FIRST WELLTEC® ANNULAR BARRIER RUN AS PRIMARY WELL BARRIER, PREVENTING SAP

Welltec Annular Barrier Completions solutions

Background

The annuls between the 9-5/8” and the 13-3/8” casing strings within a Norwegian field development had historically exhibited pressure buildup at surface on many wells. It had been determined that the source of the pressure was a gas charged formation just below the 13-3/8” shoe. Obviously, for the operator, eliminating surface annular pressure (SAP) was a priority along with easy barrier verification over the lifetime of the well. To eliminate the SAP several methods had been trialled over the years including single stage cementing, second stage cementing, external casing packers and liner tie back solutions. All of these solutions had failed to resolve the problem. Meanwhile, the Welltec® Annular Barrier, WAB®, had been successfully deployed by the operator for zonal isolation in a number of wells across various reservoir sections. Subsequently, it was proposed by Welltec® as a possible, alternative solution to eliminate the SAP.

In order to be utilized as a primary well barrier, replacing cement, the solution had to pass a number of significant criteria. It was carefully reviewed by the operator’s Well Integrity team to ensure that the system complied with their own company standards and the Norsok D10 guidelines. Meanwhile, further qualification of the intended solution, a 12-1/4” WAB, was completed to extend its certifications from the ISO 14310 V3 standard to V0.

OPERATION

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.

ACHIEVEMENTS

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.

This installation marks the first time that something other than cement has been installed in a well completion as a primary barrier.