SWCTTs are often used to assess residual oil saturation (Sor) or remaining oil saturation (ROS) in the near well-bore region before initiating enhanced oil recovery (EOR) or improved oil recovery (IOR) projects. The technique is based on the chromatographic separation of two different tracers. One oil/water partitioning tracer partly hydrolyzes in the reservoir, to generate a secondary non-partitioning water tracer. Most of the reported SWCTT operations typically use ethyl acetate (EtAc) as the primary tracer. Some of the challenges with the current set of chemicals used are their high flammability, poor detection limit (ppm range) and the large quantity required.
A new set of tracers has been developed to overcome these challenges. These were pilot tested in a giant carbonate reservoir undergoing peripheral water-flood to measure Sor prior to a field redevelopment project. The new tracers were field tested concurrently with the conventional EtAc method for comparison purposes. About 100 g (0.1 kg) of each of the new tracers were injected at different times and different ways during the conventional SWCTT operation. It is worth highlighting that tens or hundreds of kilograms of conventional SWCTT tracer are needed for a single operation.
This paper reviews the complete design and implementation of the test, operational issues, the analyses and the interpretation of the results. The Sor measured by each of the novel tracers compare well to that from a conventional SWCTT. The results also show that these tracers can be injected in pulse mode – at a very short time interval, thus reducing the operational time needed for pumping the chemicals. In addition, the test results suggest that several tracers with different partitioning coefficient may be deployed to investigate different depths of the reservoir.
The pilot further demonstrate that many tracers with different properties may be deployed simultaneously without risking interference with the Sor measured during the test – this may revolutionize measurements of saturations in SWCTT operations.