Design, Implementation and Results of an Inter-well Chemical Water Tracers Pilot Test to Improve Water Flood in Complex Reservoirs

The use of water tracers to better understand and improve water flood performance has long been part of the reservoir management toolbox. Its use is even more relevant when applied to complex and heterogeneous reservoirs. This paper describes the planning and implementation phases of a chemical tracer injection pilot in the Al Shaheen oil field, offshore Qatar. In Al Shaheen injection water has historically been used as natural tracer to identify inter-well communication in the field by analysis of the salt and ionic content of produced water. However, this approach has become less effective over time. Identification of short-circuits is getting more complex with the increasing number of wells completed. A tracer pilot including chemical water tracers was designed to identify inter-well communication and flow paths of injected water in a complex area of the field. The geology of this area is highly heterogeneous, with a stacked sequence of carbonate and clastic reservoirs. Numerous features were identified as the possible cause of these inter-well communication paths, including faults and fractures, thief zones, permeable shale and/or absence of shale. The pilot includes two water injection wells completed in two different reservoirs and twenty six oil production wells. This paper reviews the selection of the candidate wells, the operational constraints as well as the detailed analysis and interpretation of the results. Based on this pilot, interwell connection has been proven in most of the area of interest. Tracers have been detected in six of the twenty six wells, with breakthrough times ranging from three to seventy days. Communication between the carbonate and clastic reservoirs was confirmed in two wells. For some of the early samples, anomalous results were obtained. This has been attributed to contamination during sampling at the platform, and was remediated by improving the quality control during sampling. This water tracer pilot paves the way for further application across the field. Ultimately the tracer results will be used in combination with other surveillance techniques to identify by-passed oil and design fitfor-purpose solutions to target higher recovery.