Building a connection

Jerry Lee takes a look at Weatherford’s new subsea wellhead connector, which allows operators to use vessels of opportunity for P&A work, reducing the cost of decommissioning operations.

Clients observe a multi-operator factory acceptance test of the SWC at a Weatherford research and development facility in Aberdeen, Scotland. Photo courtesy of Weatherford International.

Abandonment and decommissioning is set to rise as older oil and gas developments become costlier to maintain and operate during the current downturn. Research and Markets forecasts a 20.4% CAGR out to 2020 for the global offshore decommissioning market. In the North Sea alone, Douglas Westwood projects that US$48 billion will be spent on plugging and abandonment (P&A) work (OE: June 2016).

Several companies are working to bring down decommissioning expenses. Weatherford has created a subsea wellhead connector (SWC) with this goal in mind. The SWC can be deployed from a vessel of opportunity (VOO) – a mobile offshore drilling unit (MODU) or monohull vessel – for P&A or re-entry operations.

Abandoning a subsea well is completed in three phases: primary reservoir isolation, intermediate reservoir isolation, and environmental isolation with wellhead recovery. Typically, a MODU is contracted for the entire operation, however, Weatherford’s new SWC seeks to change this by performing phase three with a less expensive monohull vessel, allowing the operator to save 40-60%, conservatively, on this phase, says Steven Canny, engineering lead, Well Abandonment and Intervention Services, Weatherford.

The SWC is a mechanical connector that can latch onto a subsea wellhead (via rotation) and allows electro hydraulic continuity to the bottomhole assembly for P&A or intervention work. The design is based on Weatherford’s MOST (mechanical outside-latch single-trip) subsea wellhead retrieval tool, using its latching mechanism.

Deployed using a heave-compensated wire, tubulars, or a combination of the two, the SWC's latching system enables it to interface with common mandrel and hub profiles. Images courtesy of Weatherford International.

Using the MOST tool as a base, engineers redeveloped the connector to be run with tubulars, including intervention riser, or on a heave-compensated wire and a work-class ROV (remotely operated vehicle) – enabling the cost effective rigless deployment. ROV guide arms were added to the lifting sub and a breakthrough was added to allow umbilicals or electrical flying leads to access apertures in the lower interface of the connector allowing electro hydraulic continuity to the severance tool or well. ROV stabilization bars, position markings, and a secondary failsafe mechanism were also added to the connector.

The SWC can be used on all common 18.75in bore wellheads, with mechanical, abrasive, or explosive severance tools for P&A campaigns, and a small re-entry mandrel seal assembly for interventions. Deployment can be vertical or horizontal, and operations would only be limited by the ROV’s limitations.

From when the project was sanctioned to the factory acceptance test (FAT), the development process came about quickly.

“It took 28 days to go from a kickoff meeting, sitting in an office, to delivery at a client-witnessed FAT,” Canny says.

Since then, four P&A campaigns on the UK Continental Shelf (UKCS) in the North Sea have ran the SWC.

“The first campaign was a multi-operator campaign for one well using a monohull anchor handling vessel (AHV),” Canny says. “This proved to be the most challenging deployment; however, it displayed the value of the SWC, without which the campaign could not have been performed.”

Performed in September 2015, the SWC was horizontally deployed through a small moonpool on an AHV with minimal on-deck equipment in 286ft water depth. The objective was to recover a 10M hub profile wellhead for a multi-operator intervention and P&A campaign. To achieve this, the operation required an abrasive cutting tool, supplied by one of the SWC project’s partners, to cut through 30in, 13.375in and 9.625in casing. During operations, the ROV was able to hold onto the SWC; however, as it began thrust for rotation, the manipulator arms on occasion slipped down the bar. This led to modifications of the API ROV interfaces to allow the ROV to handle the tool better. On the lifting sub, the ROV guide arms were lengthened and a positive stop was put on the end to give the ROV more area to grab and prevent it from slipping during rotation. On the connector, the diameter of the stabilization bars was increased from the API recommended 0.75in to 2in so the ROV could hold the tool more securely. This campaign also led the tool to be redesigned with a 4.5in box connection, so it could accommodate drill pipe and a pad eye crossover to give the operator more flexibility on a campaign.

Once the cuts were complete, the tool and wellhead were recovered over the side of the vessel. The operator's savings were significant on this campaign due to the exceptionally low day rate and AHV availability compared to an intervention vessel or MODU, Canny says.

The SWC was then deployed on three more UKCS North Sea campaigns.

“The second and third campaigns were for tier-two operators from monohull intervention vessels with deployment through an intervention tower,” Canny says. “The fourth campaign involved nine wells using a MODU and was run on drill pipe, which enabled the operator to run abrasive technology from a MODU for the first time globally – demonstrating the flexibility and capability of the SWC, and the value it delivers.”