A Design for the Evaluation of a Waterflood EOR Technique by Single-Well Chemical Tracer Test in an Offshore Environment

Abstract

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.