annular isolation.

The 7Series was originally designed for live well intervention and, as such, Wild Well can accomplish a multitude of intervention tasks. Bullheading chemicals, perforating, sliding sleeves and logging can all be accomplished and present an added bonus for an operator who not only has P&A liability but also wells that require intervention to optimize production.

On a larger campaign, wells could be restimulated and worked over with wireline to increase production. If certain wells do not “come back,” they can then immediately be fully and competently P&A, all with a single mobilization.

Deepwater operations have become synonymous with high complexity and risk, and subsea wells were therefore traditionally expensive to work over and ultimately P&A. By taking an outside-the-box approach to intervening on subsea wells, a suite of tooling and methods is now available that can significantly decrease the costs of managing brownfield subsea assets.