Bonga is a deepwater prospect located in OPL 212 off the West Coast of Nigeria. Peak production for the FPSO development is expected to be 225,000 BOPD (1,490 m3/h). Since the Bonga reservoirs have poor aquifer support and are only normally pressured, the system is designed to inject up to 300,000 BWPD (1,990 m3/h) for reservoir pressure maintenance. Success of the water injection is considered quite crucial to the economics of the project. Injection must be fully operational and reliable at first oil.
The subsea infrastructure for Bonga is fairly complex and consists of two water injection risers, supporting up to 15 water injection wells. Operating such a system is challenging. Some of the subsea challenges faced during commissioning, start-up and regular operations include:
Subsea water distribution
Opening downhole FBIV valves from the FPSO
Hydrate risks during initial start-up
Injection pressure control to prevent reservoir shale Fracturing
Bonga is a deepwater oil prospect in Block OPL 212, offshore Nigeria, in approximately 1,000 m water depth. It is operated by Shell Nigeria E&P Co. in a joint venture with Esso (20%), Total (12.5%), and AGIP (12.5%). The field will be developed as a subsea network with 1.9 - 9.2 km flowline tiebacks to a permanently moored Floating Production Storage Offloading Vessel (FPSO). Bonga's peak oil production will be 225,000 Barrels of Oil Per Day (BOPD). The project requires an extensive water injection program that is critical to realising the expected hydrocarbon production volumes. The Bonga development is currently expected to recover approximately 650 - 700 million barrels of oil. However, this volume can drop to a paltry 125 million barrels in the absence of water injection.
Seawater will be treated at topsides for oxygen, biomass, solids, scaling, corrosion, and reservoir souring control. It will then be injected into the reservoirs via two 12' flowlines that depart from the FPSO. One flowline (WFL-01) serves the west side of the field, while the other flowline (WFL-03) serves the east side of the FPSO.
Water injection tees are placed in various sections of the flowlines to deliver water to the wells via well jumpers. Each water injection tee is connected to a maximum of two water injection wells. The water injection wells have subsea chokes to provide flow control for water being delivered to the wells. From the first western side water injection tee (WT-1), flowline WFL-02 branches off to cover more acreage of the field. Figure 1 shows the subsea architecture of the Bonga development.
The water injection program will be developed in phases. The first phase will consist of seven subsea water injectors, while the next phase will add up to eight more water injectors.
