Challenges of Gas Development: Soku Field Oil Rim Reservoirs

Abstract

Abstract The Nigerian LNG Project at Bonny is undergoing significant expansion from it's current 3 trains to 5 trains by the end of 2005. Shell's share of the additional gas demand is met by gas offtake from the Soku oil rim reservoirs. The challenge in Soku is to manage gas offtake between reservoirs to secure optimal hydrocarbon recovery from the oil rims under concurrent production of both gas caps and oil rims. This paper addresses the methods used to establish the sensitivity of oil rim recovery to reservoir uncertainties and development strategy. It shows how an idealised box model, preconditioned to match historic production in reservoirs, is used to guide development plans which are later validated in full 3D reservoir simulation models. The box models and full field simulation have been used to confirm that concurrent production of oil rims and gas caps from Soku oil rim reservoirs can be achieved while optimising oil recovery from the rims. Introduction As Nigeria makes it's transition from oil to oil and gas based economy, the Nigerian Liquefied Natural Gas (NLNG) project, which first came on stream in 1999, is expanding from its current 3 trains with a feed gas requirement of 1477 MMscf/d to 5 trains by end of 2005, requiring an additional 1332 MMscf/d of feed gas. At present, the SPDC share of gas supply is met by an associated gas gathering network covering multiple fields and free gas production primarily from 2 fields - Bonny and Soku. Production priority is given to the richer associated gas streams, followed by Soku free gas and finally Bonny non-associated gas (NAG), which contains dry gas and is used as a swing producer. The current plan is to supply SPDC's share of feed gas for NLNG trains 4 and 5 (T4/T5) from the Gbaran/Ubie development project, involving expansion of the associated gas gathering network and new development of free gas reservoirs (i.e. NAG reservoirs). However, in the short term, Soku field will be required for T4/T5 start-up in 2005 and will be the main supplier to NLNG for between 2 to 3 years, when Gbaran is expected to come on stream. Soku gas well capacity of 1000 MMscf/d will be required for high offtake in the short term. Once Gbaran is onstream Soku will become a back-up (swing) supplier at an annual rate of 250 MMscf/d.