Effect of salt on the performance of drag reducers in slickwater fracturing fluids

Slickwater fracturing has historically utilized freshwater as a base fluid and Friction Reducer (FR) as a main additive to reduce the friction pressures in the wellbore and within the fractures. This technology is getting challenging because of the limited sources of freshwater, the increased flowback fluid disposal costs, and stricter disposal regulations. The oil and gas industry has been trying to optimize the reuse of slickwater fracturing flowback fluids to help reduce the use of freshwater. The flowback contains mainly water, salts from formation water, and chemicals that were introduced from the hydraulic fracturing. The main objective of this study is to experimentally investigate effects of salinity on the performance of FRs for the purpose of reusing the flowback. The Hydraulic Testing Facility was used to perform hydraulic tests to investigate the effects of salinity on the performance of FRs. Three commercial FRs, namely anionic Friction Reducer A (FR-A), anionic Friction Reducer B (FR-B), and cationic Friction Reducer C (FR-C), were used to conduct the tests. The concentration of the FRs was varied from 0.5 to 1.2 liters/m(3) of water (0.5-1.2 gallons per thousand gallons of water). Sodium Chloride and Calcium Chloride at different concentrations were added to the solution to study the salinity effects. In addition, multiple rheological tests were executed to understand the effects of salinity on the rheological properties of slickwater. The results revealed that the anionic FR-B performs better than the anionic FR-A in fresh water. The percent friction reduction of FR-B and FR-A at 0.478 g/L (4 pptg) in fresh water were about 60% and 40%, respectively. In addition, the performance of FR-B is less sensitive to salts than that of FR-A. Therefore, It is recommended to add 0.478 g/L (4-pptg) of FR-B directly into the flowback, which has the total dissolved solid values of 100000 mg/L or less without the need of pretreatment to achieve the percent friction reduction of 40% or higher. Cationic FR-C performed the best when compared with anionic FR-A and FRB at high salinity, e.g. 200000-mg/L total dissolved solid. Under the testing conditions, a conservative conclusion may be drawn that cationic FRs may perform better with the presence of salts than that of anionic FRs.