Water used to make fracturing fluids usually requires treatment to reduce aerobic acid-producing bacteria and, more importantly, to eliminate anaerobic sulfate-reducing bacteria that can cause a well to go sour. Typically, this treatment is performed with the use of chemical biocides. To reduce the amount of chemical biocides used, a new technology, ultra-violet (UV) light, was tested. The equipment used to generate sufficient UV light to disinfect the large volumes of water needed for fracturing was mounted on a trailer for road mobility (Fig 1). This required modifying the UV light equipment and the way it was installed to withstand oilfield conditions. The effectiveness of UV light in disinfecting water for a fracturing treatment was tested in both a controlled laboratory environment and also on a fracturing location. Serial-dilution tests were performed to examine the effectiveness of UV light in controlling both aerobic- and sulfate-reducing bacteria. The serial-dilution method was chosen because it measures both active bacteria and dormant spores that can become active when placed in ideal conditions.

Bacteria control has recently become an important topic for discussion among the oil and gas industry, although it is still misunderstood by the industry. A bacteria problem can oftentimes be subtle and difficult to detect. Bacteria detection in the field is difficult because many tests take a long period of time or are simply not accurate. New regulations on flowback and produced water have led to investigating ways to reduce the amount of residual chemicals in flowback fluids. Environmental concerns associated with chemical disinfection have led to the move from traditional chemical disinfection to mechanical procedures (Cho 2002). Using UV light to disinfect water on-the-fly for stimulation treatments will greatly reduce the amount of chemical biocides that are necessary. A low concentration of biocide is still recommended to provide a more long-term protection from bacteria as the fluid is pumped through the blender and then downhole. Although the use of some biocide is still recommended, these small concentrations are more likely to be at undetectable levels in flowback waters.

You can access this article if you purchase or spend a download.