Abstract
This abstract presents the evolving scale management strategy over the life of the Pelican field and the recent success in enhancing late life production.
The subsea Pelican gas lifted field is a water injection supported oil field tied back to the Cormorant Alpha platform and has been in production since 1996.
In early field life, the initial scaling assessment predicted barite scale deposition in the tubing, prompting the adoption of preventive inhibition measures. Scale dissolver treatments and inhibitors were dutifully employed throughout most the field's life, but some wells experienced productivity decline due to scale inhibitor injection and some well abandonments recovered clean tubing with no scale deposits.
As new wells were to be drilled in late field life, a reassessment of the scale management strategy was required and core studies were commissioned to assess the inhibitor impact on return permeability, which revealed a significant reduction in productivity. Moreover, a study by Heriot Watt University indicated that the risk of barite scaling was confined to the reservoir, with a low probability of deposition in the wellbore and this led to the suspension of further inhibitor treatments.
However, during the period 2016 to 2018 a significant production decline in the Pelican field was observed. After a rigorous well performance and scaling tendency reviews, the decline was attributed to calcite deposition which ran contrary to both production and abandonment experience. Challenging accepted field practice, required multiple gated approval processes before finally obtaining approval to proceed with the subsea intervention to restore productivity.
Consequently, extensive carbonate scale was removed from high up in the tubing through to the reservoir section in the biggest producer PuP18s1 in 2019 with the MSS1 rig. A combination of multiple runs of chemical dissolver and CT milling were employed to remove scale restrictions to increase well production rate. Scale treatment of the P18S1 well successfully increased production from the Pelican field by 40%.
After successful scale removal, a remediation strategy was put in place, involving yearly acid dissolver treatment bullheading to the subsea wells. This approach has achieved stable production from 2021 to 2023, with three successful acid dissolver treatments and no significant decline in the production rate.
