Treatment of High Salinity Oilfield Waters Through Evaporative Cooling: Proof of Concept and Feasibility Examination

Abstract

Abstract In this research, we aimed to evaluate the effectiveness of evaporative cooling (EC), a novel method, in reducing Total Dissolved Solids (TDS) in produced water from hydraulic fracturing activities in the Permian Basin. To investigate the potential of EC for TDS removal in oil field waters, we conducted experiments using a lab-scale EC system consisting of three cooling pads (filters), a fan, a water reserve, and a pump. The reserve water, representing the initial untreated produced water, was continuously circulated and wetted the pads. Inlet and outlet temperatures, relative humidity, and the remaining water volume were monitored using a temperature humidity meter. Control experiments were performed using different volumes of distilled water (2, 3, and 4 gallons) to examine the impact of initial water volume in the reserve on the efficiency of the EC system. Additionally, control experiments were conducted with a fixed reserve water volume, but varying salinities were achieved by adding NaCl to distilled water (ranging from 0 to 70,000 ppm) to evaluate the effect of salinity on evaporative cooling performance. Furthermore, three experiments were conducted using real produced water samples from the Northern and Southern Midland regions of the Permian Basin, characterized by high salinity and additional impurities due to oil and gas production. Energy consumption was compared to regular thermal evaporation using an electricity usage monitor. The results clearly demonstrated that variations in reserve volume had a substantial impact on the system's efficiency, with a notable threshold observed at 2 gallons (0.3 bbl/day/EC system). Above this threshold, the system efficiency experienced a significant decline. In synthetic brine experiments, a slight decrease in system efficiency was observed with increasing salinity. The threshold salinity for maximizing TDS removal was found to be approximately 35,000 ppm, equivalent to the TDS content of seawater, resulting in over 80% TDS removal. For real produced water samples, evaporative cooling led to reserve volume reductions of 50% and 35% in the Northern Midland (E9) and Southern Midland (E10) regions, respectively, within the same experimental duration. The maximum TDS removal observed in the treated water was 45%. Deviations in EC efficiency between synthetic brines and real oil-field brines were attributed to the presence of additional contaminants in the real reservoir brines. Nevertheless, TDS removal efficiencies remained significant for the real produced water samples. Moreover, evaporative cooling demonstrated significantly lower energy intensity compared to regular thermal evaporation. This study provides valuable insights into the potential use of evaporative cooling as a treatment method for high-TDS oil field waters, which is relatively unexplored in existing literature. It offers new perspectives on the effectiveness and sustainability of evaporative cooling in treating high TDS-salinity oil field waters. These findings have significant implications for the petroleum industry, and the applicability of EC may extend to other industries as well.