WELLTEC® ANNULAR BARRIER OVERCOMES DEPLETED ZONE TO DELIVER A PRIMARY WELL BARRIER

Welltec Annular Barrier Completions solutions

Background

A Norwegian Operator was experiencing major challenges in positioning the 9 5/8” production casing shoe within the top of a heavily depleted reservoir. The low pore pressure in the depleted zone had repeatedly caused severe losses during the cementing operation which resulted in difficulties to construct a primary barrier using cement within the 9 5/8” to 12 ¼” annulus. Many solutions had been trialed with varying degrees of success; the majority resulting in reliance upon contingency plans, bringing increased cost and risk.

Continuing to look for a solution, the operator screened and subsequently elected to trial the Welltec® Annular Barrier, (WAB®), a rugged, fullbore annular barrier, in combination with cement to provide the primary well barrier pressure seal. The Welltec Annular Barrier (product code1214WAB5:5) fit the application in that it can provide a 5,000 psi, bi-directional ΔP rating across the barrier within the annulus. It runs slick with a 11.37” running OD, opens to a maximum 13.8” setting diameter and is qualified to 5,000 psi V3 leak criteria under ISO14310 standards.

OPERATION

The WAB was assembled on the OD of the 9 5/8” casing string along with a 3rd party cement port collar positioned shallow of it. The casing was run to a depth of 2,655m without incident, the rugged WAB able to withstand liner rotation as needed. The setting depth was 14m shallow of the depleted zone formation top. Because of its slick, nominal upset OD, the WAB is generally transparent to the primary cementing operation and poses limited to no risk. The primary cementing job was completed with liner rotation, the cement top plug bumped and pressure applied gradually from surface to expand the WAB.

At 5,000 psi surface pressure, the WAB was fully expanded and the port within the 9 5/8” casing was isolated. This returns the full burst and collapse pressure rating of the 9 5/8” casing. On completion of the job, the operator confirmed a successful primary well barrier had been established comprised of both the cement and the WAB.

ACHIEVEMENTS

Capitalizing on the unique capabilities of the Welltec Annular Barrier, an operator in the North Sea overcame a longstanding, well integrity challenge which had resulted in excessive contingency cost and risk over the years.

Incorporating the 1214 WAB into the well construction allowed them to achieve a primary well barrier between the 9 5/8” and the 12 1/4” open hole efficiently and effectively despite a heavily depleted reservoir section.

Proper contingency planning was accomplished ahead of time, and although not required, aided in risk mitigation and cost control. The capability of the WAB to expand quickly from surface, despite the presence or lack of cement enabled the use of a port collar to increase the success of a secondary cement job for primary barrier construction.

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Contingency

In the event there was communication to the depleted zone during the drilling or the subsequent cement operation, contingency plans had been established to capitalize further on the WAB’s characteristics. The primary cement operation would still have been attempted and the WAB® expanded as described previously, but now without cement around it. Next a second stage cement operation would have been conducted through the port collar, the WAB® isolating the cement from the depleted zone below while diverting the cement upwards and acting as a base for the cement.

Capitalizing on the unique capabilities of the Welltec Annular Barrier, an operator in the North Sea overcame a longstanding, well integrity challenge which had resulted in excessive contingency cost and risk over the years.