Waterflood Conformance Improvement Method in Naturally Fractured Carbonate Reservoirs with Gel Injection

The workflow for waterflood conformance improvement in a naturally fractured carbonate reservoir with polymer gel injection is presented. The workflow outlines a systematic way of identifying the conformance candidates and evaluating optimal gel volume for the job design predicated on using the regular surveillance data as well as a novel way of gel characterization with lab measurements. Economic and technical success of conformance jobs is based on successful implementation of the improved workflow demonstrated in this work. The wells in the carbonate reservoir of interest are screened for conformance issues using only the injection and production data. Using a set of Chevron analytical tools with the field injection and production data, we screened over four hundred wells and selected four candidate injectors with the most severe water cycling issue in the carbonate reservoir of interest. Inter well tracer test was part of the pilot to assess the effectiveness of the workflow by verifying the correct candidate selection and designed gel volumes by quantifying the thief zone volumes. Lab extrusion tests of selected mature polymer gels also demonstrated that the flow capacity of an open fracture could be reduced up to 4000 times even after ruptured by continuous water injection at the right concentrations. After the tracer tests confirmed the severe conformance issues for the selected injectors, conformance treatment was designed for optimum concentration using the lab results and optimal volume using the tracer interpretation. Finally, the first gel injection pilot is executed, and appropriate surveillance plan implemented to evaluate the results. During pilot execution injection pressure, polymer concentration and volumes were closely monitored. The offset producers were tested frequently as part of the surveillance plan. The analysis of the injection and production data shows positive response with more oil production for each barrel of water injection in all four treated patterns. This work exhibits a systematic approach of polymer gel injection for waterflood conformance improvement from candidate selection to lab tests for selection of the most appropriate chemical agent to field execution. The objective of this work was to establish criteria for more efficient and economic gel conformance treatments with high success rate in the carbonate field of interest.