Slickwater Friction Reducer Performance Evaluation and Application

Abstract Friction reducers (FRs) are a vital component of slickwater fracturing fluids used in hydraulic fracturing operations. FRs, which are typically made up of high molecular weight polyacrylamide-based polymers, help decrease frictional pressure losses and improve the effectiveness of fracturing operations by allowing for higher fracturing (frac) injection rates at the same or lower surface pressures. By optimizing FR selection for field application, cost savings can be realized through reduction in chemical costs, reduction in equipment maintenance frequency, and rental savings. Furthermore, operations could be modified to use more produced water. Evaluating FR performance in the laboratory typically consists of running flow-loop experiments to measure pressure reduction in tubing or pipe over time. However, there is no industry-standard method for evaluating FR performance and different labs have developed their unique protocols and loop designs. To mitigate this deficiency, the project team designed and installed a FR evaluation flow loop and developed a protocol that effectively evaluates FR performance. The team compared performance of various FRs from selected FR suppliers focusing on three attributes: hydration time, maximum pressure reduction, and sustainability of pressure reduction over time. For a given test water, all candidate FRs were tested in the same conditions to allow direct comparison of FR performance. This work showed that pipe size, Reynolds number, and shear rate all affect friction reduction performance; but if testing is done under the same conditions, performance can be compared and ranked directly. Based on comprehensive testing to identify the best performing FRs for brackish, produced, and mixed water blends, a field test with the recommended candidates was conducted in support of a frac-chemical unbundling effort. FRs used in the field test were qualified using the in-house FR evaluation flow loop. Friction reducer performance in the field trial confirmed the FR lab evaluation protocol correctly ranks FR performance and enables scaling to field operation. There were no accepted methods to scale-up lab FR performance to predict field conditions and as accurate models continue to be developed, the main method for evaluating FR performance continues to rely on qualifying FRs based on lab-scale experiments. To bridge the gap, the project team developed an empirically based tool to improve FR selection using a comprehensive test matrix considering FR dosage, water salinity and water hardness. Development of this tool used constant test conditions so that consistent recommendations can be made.