what does 'departure' mean in drilling depth context? see last paragraph below.
The Akpo challenge
Total says its experience of Gulf of Guinea conditions led up to the Akpo challenge. "Because we have been working in Nigeria since 1962 and operating several large projects we were more than ready to develop a deep-water project, combining our technical expertise gathered in, for instance, Angola, our knowledge of Nigeria and our geoscience expertise."
Total's initial concept for the development was for full gas injection, because studies indicated that a small pressure-drop would cause the reservoir fluid to separate out and jeopardise the recovery of condensate. But this concept evolved into a hybrid scheme, with some gas injected and some landed to Nigeria LNG's gas-liquefaction complex at Bonny, to capture some sales revenue from the gas. The firm says further studies of the reservoir showed, surprisingly, that the reduced injection rate would actually increase the recovery of liquids.
The reservoir will be managed by controlling the gas-to-liquids ratio in the wells, with the condensate plateau maximised by producing from low gas-to-liquids parts of the reservoir first and by controlling the arrival of water in the wells. For pressure maintenance, a large number of water-injection wells will be needed from the start of production – there will be 20 and two more for gas-injection.
The production architecture consists of 22 wells, all pre-drilled and all with 3-D trajectories – there are J-shapes and S-shapes and horizontals with departures of up to 3,000 metres. Total will not answer questions about Akpo costings, but it is clear that the drilling programme will account for a large part of the capital expenditure.
