Understanding Flow Through Interwell Tracers

This paper presents the successful implementation of an interwell tracer program performed in a multilayered reservoir with mature waterflooding. The objectives of the program are to evaluate water channeling in a high water cut field and, assess sweep efficiency improvements in an EOR pilot test. An extensive methodology was prepared to ensure the quality of the program. The first stage followed the screening of areas and reservoir layers with underperforming waterflooding. After that, the design stage included a selection of tracer available in the market, volume calculation and breakthrough time simulations. The execution plan defined the optimum injection rates, equipment and lab tests requirements for the monitoring and field sampling schedule. The results were being recorded in a monthly progress report and analyzed by a technical team in charge of the project. Interwell tracers made possible to confirm water channeling issues and provided information about the severity of preferential flow using the breakthrough times obtained for each reservoir layer. It was also possible to observe how changes in injection rate impacted the recovery of the tracers, creating different flow patterns at different flow rates. The six-month monitoring ended with the estimation of channel volume to design water conformance treatments. In addition, the findings from the interwell tracer conducted in the EOR pilot test showed an increase in the breakthrough time after three years of polymer flooding and, a change in flow patterns that allowed the displacement of previously bypassed oil. These results are interpreted as a measurable improvement of sweep efficiency and served as input to appraise the performance of the pilot test.