Water used in fracturing fluids must typically be treated to reduce the concentration of aerobic acid producing bacteria and, more importantly, anaerobic sulfate-reducing bacteria that can cause a well to go sour. Typically chemical biocides are used to provide the disinfection. However, biocides can interfere with chemical additives in the fracturing fluid and cause equipment damage. Additionally, biocides are toxic chemicals that must be handled carefully and registered with federal and local environmental protection agencies. Some areas strictly regulate which chemicals can be persistent in treatment liquids flowed back from wells. To address the issues associated with the chemical biocides, disinfection via ultraviolet (UV) light has been introduced into hydraulic fracturing operations. The use of UV light can greatly reduce the volume of chemical biocides used and also decreases the biocide concentration in liquids flowed back from a treated well.
Early UV equipment treated water as it was placed into storage tanks on the fracturing location. This allowed for possible recontamination from biofilms present in the storage tanks. A new trailer has been placed into operation that treats the water on the fly as it flows from the storage tanks to the fracturing blender. The performance of the UV light equipment has also been improved. The disinfection effectiveness of the UV light system has been verified on site during fracturing treatments using the serial dilution method to measure aerobic and sulfate-reducing bacteria levels, both before and after the UV treatment. The test results prove that bacteria concentration in the fracturing water can be significantly reduced, sometimes to undetectable levels, by UV treatment.