Brownfield - Debottlenecking To Safely Extend the Operational Capacities of Existing Facilities
Authors: Gaidhani Hemraj K , Hollaar Mark 
Published: June 2014

For most of the Early Oil Production (EOP) facilities in early days of the field life, higher oil production is expected due high reservoir pressure. In this specific case study, oil production has hit the FPSO topsides design limit of 100 kbopd with only 5 wells connected. Most of these wells were choked to 30–50% to limit to oil production within installed name plate capacity of the FPSO.

Therefore to take advantage of low GOR and high dry oil production during early field, Client has requested SBM to undertake the study to identify the maximum oil production without compromising Process safety and major modifications.

The main bottlenecks to increase the crude production above the design capacity are identified as - increased crude temperature results in non-stabilized crude entering into the cargo tank mainly due to limitation on utility systems. To further increase production separator capacity is a bottleneck.

Increased Temperature Non-Stabilized Crude: Based on the oil composition, stabilization of the crude before leaving the topsides is an issue. With increase in the production and limitation on utility system, enough heat is not available to flash-off light components and/or cool the crude down before entering cargo tank to prevent any further flashing in cargo tank. These flashed off gases will be vented through the cargo vent system along with displaced gases (which is significantly higher than flash gases). The cargo vent system is designed for vent-load during cargo terminal loading and therefore crude flash rates will not be anywhere near the design capacity of the vent system.

Limitation of Utility Systems: As expected, all utilities systems are designed for 100 kbpd liquid production and any increase in production will have impact on the utility balance. To cater additional flow, either modifications are required in the existing system (e.g. additional duty, exchanger modifications, etc) or the optimization of the existing system is required.

Separators Capacity: As long as water cut is negligible and small quantity of the water can be allowed to settle in the cargo tank, current crude oil production can potentially be increased with separator operating as two phase separators.

In summary, 120,000 bopd crude productions can potentially be achieved immediately without any modifications if slightly higher temperature crude along with some additional hydrocarbon venting of the gases is allowed from cargo vent to atmosphere. The changes in the process parameters (Pressure and Temperature) will allow optimization of the utilities and meeting the crude storage specs, without any physical modifications.

The actual field trial did match with the study results and production was raised above the design capacity without much process stability issue. Therefore, this type of the study provide a quick but thorough way to investigate the way forward to improve the production without compromising the safety limits, allowing the operator to take full advantage of favorable reservoir performance to optimize the capital value of the asset.