The Issue: Frac Water Reuse
The Solution: Treatment with ClO2
A Mid Continent Oil producer was experiencing disinfection and permitting difficulties using conventional Oilfield biocides. High bacterial loading and short contact times required the use of high dosages of conventional biocides that were both costly and of concern to the regulatory community.
Chlorine Dioxide Application Considerations
Chlorine dioxide is an oxidizing biocide that has been used for municipal water disinfection in the United States since the 1940's. It is also used in the food industry as a direct food contact and incidental food additive status sanitizer and disinfectant for the vegetable, meat, dairy, and fresh pack sectors. The benefits for the use of chlorine dioxide in these industries are that chlorine dioxide provides superior penetration into biomass combined with superior microbial kill, while also preventing the formation of undesirable disinfection by-products such as THM's (from chlorine or bleach) and bromates (from ozone or hydrogen peroxide). Based on the company's experience with chlorine dioxide in these and other industries, Sabre developed a treatment approach.
Chlorine Dioxide Treatment Approach
Sabre's DiKlorSM service, using chlorine dioxide, was applied to the water to be used for well fracturing in much the same way as it would be for primary disinfection of municipal drinking water, or for pre-treatment of potable water aquifer injection wells. A Sabre portable DiKlot™ generation system with a maximum capacity of 24,000 lbs. per day continuous production was set up on the location. This system has nearly infinite turn-down capability due to the incorporated dosage pump system that can feed four points independently at rates from 0.02 to 2.5 lbs. chlorine dioxide per minute each. Chlorine dioxide dosage rates and residual values are monitored within the control cabin of the unit. Water was pumped from a small reservoir that contained some agricultural run-off to a series of frac tanks set up on location at a rate of 110 bbl per minute. Prior to start up, the chlorine dioxide demand of the water was determined and the water was tested for sulfate reducing (SRB) and general aerobic bacteria (GAB). The demand was found to range from 12 to 15 mg/l and SRB and GAB levels were found to be 105 and 104 cfu/ml, respectively. Chlorine dioxide was added at such a rate as to achieve a residual of 0.5 to 1 mg/l. Residual was monitored on 15-minute intervals throughout the stage. Residence time for the chlorine dioxide treated water in the frac tanks was approximately 15 minutes. Analysis was also performed on grab samples of the treated water for SRBs and GABs.
Chlorine dioxide residuals were maintained throughout the process between 0.4 and 0.9 mg/l. There was no growth on SRB and GAB samples collected throughout the process. Reports from the producer have indicated significantly less occurrence of hydrogen sulfide production from wells fractured with chlorine dioxide-treated water than those treated with conventional biocides-while over 50% of the conventional biocide-treated wells experienced hydrogen sulfide production within 12 months, no chlorine dioxide-treated wells reported hydrogen sulfide production within 12 months of fracturing.
The Science of Success
Unlike alternative technologies, chlorine dioxide is a true gas that is a relatively stable oxidant, reacting only with reduced compounds such as sulfides, phenols, and biomass. Additionally, chlorine dioxide kills both active and inactive bacteria, unlike conventional biocides. Chlorine dioxide has also been shown to kill bacterial spores with relatively low contact times, and bacteria cannot build resistance to chlorine dioxide, unlike conventional biocides. As it is a well-established EPA-registered biocide for use in drinking water and food, regulatory considerations are limited to local permitting requirements.
Over their 10-plus year use history in the petroleum industry, Sabre chlorine dioxide systems have a perfect safety record. This is due to their inherent functionality, where chemical precursors are vacuum fed to the point of reaction to form chlorine dioxide in the absence of dilution. This formation of chlorine dioxide independent of the water stream allows Sabre systems to operate on any fluid, including oil, water, emulsions, and slurries. This unique chlorine dioxide system has been patented by Sabre.
Chemical precursors on portable Sabre chlorine dioxide systems are separated by secondary steel containment to further protect from accidental mixing. Sabre has a unique understanding of the health and safety issues related to the use of chlorine dioxide due to its extensive experience with the application of chlorine dioxide in both gas and solution phase.
Chlorine dioxide is now used in many states for the disinfection of fracturing water and fluids, eliminating hydrogen sulfide and reducing treatment costs and environmental and safety concerns.