Wireline Spring 2018

It has been a marathon, not a sprint, for those steering a game-changing enhanced oil recovery programme at Chevron’s Captain Field. But the pace has picked up in recent months as the prize looms ever closer. Wireline reports Captain All on board with

MER | Captain Field

T he driving principle of reaching every recoverable drop of oil in the Captain field - 90 miles north-east of Aberdeen in the Outer Moray Firth - has steered the development since it was first planned in the 1990s. Indeed, it is only thanks to the foresight applied back then that today’s enhanced oil recovery (EOR) project is happening at all. “The initial design of the Captain FPSO (floating, production, storage and offloading) vessel had the foresight of integrating storage and pumping facilities suitable for polymer EOR at the onset,” says Chevron business services manager Tony McGarva. “Due to the heavy nature of the Captain Field oil, traditional recovery mechanisms of water injection will leave a lot of oil unrecovered. Injecting a polymer with the water improves the recovery from the field and will maximise economic recovery. There is no doubt our predecessors’ foresight during field design has allowed the EOR field trials to happen.”

Stage 2 – currently in a detailed planning phase – would extend polymer EOR into Captain’s subsea wells. Project manager Colin Freeland explains: “There’s a bit more complexity involved in getting polymerised water to subsea trees rather than ‘dry’ trees, so we’re working on that. There is high value placed on learnings, results and observations from the first phase feeding into the design for Stage 2.” Towards the end of last year, Chevron made the final investment decision to go ahead with phase 1, paving the way for this pioneering application in the North Sea.

Put simply, adding polymer increases the viscosity of the water injected into the heavy oil reservoir. With simple water injection in heavy oil reservoirs, the fluid property contrasts involved results in bypassed oil between injection and production wells. The polymer helps achieve a more even recovery/sweeping process, with oil between wells becoming mobilised that would otherwise have remained unrecovered. Economic recovery A key tenet for success is making sure the project is competitive over the long term and through price cycles. So, a decision was made in 2016 to split Captain EOR into two stages to be sure of its ongoing viability through learnings. Stage 1 is focused on increasing recovery within the existing platform area of the field (known as area A). It requires small-scale topsides facility upgrade work and a drilling programme that gets under way this year encompassing producer and injector wells. Stage 1 culminates in polymer injection into five long-reach horizontal injection wells.

Conventional water injection is supporting recovery of around

30-35 per cent of the estimated one billion barrels of oil originally in place at Captain. The field is likely to see an increase in its yield of between 5 and 7 per cent through Stage 1. >

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