DARA – A Marginal Oil Development Under Offshore Gas Brown Field Facilities in Gulf of Thailand GoT
Authors: Yuhun P. , Tangsadthakun C. , Attavitkamthorn V. , Chirataanyapak R. , Martin A. , Jarnsuwan P. , Boonmeelapprasert C. 
Published: November 2024

DARA area, which comprises both gas and oil plays, is a critical resource of GoT field to feed the domestic gas consumption. The presence of marginal oil reserves, approximately 7000 Mbbl, poses challenges to pipeline flow assurance and the existing central gas-processing platform. Therefore, the objective of this work is to turn this marginal oil resources into production without compromising our gas production and nomination. To facilitate oil production, wax and separation studies are conducted across three areas: 1) the remote wellhead platform (WHP), 2) central processing platform (CPP), and 3) subsea pipelines. At WHP, chemical injection bottle-test, like demulsifies, to address separation issues. Mono-trip-gas-lift completion with small footprint rental well-unloading units are prepared for enhancing oil production. At CPP, heat tracing and insulation are designed to prevent wax deposition based on cloud-point (122°F) and pourpoint (86°F). Separator efficiency studies at each CPP separator use production peak profiles for worst-case scenario design. Aspen-HYSYS software provides steady-state thermodynamic modeling and operational unit calculations for all equipment's safety assessment. The assessment at CPP revealed no issues with separator efficiency concerning gas or liquid retention time. To cope with increased liquid production, the control valve sizes of the Inlet Separator (IS) condensate outlet and Condensate Surge Drum (CSD) water outlets are recommended to enlarge. Installing a chemical injection port upstream of the IS enhances separation efficiency, while heat tracing and insulation are recommended for instrument equipment. At WHP, the chemical injection bottle-test suggests injecting demulsifier at 100-200 ppm and pourpoint dispersant at 500-750 ppm to reduce the pourpoint to 60°F (below vessel temperature). At pipelines analysis from WHP to CPP, wax buildup isn't problematic due to pigging operations. Considering condensate pipeline from CPP to tanker, OLGA software advises keeping oil production below a 24% oil-condensate blending ratio to minimize wax deposition (no-pigging option), averting potential pipeline corrosion from sulfate bacteria. This ratio also aligns with our contracted tanker's API sales specifications. Consequently, the existing gas facility upgrade, with optimal chemical injection, enables marginal oil field development. Wells currently produce 2000-3000 Bopd without separation or wax issues. Gas-lift from well-unloading units plan to start in Q4'2024 to boost oil production.

Overall, the paper shares the knowledge, challenges, and cost-effective strategies for developing a marginal oil within an established small-footprint offshore gas brown field facility. The initial step involves upgrading the facility within budget constraints to initiate oil production and address flow assurance issues. Subsequently, focus will be shifted to implementing gas-lift operations using well-unloading units, followed by secondary enhanced oil recovery through a compact seawater flooding unit in the near future.