A Model Approach To Well Abandonment

Multi-site, multi-operator vessel-based approach for North Sea success.

Using a diverless, vessel-based approach, Offshore Installation Services (OIS) has run more multi-site and multi-operator well abandonment campaigns than anyone else in the North Sea with more than 100 decommissioning projects since 1996. A recent campaign showcases the comprehensive, turnkey service that OIS offers for abandonment of category 1 and 2 wells, and illustrates how clients can benefit by sharing the costs of mobilisation, transit and demobilisation.

The campaign, OIS’s 16th rigless suspended-well abandonment, involved nine mudline wells (categories 1, 2.1, 2.2 and 2.3), including four on behalf of GDF SUEZ E&P UK Ltd. The scope of work for OIS included the initial approval processes; formulating the contracting strategy; developing detailed procedures; procurement; appointing specialist service providers; overall logistics; and recycling and disposing of the recovered wellheads.

The OIS team conducted this two-phase operation from a chartered, DP2-class, anchor-handling, tug-supply vessel. During phase one, a proprietary, twin, low-pressure packer tool from Acteon sister company Claxton Engineering Services was deployed through the vessel’s moon pool to set cement plugs across the casing annuli. The second phase involved abrasive severance of the wells using Claxton Engineering’s SABRE® cutting tool in water depths of 40–50 m.

For GDF SUEZ, the main aims were to abandon the wells successfully and safely without a rig and in compliance with new government regulations, as Max Proctor, the company’s drilling manager, explained. “GDF SUEZ is committed to fulfilling its responsibility to the environment as an operator and is leading the way in the North Sea with the decommissioning of redundant wells. We were proactive and started this campaign immediately to abandon all of our suspended UK wells after the request from the Department of Energy & Climate Change. We consider OIS to be a valued partner. The success of this project is testament to the team’s strong technical skills and experience.”

OIS completed the project planning in a short time frame and the operation had no lost-time incidents. However, one well presented an unusual problem when it came to removing its temporary abandonment cap. The standard interface tool (of the kind used to install the cap for the well’s temporary suspension) would not engage with the cap. As a technical report from the installation had indicated a problem with the cap, it was felt that the best solution would be to source an overshot tool in a final attempt to latch onto this piece of equipment.

The temporary abandonment cap was removed from the well using an 8¼-in.-outside-diameter, short-catch overshot tool. The tool was dressed with a 57/8-in. grapple that enabled the recovery team to engage with the cap’s mandrel, rotate the cap out and recover it to the vessel. The whole process, from engineering concept to completion, took less than two weeks, despite occurring over the Christmas and New Year holidays.

This was the first time for OIS and GDF SUEZ that this type of overshot tool had been run in hole from a vessel crane rather than using a drillstring from a rig or vessel, and possibly an industry first for the North Sea. Had this approach failed, the only option would have been a heavy-duty intervention vessel with a derrick or a drilling rig at considerably more cost and time.

Chris Hay, project manager, OIS, said, “Throughout the North Sea, many wells still require abandonment. So far, most well abandonments in the region have used a drilling rig, which is still deemed the industry standard. However, the success of our rigless campaigns may encourage operators to consider a new, low-cost approach to complying with the abandonment regulations.

“We provided a complete abandonment service during this campaign, including recovering annular well fluids to the vessel and bringing them back for onshore disposal along with the recovered wellhead casing stubs and other subsea protection structures. Furthermore, once these recovered seabed items were aboard the vessel, we tested them for low specific-activity-scale naturally occurring radioactive material. This process ensured that they were below safe handling limits and could be disposed of safely. In this case, all of the operators involved decided to donate the scrap value of the recovered materials to charity,” he concludes.

In the North Sea, weather can play a role in the success and scheduling of operations, although it does not affect the equipment once it is downhole and the winter vessel rates are usually lower. As the vessel hire is a significant proportion of the total cost, this offers a clear tradeoff with waiting-on-weather time.

Hay says, “Working on a project in this region between November and March presented some challenges and waiting-on-weather time. The wave height and swell affected the vessel station keeping, and high winds, above 30 knots, occasionally meant the vessel crane could not operate safely. In addition, strong currents sometimes stirred up seabed sediment and made it impossible to see what was happening from the images on the remotely operated vehicles’ cameras. As far as possible though, we worked around these challenges.”

OIS coped with the weather by adopting a flexible approach to the work schedule such as changing location (the weather may be dramatically better not too far away) and altering the order of the wells. This involved close liaison with all the clients and a willingness to adapt to changing conditions. This is not surprising because, according to Hay, “flexibility is one of the key factors in any successful multi-well, multioperator campaign.”

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