TFE nearing production from Nigeria's Amenam field

Nick Terdre
Contributing Editor

TotalFinaElf is close to bringing the Am-enam/Kpono field off Nigeria onstream, an event that will move the company's operations in this country up a gear.

Production from the Amenam/Kpono Oil and Gas Export Project (Akogep) will make Total the fourth largest oil and gas producer in Nigeria. The new field facilities, which are integrated with the operations from the company's other producing fields off Nigeria, will serve as a hub for other developments.

The project has many impressive features, though Project Director Pierre Nerguararian is quick to point out that the water depth – 40 m – is not one of them. It calls for $2 billion to recover just under 1 Bboe, of which 580 MMbbl is oil and 56 bcm is gas.

Another $200 million has been spent on building the world's largest floating, storage, and offloading (FSO) barge, FSO Unity, which has 2.4 MMbbl storage capacity.

The project is on schedule for start-up in August. Plateau production of 125,000 b/d of oil and 15 MMcm/d of gas is expected for seven to eight years, while the total production life is put at 25 years. For the first two years, all produced gas will be reinjected; thereafter 8.8 MMcm/d will be exported to be used as feedstock at the Bonny LNG plant.

The project's very competitive development cost has earned Nerguararian the nickname "Mr. Two Dollars a Barrel," one that he accepts quite happily. But he also draws attention to other features of the project, such as high local content, commitment to sustainable development, and licens-ees' efforts to secure benefits for local communities.

Road to discovery

Although there is much to look forward to as Akogep unfolds, Total is keen not to forget the intriguing history of the Amenam discovery.

The company's activities in Nigeria date back to the 1970s, when the first licenses were awarded to Elf Production Nigeria Ltd., still the name of the Nigeria subsidiary following the merger of TotalFina and Elf in the late 1990s. In the mid 1980s, as production from the company's onshore Obagi field was declining, EPNL turned its attention to relinquished offshore acreage that was becoming available.

Interest in offshore exploration had been prompted by the realization that the prolific Delta sands onshore could extend offshore. A key breakthrough was made with the discovery of the Biafra sands play.

In partnership with the Nigerian National Petroleum Corp., EPNL was awarded four licenses in the eastern offshore sector. In 1986-87, it ran an extensive program of 3D seismic acquisition – probably the biggest in the world at that time, according to Jean Bié, who took over as exploration manager in 1988. Its priority was the two licenses containing acreage close to the Edop field discovered by Mobil. These have now been converted to production licenses OML 100 and OML 102. No extension of Edop was initially found, but two smaller fields were discovered – Odudu and Afia – and brought into production in 1992.

The partners then turned their attention to areas with higher risk and reward prospects, including what is now OML 99, which includes acreage from two previously relinquished licenses. Here, the seismic showed an interesting structure that coincided with the boundary between the two former licenses. EPNL could see the whole picture in a way that the two former licensees could not, Bié says.

Potentially, the structure represented a classic structural trap, but it lay very deep, around 4,000 m, beneath a high-pressure zone that would be difficult to drill and where potential reservoirs were not recognized at that stage of exploration. The presence of a strong seismic marker with strange features underlying the potentially hydrocarbon-bearing zone complicated interpretation. This seemed to mark the top of a very high-pressure zone, so it was decided not to drill beyond this point.

The well, Amenam-1, was drilled in 1990. As expected, drilling proved difficult, not least the passage through some 1,500 m of highly pressured shale. But beneath the shale the well found a quite normally pressured reservoir consisting of a huge column of hydrocarbons. Determining the nature of the hydrocarbons was not easy, Bié says. The first shows indicated oil, but subsequent logging suggested gas. The well was drilled further, logged again, and tested. Only then did it become apparent that the hydrocarbons were in a critical phase between liquid and gas, with continuous evolution from top to bottom of the column.

The final surprise emerged when the seismic velocity was tested, and it became apparent that the reservoir lay beneath the strong seismic marker at which drilling had been meant to stop. The fault was at 3,700 m depth, and not 4,000 m as had originally been calculated, Bié says.

Appraising the field proved another arduous task. In fact, it took six appraisal wells and another seven years before reservoir understanding was sufficient to allow formulation of a development plan. The field was also found to extend into the neighboring OML 70 license operated by ExxonMobil, which named its part of the field Kpono. To achieve the most cost-effective form of development, it was necessary to unitize the interests in two licenses – the first time this had happened in Nigeria. Under the agreed unitization, EPNL has 30.4%, NNPC 60%, and ExxonMobil 9.6% in Amenam/ Kpono.

Development challenges

One of the key development challenges is maintaining the original reservoir pressure of 400 bar to prevent oil from converting to gas, hence the decision to reinject all gas during the first two years. When gas export begins in 2005, water injection will replace the exported gas.