The UK Continental Shelf (UKCS) is one of the most mature offshore basins in the world. Achieving optimal recovery from the basin is demanding, but as the anticipated ultimate recovery factor is 46% (1) of oil initially in place, there is still significant opportunity to optimise recovery from the existing oil fields. PILOT, a partnership between the UK Oil and Gas industry and the UK Government, has been re-focussing its efforts on maximising North Sea recovery. There are currently only two Enhanced Oil Recovery (EOR) schemes operational within the UK North Sea. The principal barriers to implementing EOR projects are believed to be (1) incomplete subsurface understanding; (2) supply of secure, low cost injectants; (3) the challenge of implementing EOR retrospectively on a brownfield site; (4) concerns over project economics. The PILOT EOR Work Group was set up in 2012 to co-ordinate industry and government attempts to tackle these challenges. A three phase programme was identified to: (1) systematically screen the UKCS fields for EOR potential; (2) engage industry and look for synergies and collaborative opportunities to progress EOR understanding; (3) where possible, initiate new EOR projects with operators. The UKCS EOR screening exercise confirmed that there is still a significant realistically achievable EOR prize of up to 1 billion barrels of oil. The second phase of work focussed on developing collaborative ways of working to tackle the technical and commercial challenges associated with EOR projects, with particular focus on offshore ‘brownfield’ environments. Three EOR techniques were progressed and high graded on the basis of their prize and do-ability in an offshore environment: (a) Low Salinity Waterflood EOR; (b) Chemical EOR; (c) Miscible Gas Injection. Industry workshops were held for each EOR type and prioritised work programmes were implemented via operator "clusters", facilitated by the PILOT EOR Work Group. Examples of deliverables include (i) generation of a low salinity coreflood protocol to ensure that laboratory studies are performed in a consistent manner; (ii) initiation of a Joint Industry Project and an industry call for proposed facilities solutions for implementing low salinity on brownfield platforms; (iii) identification of industry resource to support UKCS operators with planning of chemical EOR opportunities. Successful completion of these collaborative activities will increase the chance of implementing further EOR schemes in the UKCS, unlocking the significant EOR prize.

Single-well chemical tracer tests (SWCTT) have proven to be a valuable technique for evaluating Enhanced Oil Recovery (EOR) responses in clastic reservoirs. Development of carbonate waterflood EOR technologies are relatively immature in comparison, but the use of SWCTT for providing evidential basis in the field promises to be quick and relatively inexpensive compared with inter-well trials. SWCTTs measure the remaining oil saturation (Sor) to waterflood at a 15-20 feet distance from the wellbore. The technique indirectly measures the Sor by analysing back-produced fluids for partitioning tracers in a well which is producing at 100% water cut. Completing the test pre- and post-EOR treatment quantifies the EOR benefit, at least in that near-well region. Laboratory studies suggest that the use of ionically designed waters for EOR in carbonate reservoirs is temperature sensitive. This makes the design of a single-well test complex as it is essential to understand the thermal behavior of the well and the near-wellbore reservoir during any sequence of SWCTTs. Commercial simulators were used to investigate the thermal characteristics of the well and the near-wellbore reservoir respectively. These simulation results were also benchmarked against a water injection trial in another analogous well. The results showed that to ensure the temperature in the near-well region is kept sufficiently high to trigger an EOR response, it is necessary to pre-heat the injection water to >100°C. This is a complex operation especially offshore where the technical and HSE considerations need to be integrated into a sufficiently-sized heating system where space may be limited. Artificial lifting of produced fluids from a well which is producing at 100% water is also problematic offshore. Benefits and drawbacks of various lift options will be reviewed. The effect that delays during the production phase can have on the quality of data from the SWCTT will be shown as well as the options considered to reduce the likelihood of such problems occurring. The need to test this EOR technique in a controlled manner places stringent requirements on the surface facilities to deliver a test within the design specification. The need for low salinity water injection led to the selection of an integrated water treatment system able to produce desalinated water on-demand. This paper is the first of a series of papers aimed at describing the development of an ionically designed waterflood EOR technology for a giant carbonate oil field.