Effect of Dissolved Solids on Reuse of Produced Water in Hydraulic Fracturing Jobs

Abstract

AbstractMultiple-stage hydraulic fracturing jobs are usually needed to produce economically from tight sand gas reservoirs. High costs of water acquisition and waste water disposal, and the lack of available water resources near operation sites, make the reuse of produced water an unavoidable option. Applications of produced water in hydraulic fracturing jobs result in low quality fracturing fluids, which usually have high levels of hardness and salinity. This is especially true for flowback fluids, which contain high polymer loading. The viscosity and rheological properties of fracturing fluid, significantly affect leak-off rate, proppant placement, length and width of fractures, fracture conductivity, and consequently, the success of the treatment. The objective of this study is to determine the acceptable dissolved solid contents for flowback fluids to prepare fracturing fluids.Analyses of 36 flowback fluid samples from the West Texas region have been collected, and experimental studies were conducted on the analysis of the dissolved solid contents of produced water, which affect the application of flowback fluids and the capability of prepared fluids in proppant transport and handling. A high-pH borate crosslinked guar-based polymer has been picked to determine the ranges of acceptable salt contents. Dynamic viscosity and rheology tests, static proppant settling, and small-amplitude oscillation rheology, were the methods used to evaluate prepared samples at room temperature and medium temperature (225°F).The results show that some divalent cations such as calcium and magnesium have severe negative effects on the prepared polymers. Calcium is the controlling ion and about 60% of flowback fluids need to be treated to meet the maximum acceptable concentration criteria for these ions. Although monovalent cations such as sodium and potassium were tolerable at higher concentrations and the potassium contents in almost all flowback fluids meet the determined acceptable value, more than 70% of samples need to be treated for high sodium ion concentration. Although the presence of other ions like iron, show no significant variation in fracturing fluid properties, they can affect treatment jobs in special cases. The results comply with the extracted outcomes in SPE 168614 and show that adjusting the concentration of the polymer, buffer, and crosslinker can minimize the effect of temperature and salts. The fluids prepared with the determined ranges of dissolved solids showed reasonable rheological stability and proppant transport characteristics. This paper introduces the practical operating range for produced water content and defines the factors that can adversely impact borate-crosslinked fracturing fluid characteristics at low and medium temperature applications.