The petroleum industry has made significant investments and extensive research to rectify well integrity issues, one particular failure mode relates to the structural degradation of the surface and conductor casing strings by the effects of corrosion. Historically, and by convention, the inability to provide integral barriers in the 9⅝″ × 13⅜″ casing annulus is resulting in wells being abandoned. Section milling to restore annulus integrity and the use of external casing patches to replace failed casings are two of the innovative approaches that we utilized in offshore wells to recover annulus integrity and as such preventing reservoir fluid migration to surface. These approaches have proved successful as they provided real economic and environmental advantages. We have proven that wells can be put back on stream with greatly reduced CAPEX and OPEX exposure, negating the need to drill new replacement wells; we achieved tangible commercial benefits and at the same time reduce our environmental risk exposure.

Our remediation engineering design focuses on the application of a novel strategy for an offshore well that had failed Annulus-B (9⅝″ × 13⅜″ casing annulus). The failure was detected during planned annulus monitoring. The annulus pressure test failed and testing fluid was observed exiting from the conductor. The remediation action involved section milling and the placement of cement to regain annulus integrity. The operation commenced with standard workover practices for the completion recovery, followed by the running of cement, noise, temperature and corrosion logs in an effort to evaluate the cement quality behind 9⅝″ casing above the reservoir and gain corrosion mapping of the 13⅜″ casing.

The noise/temperature logs indicated a leak point at 4500 feet and the annulus space was hydro-tested which resulted in returns being observed at surface, confirming a direct leak path from the 9⅝″ × 13⅜″ casing annulus to the 13⅜″ × 30″ casing annulus. The cement bond logs indicated poor cement behind 9⅝″ casing above the reservoir. However, the results from metal thickness detection logs indicated insignificant corrosion (˜15%) for 13⅜″ casing, eliminating the need to recover and replace this casing string. The decision was taken to place two cement barriers behind the 9⅝″ casing, above and below leak point, and an additional barrier would be installed with the use of a 7″ tie-back casing string. The planned strategy was successfully implemented and the integrity of the producer well was restored with two competent 100’ cement barriers behind 9⅝″ casing, above and below the leak depth, and a 7″ tie-back casing string was also cemented all the way to surface.

As a result of this remediation, the production rate for the well was restored and provided an additional 200 BOPD as compared to expected production rate. Adopting the above methodology resulted in approximately 50 days rig time giving significant cost savings and negated the requirement to permanently abandon this well and to drill a replacement well.

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