Cement Bonding Improvements via Specialized Spacer Technology on the Norwegian Continental Shelf

Abstract An operator on the Norwegian Continental Shelf (NCS) anticipated significant challenges achieving the necessary barriers on the 9 ⅝-in casing, which required two 30-m sections of isolating annular cement above the reservoir. With a high inclination angle of over 75 degrees, combined with the inability to rotate the liner / casing, and low displacement rates complicated the process. To improve barrier success rates, a new solution for cementing pre-flush / spacer fluids was required. To address these challenges, a novel approach has been proposed that involves the combination of fibrous material and a surfactant package within the spacer. This innovative technology is highly effective in both water-based mud (WBM) and non-aqueous fluid (NAF) environments. The procedure involves pumping this specialized spacer ahead of the cement slurry. The fibrous material plays a crucial cleaning role by mechanically scrubbing and removing residual drilling fluid from the casing and formation. In parallel, surfactants work to water-wet the cleaned surfaces, promoting better adhesion and bonding of the cement to both the casing and the formation. The first job was successfully executed, implementing this technology on a 9 ⅝-in casing cement job resulting in 459-m of isolating cement being placed and logged in the annulus (the longest continuous intervals reached up to 69-m in length). This success allowed the rig to continue drilling as planned and eliminated the need for a 7-in contingency liner to achieve the required well barrier acceptance criteria. Cement evaluation from offset wells typically showed that the length of qualified isolating cement ranged from between 71 and 116-m in total, with the longest continuous interval being around 27-m. By utilizing this specialized fiber technology, annular cement bond logging results improved substantially by an additional 343-m without the operator requiring internal dispensations to qualify the barriers and continue operations. Subsequently, multiple cement jobs using this technique have been executed flawlessly in the field, meeting the job objectives on each occasion. This case study demonstrates a successful cementing solution to significantly improved cement bond log results and meets the required cement barrier criteria. This paper will describe the best practices and lessons learned that the operator in question subsequently incorporated into future operations, and which other operators with similar scenarios in the NCS are evaluating to adopt in the future.