Successful Breaker Optimization for Polyacrylamide Friction Reducers Used in Slickwater Fracturing

Abstract

Abstract To pump a high-rate fracture stimulation with fresh water or brines, a friction reducer must be employed. Most friction reducers used in slickwater fracture stimulation are high-molecular-weight polyacrylamide emulsions. Since these friction reducers are typically pumped at low concentrations (0.5 to 2 gpt), the industry belief has been that these polymers are causing minimal damage to the formation. There has also been a perception that the polyacrylamide polymer is difficult to degrade. However, fracture stimulations in areas such as the Barnett Shale use very large quantities of water with several stages per well which introduces large volumes of friction reducer into the formation. Because these large treatments are now widely used, several production companies have recently expressed concerns about the possible fracture and formation damage caused by these friction reducers. For this reason, a study was undertaken to find suitable breakers to effectively reduce the size (or molecular weight) of the polyacrylamide polymer chains and, therefore, reduce fracture and formation damage. Several conventional oxidizers were chosen and screened to determine if they could effectively reduce the viscosity of the polyacrylamide polymer. The molecular weight degradation of the polymer was then measured using a molecular weight cut-off (MWCO) filtration technique to determine the size and percentage of polymer fragments. Surprisingly, most of the breakers tested showed some reduction in viscosity and in molecular weight. Additional laboratory testing was then conducted to ensure that the addition of breaker to the friction reducer did not adversely affect polymer hydration or friction-reduction performance. This study reports on the results of the testing and shows which breakers were most effective in reducing the molecular weight of the polyacrylamide polymers used as slickwater friction reducers.