Once mobilized offshore, the HLU began well intervention operations. The unit floor, which provides a working surface for the trained crew, and the pipe handling system are pictured.

After Hurricane Katrina left an 11-well production platform listing at a 15° angle in the Gulf of Mexico (GoM), the operator was in need of a solution. According to Minerals Management Service procedures, the listing condition of the 10 live wells and one conductor on the structure called for permanent abandonment. Before abandonment activities could begin, however, the operator had to create a safe working environment on the hurricane-ravaged platform.

In a unique approach to this challenge, the operator elected not to level the entire platform, but opted instead to use a wedge deck attached to the original drill beams to allow operations to take place on a level work surface. Even with the drill deck horizontally positioned, however, the still-leaning structure had limitations on how much load the deck could bear at any one time, which would prove to be a factor in choosing a well abandonment solution.

Meanwhile, a support structure outfitted with living quarters was installed alongside the damaged platform. This innovative solution ensured the weakened structure was supported not only during abandonment operations, but also in the event of future storms.

In August 2006, a year after Katrina hit, the operator along with the intervention and well abandonment consulting team began planning an approach to abandon the wells on the listing platform. Weight considerations eliminated the option of using a drilling rig for intervention from the outset, so the operator’s original plan incorporated the use of a hydraulic workover unit to reduce the load on the wedge deck.

But there was an added complication. All 11 wells were also sloping at 15°. The solution needed to address the fact that all of the wells required straightening before they could be plugged. That’s when the intervention and well abandonment team’s new well intervention system featuring a hydraulic lifting unit (HLU) caught the operator’s attention as a more plausible solution.
Because the HLU could be easily modified for use on the damaged platform and because of its unique capability of skidding from well to well in a matter of 70 minutes, the unit presented a fit-for-purpose solution worthy of the operator’s consideration.

Planning the work

By November of 2005, the operator’s representatives had completed comprehensive research and evaluation of abandonment options, determining that the HLU would be the right tool for the job. A contract was issued, and the operator proceeded with the detailed well abandonment planning in collaboration with the intervention and well abandonment team.

Meanwhile, final stages of modification, production, assembly, and testing of the fit-for-purpose HLU system were taking place in the decommissioning yard. Given the HLU’s adaptable design, the operator was able to request specific modifications to the system, enabling it to be mounted on the wedge deck so that wireline units, coiled tubing (CT) units, and handling equipment could be controlled and maneuvered safely on the damaged platform.

As the new year began and the first phase of execution neared, equipment testing intensified at the decommissioning yard.

Among the tests were mock rig-ups that included bent casing with tubing inside designed to ensure that various downhole operations like wire-line and cutting tools would go through restricted areas and doglegs.

Consulting personnel were deployed to carry out the first phase of execution, which began with diagnostic work on the ten wells and slickline work on the production tubing. Once the integrity of the tubulars was established, the well abandonment crew pumped cement and set bridge plugs to isolate production zones. Various E-line services and equipment, including pumps, tanks, and cementing units, were used in this phase.

As the first phase was taking place, the intervention unit was being assembled and tested in the consultant’s decommissioning yard, and personnel were being trained to operate the unit. Prior to mobilization of the intervention unit, the operator shut down offshore operations, and all of the crews were deployed onshore for mock rig-up and rig-down of the system. Several days of training and a safety orientation were also conducted leading up to the subsequent execution phases. Three five-man teams participated and collectively accumulated nearly 1,600 hours of training prior to project execution.

The well abandonment contractor not only provided the well intervention unit, including related work crews and project management services, but also provided and deployed additional services and equipment, including electric line, slickline, cementing, pumping, fishing, and rental tools; tubular handling equipment; cutting, jacking; sawing and boring tools; and specialized decommissioning equipment.

Working the plan

The unit was rigged up within 24 hours of equipment deployment to the platform. Given the increased system support, the operator was able to rig up the CT injector head and unit to deploy CT to set bottom plugs on selected wells with poor tubular conditions. This decision minimized lost operation time compared to a rigless system by reducing wind restrictions and freeing up the crane to be used in offloading boats while the CT operation continued.

With the bottomhole plugs successfully set, the team rigged down the CT and began the procedure to set intermediate cement and bridge plugs. Intensive electric line work was performed on all wells to set bridge plugs, perforate, and jet-cut the tubulars where necessary.

Since the platform crane was not needed to support intervention unit operations, the customer once again benefited from improved operation efficiencies. The safety of pulling and laying down recovered tubulars was improved and the speed enhanced, which further reduced the time required to complete the operations.

In the end, the unit recovered 31,000 ft (9,455 m) of tubulars:
• 19,800 ft (6,035 m) of 23?8-in. and 27?8-in. tubing;
• 6,700 ft (2,042 m) of 75?8-in. and
95?8-in. production casing; and
• 4,500 ft (1,372 m) of 103?4-in., 16-in., 20-in., and 24-in. grouted casing conductors.

The final phase of the project included the rig-down of the intervention system. The decommissioning team started by cutting and pulling all well conductors 15 ft (4.6 m) below the mud line. Considering the 15° angle of the platform and that cutting was conducted by inside multistring hydraulic cutters using 31?2-in. internal flush drill pipe and a power swivel, this required adaptations to successfully cut and pull the conductors with nested strings of surface casing cemented inside. The remote-controlled and auto-clamping saws and boring machines improved efficiencies in this phase.

The operator and well abandonment service company completed the job on April 2, 2008, 299 days from its inception and 66 days ahead of the operator’s estimate. The work was carried out with no recordable injuries or operational and environmental incidents and with the contracted intervention and well abandonment team contributing more than 49,476 man hours to the effort.

Next in line

The intervention and well abandonment team continues to innovate solutions that will present more feasible cost-effective alternatives to conventional well intervention and abandonment practices.

A new intervention system designed to meet specific client requirements for another operator is expected to deploy in 3Q 2008.

Doubtless, future challenges and industry needs will continue to drive the development of well intervention and abandonment technology