The Amenam-Kpono field sits astride offshore blocks OML 99 and OML 70, about 30km off the eastern part of the Niger Delta. Discovered in 1990, it is one of the largest conventional offshore developments in West Africa. It is operated Elf Petroleum Nigeria, in partnership with ExxonMobil and state-owned Nigerian National Petroleum Corporation (NNPC). Water depth is 40m.
The project comprises two phases. During phase one (2003 to 2007), all the associated gas was reinjected into the reservoirs to optimise the oil recovery rate. Within a year of the field coming on stream, peak production of 125,000bpd oil was reached. This strategy was selected because of the flaring ban coming into force in 2008. Not flaring avoids annual emissions estimated at 15 million metric tons of carbon dioxide equivalent.
Cumulative production over 30 years will amount to 588 million barrels of oil.
Phase two, which started in 2007, was dedicated to developing the associated gas from this and other fields. Ten million cubic meters of previously re-injected gas is now exported to the Bonny liquefaction plant. To replace this, 300,000 barrels of water a day will be injected. This therefore required the use of additional offshore structures as well as the use of water injection, partially replacing the gas injection that was used.
The Amenam-Kpono field was formed from sand deposited in the Niger Delta during the Miocene epoch. It consists of six hydrocarbon-bearing reservoirs ranging from 3,400m to 4,700m below the seabed.
The four main reservoirs, R4, R4b, R10 and R11, in the central and western zones for the field were developed during the first phase, with R4 containing two-thirds of the overall reserves. It is 7km long and 4km wide with an average thickness of 250m. Porosity is 15% and permeability is several hundred millidarcy. Reservoir pressure is 350bar to 500bar and the temperature is 130°C to 150°C. Oil is light at 43° to 47°.
A Q-seismic campaign carried out in 2002 gave a clear acoustic response to the oil-water contact allowing the calculation of oil in place. 4D seismic monitoring is expected to show pressure variations.
This consisted of two wellhead platforms (AMD1 and AMD2) as well as a production platform (AMP1), a living-quarters platform (AMQ) and two flares (HP and LP) on tripods. The 11,500t AMP1 platform was the largest the McDermott had ever built in its Dubai yard.
"Cumulative production over 30 years will amount to 588 million barrels of oil."
Amenam-Kpono phase two saw the addition of a wellhead platform – AMD3, a production platform – AMP2, and a 24in gas line to the Bonny terminal.
The subsea system includes 18 production wells (12 on R4), five gas injection wells (all on R4) 11 water injections wells (six on R4). The wells were drilled on the three wellhead platforms by two rigs Baltic 1 and Adriatic 1.
In 2002, the FSO Domy was replaced by the FSO Unity. Originally built in Ulsan, South Korea, it receives crude at a rate of 230,000bpd from the Amenam-Kpono field as well as the Alfia, Ime, Edikan, Ofon, and Odudu Fields. Amenam-Kpono field will provide the largest amount of input to the FSO Unity, some 125,000bpd during the first phase of its development. The field is linked to the vessel via a 38km pipeline.
The $200m FSO Unity has a capacity to store 2.2 million barrels of crude oil. It has an overall length of 300m, is 62m wide and 32m deep, with dead weight of 341,000t divided among 15 cargo tanks and a settling tank for 200,000 barrels of oil.