Abstract

An operator in offshore Brunei plans to abandon uneconomical wells that were completed during the 1980s. These wells have sustained annular pressure in the casing, some of which are close to the maximum-allowable annular casing pressure, and require immediate intervention to secure the wells. A rigless operation to isolate the pressure source is required to optimize future abandonment operations using a rig.

Typically, such operations include spotting the cement plug across the perforation using coiled tubing to isolate the pressure source. However, because six of the wells were located below an unserviceable helideck, coiled tubing intervention was not possible, leaving bullheading as the only viable option. The risk associated with bullheading includes the inability to access the end of the production tubing to set an additional mechanical barrier after the cementing operation because of the inability to circulate the well clean. Additional challenges included the unserviceable condition of the pipeline on the platform, which prevents flowback handling, and the lack of crane availability to conduct lifting operations. A small volume of porosity sealant polymer that is lower risk compared to cement slurry was selected to permanently shut off the zone. To overcome the surface limitations, an integrated intervention vessel operation was designed and equipped with fit-for-purpose pumping, flowback, and slickline packages.

After obtaining access to the formation through slickline, treatment was successfully pumped, and the formation sealed off effectively. The slickline mechanical plug was set in the tubing without issue, resulting in each of the wells being safely secured and an estimated 2 weeks of rig time saved for the final abandonment operations. The result marked the first successful operation to secure a well using a small volume of porosity sealant and demonstrated that a similar method and planning can be used to perform future intervention with similar surface conditions and constraints, safely and economically.

Conventional abandonment methods use a coiled tubing unit or rig for intervention. However, an unserviceable helideck restricted access to six of the wells and removing the helideck was not cost effective. This prevented the use of a coiled tubing unit or rig; therefore, bullheading was the only option. Fluid placement during bullheading operations is limited compared to coiled tubing. During the design stage, a small volume of porosity sealant fluid was selected because of the short perforation interval and tight formation.

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