As waterflooding has become one of the most favorable approach for secondary recovery globally, understanding flood front behavior and reservoir sweep becomes even more pertinent to maximize recovery. To monitor the effectiveness of a waterflood program, chemical tracers are often deployed for enhancing surveillance techniques. This paper presents a classic example of value creation from the existing tracer database with the demonstrated workflow of the Residence Time Distribution (RTD) method in tracer interpretation applied in a mature waterflood field. The analytical study conducted was in a complex oil rim field located in East Malaysia.
As a five-year sampling programme was initiated for this field, a substantial amount of sample and corresponding tracer response data allowed the field to be a strong candidate for tracer RTD data analysis. Injection was carried out via smart wells into 28 zones and samples were taken on routine basis from monitored producers. Breakthrough of unique tracers coupled with low detection levels from the vendor laboratory were utilized as a foundation for constant waterflood optimization. Flow geometries and reservoir continuity between each injector-producer pairing were measured in detail through analysis of chemical tracer response curves.
Apart from immediate injector-producer communication upon first tracer breakthrough, a detailed study on water flood performance based on the RTD method allowed the pore volume swept, mass recovered from each section and quantification of heterogeneity to be determined. Flow geometry and reservoir continuity between each injector-producer pairing were also measured allowing identification of thief zones, out of zone injections, vertical communication between layers, and behind casing flow. As a result, the information gathered allowed the optimization of each injection zone based on the outcome of the tracer response at the respective producers. This information has proven beneficial to the reservoir surveillance team allowing insightful decisions to be made upon subsequent opportunities for production and water flood optimization.