Prior to the installation, modeling on the impact to ECD during cementing was evaluated. The WAB is designed to be relatively transparent to cementing operations; it has a small OD, runs slick and is rugged enough to be rotated with low torque and drag effects. The modeling confirmed there was minimal risk to the primary cement job associated with the inclusion of the WAB. The 12-1/4” WAB was run in the well as part of the 9-5/8” casing string to a depth of 5,210 ft (1,588 m). This placed the WAB close to the shoe of the 13- 3/8” casing.
The primary cement operation focused on establishing good cement around the shoe of the 9-5/8” and cement quality was ensured by keeping the cement top deep within the 12-1/4” hole. Once the cementing operation was completed, the cement dart was bumped and additional pressure applied from surface to expand the WAB. The well was pressurized in steps up to 5,072 psi (345 bar), which hydraulically expanded the WAB without compromising the casing integrity.
Verification of the WAB as the primary barrier was achieved via application of surface pressure down the 13-3/8” x 9-5/8” annulus; pressure equivalent to the fracture gradient of the formation below the 13-3/8” shoe plus a 1,030 psi (70 bar) surplus. The pressure was held for 10 minutes to confirm isolation and verify the barrier.
This installation marks the first time that something other than cement has been installed in a well completion as a primary barrier. Based on the testing and qualification accomplished, the operator was able to install the WAB as a primary barrier without the need for a dispensation from the authorities. Since this first operation, a further two wells have been completed and a fourth well is in planning for the client.