One-trip abandonment system reduces rig time, costs

The CX-2 bridge plug allows for quick cement placement with minimal disruption.

Well abandonment can involve isolating and abandoning several sections of a well, resulting in a costly, time consuming process. Multiple cement plugs and numerous trips are required, and it is essential that the plug is set in clean casing. Coretrax, a UK-based specialist in wellbore clean-up and abandonment, has been working since 2009 to streamline this process by improving the way bridge plugs are installed during wellbore abandonment programs in the North Sea, having helped successfully abandon 84 wells between 2013 and 2015.

ONE-TRIP ABANDONMENT SYSTEM

The Coretrax one-trip abandonment system has reduced rig time, costs and the risk associated with additional trips. The system has been enabled through the use of four products: CX-2 bridge plug, CX-drillable brush, inflation support tool (IST) and the CX ball. The CX drillable brush is utilized to perform scraping to set the plug and cement in the same run, in a safe and efficient manner. The integration of a drillable brush (or sacrificial scraper), with the bridge plug, ensures clean casing to provide a solid base for a cement bond, reducing any micro-annulus. Furthermore, it ensures a clean area for plug setting.

The CX-2 bridge plug minimizes gas migration and is activated by dropping a ball from surface, which is then set with the application of pressure and overpull. Disconnecting from the plug is achieved through rotation and leaves the setting mandrel slick with the pipe, with a substantial ID for cementing operation. A slimline-setting mandrel allows for quick cement placement and minimal disturbance when the mandrel is pulled through the cement.

DECOMMISSIONING CAMPAIGN

The capabilities of these products were demonstrated during an extensive decommissioning campaign in the UK North Sea that employed a semi-submersible rig and involved 30 well abandonments over a three-year period.

The operator recognized there was a requirement to remove large amounts of swarf from the ram cavities, to protect BOP equipment and components in the mud circulating system. Section milling of casing was required on most wells to set cement barriers, which required Coretrax to run in excess of 45 bridge plugs and cement retainers, including some with a drillable brush.

Appreciating the volume of potential debris required to be recovered, Coretrax identified that magnets with a large surface area would offer the highest carrying capacity for swarf, and removed up to 56 kg of an average return per operation. The magnet technology was coupled with high-pressure jets to achieve a high standard of BOP cleaning on every run.

Prior to having a BOP cleaning assembly on board, the BOP was pulled between every well to be cleaned by hand, resulting in several kilograms of debris having to be removed by deck crew. However, since the BOP jetting assembly has been available, the debris has almost been eliminated, therefore minimizing time spent on these activities.

The CX-Ball is a foam wiper ball wrapped in a soluble material and shipped in a sealed transport tube. The transport tube is then placed over the drillpipe connection, allowing the ball to be smoothly installed into the drillpipe. These were supplied to the operator to clean the pipe after cement operations. Once the ball makes contact with the well fluid, the soluble material covering the ball dissolves, allowing the ball to reform to its normal shape as it is pumped down the string to clean the ID of any residual cement. The CX Ball reduces manual handling and saves rig time.

As well abandonment continues to be a costly and lengthy process, the utilization of products that offer cost and time efficiency as well as safety benefits, will be imperative for efficient and effective decommissioning operations.