enhanced oil recovery floods basin with potential

Successful enhanced oil recovery (EOR) has the potential to increase production, extend field life, stimulate field redevelopments and defer decommissioning activities – and therefore play a significant role in helping maximise the economic recovery of oil and gas reserves from the United Kingdom Continental Shelf (UKCS).

A number of North Sea operators, including Chevron Upstream Europe (CUE), are currently engaged in EOR pilot projects in the basin to help stem production decline and maximise recovery from existing assets. One of the most advanced polymerised water injection projects in the region is CUE’s Captain EOR project. Richard Hinkley, general manager for Projects and Future Growth at the business unit (BU), recently spoke to Offshore Engineer about CUE’s long-term EOR project at Captain and shared his views on the impact its implementation could have to the field and others in the U.K. North Sea.

The billion barrel Captain Field achieved first production in March 1997 and is being given a new lease of life through Enhanced Oil Recovery.

Advanced Enhanced Oil Recovery (EOR) technology allows Chevron to extend life from existing assets, such as the Captain field in the U.K. North Sea.

“We have been working on the Captain EOR project for 10 years. Earlier this year, we started our fourth pilot project on the field to further refine our future polymer EOR plans. Set to be a staged roll-out, starting with around six long-reach horizontal polymer injection wells, performance will be carefully monitored and assessed to determine the future potential for a full-field expansion.”

Discovered in 1977, in Block 13/22a, the billion barrel Captain Field achieved first production in March 1997 – 20 years ago this year – thanks to technology developments in horizontal drilling and down-hole pumps.

“For many years, the Captain Field has been under water flood, which means a lot of effort has, and still is, put into water production and treatment, with some 300,000 barrels of water produced daily. However, there is still a lot of bypassed oil, because of the way water flood results in a “coning” effect in the reservoir.”

As Richard explains, Captain’s reservoir conditions – including the pressure, temperature, type of rock and oil properties – make it an attractive candidate for polymerised water injection.

“By introducing polymerised water, we can exploit the mobility ratios between the oil and the polymer. Instead of coning, we are bull heading a bank [of polymerised water] towards the producing wells.

“The timing is important,” says Richard. “There is a tradeoff between not leaving it too late and not going too early when you still have an effective water flood.”

To assess the potential for polymer EOR and develop its approach, CUE started with a screening process, which was followed by lab trials, before going on to complete three pilot projects. Each pilot has targeted specific uncertainties.

The first, an injector-producer pair, in 2010, ran for 30-months and was undertaken to assess whether the polymer enhanced recovery process worked at Captain. The second, an injector producing to four wells, drilled in 2013, ran for 18-months, and helped inform the BU whether polymer worked on a typical producer-injector configuration. The third pilot, which commenced last year (2016), enhanced CUE’s understanding of the logistics and supply chain requirements involved in polymer EOR at Captain.

Building upon these efforts, in the first quarter of this year CUE commenced injection into a fourth well, which is currently ongoing and will further expand the BU’s learnings from earlier pilots.

“As we move forward, we are fine-tuning the polymer and continually learning. Each pilot informs the next phase and helps us progress the project,” adds Richard.

Crucial to the work to date has been designing a polymer for the specific conditions at the Captain Field. As well as developing the right polymer, CUE is also keen to develop a strong supply chain for polymer.

“One of the key lessons is that it takes a lot longer than you think,” explains Richard. “There are no short-cuts. We have been 10-years from initial screening and as a result we are on pilot number four. We have demonstrated the polymer works. We have had to fine tune the polymer for the specific reservoir conditions at Captain.

“Now we are at the point where we are looking at long-term staging of the development, going from a pilot to six wells in the platform area [Area A] of the field. We are all currently focused on moving towards a final investment decision (FID) for this first phase of the project later this year. If that is a success, in time the hope would be to go to a full field expansion.”

Polymer injection facilities were installed as part of the original Captain development but some brownfield work is needed to accommodate the first phase (six-well) of the project. This will include bulk provision of the polymer and modification work on the Captain Wellhead Protector Platform, including new polymer mixing equipment to expand the field’s current processing capacity.

CUE’s learnings from the project, along with lessons learned from others in the basin like Statoil’s Mariner Field and BP’s Schiehallion Field, are to be included in a project led by the Oil and Gas Authority (OGA) to create a “starter-pack” for those looking to try polymer EOR.

“We are committed to sharing our experience and knowledge around EOR, and we are working closely with the OGA to ensure this will be incorporated into the ‘pack’ for industry. This will help other operators in the region understand if EOR is suitable for their reservoirs and what expectations they can have towards implementation and supporting the goal of maximising the economic recovery."