WAB® overcomes depleted zone to deliver a primary well barrier

An operator in Valhall Norway was experiencing major challenges in positioning the 9 5/8” production casing shoe within the top of a heavily depleted reservoir (4,000 psi overbalance).

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 trialled 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 2nd stage cement to provide the primary well barrier pressure seal. The WAB (1214WAB5:5) fit the application in that it can provide a 5,000 psi, bi-directional ΔP rating across the barrier within the annulus.

Due to the high overbalance, the application decision, enabled by incorporation of the 1214WAB, was to terminate 12 ¼’ open hole drilling directly above the highly depleted formation.

Next step was to deploy the 9 5/8" casing complete with a 1214WAB, incorporated below a 2nd stage cement collar and above a 9 5/8" casing drill down assembly.

The 9 5/8" was then drilled in approx. 30m to engage the highly depleted formation, and when losses were instigated, a setting ball was dropped to TD, surface pressure applied against it and the 1214WAB was expanded in the 12 1/4" open hole section.

Losses in the annulus were instantly isolated upon 1214WAB setting within the open hole.

There was no need for 2nd stage cement, as losses were not as high as expected and a primary cement job was conducted, full returns witnessed and deemed a success post USIT log.

Feedback from client was that the quality of the cement job was attributed to 1214WAB providing hydrostatic support to the upper column of cement, negating any slumping into highly depleted formation.

WAB set as planned at 5,000 psi pressure applied against bumped cement plug will provide life of well cement assurance in 12 ¼” OH

WAB was set 14m MD above the DPZ and losses were minimal prior to cementing – 4.5bbls/hr
upper port collar was left permanently closed post cementing – therefore port collar tool was still required to pass through tie back PBR.