Sustainable development relies on biocide usage reduction

Operators across the oil and gas industry are using recently developed technology to greatly reduce the need to use biocides in fracturing fluid. Using chemical biocides to control bacteria growth in fracturing fluids has been the traditional approach.

Water used in fracturing fluids must be treated to reduce the concentration of bacteria since excessive bacteria can lead to the corrosion of iron or steel, cause the well to start producing sour (HS) fluids, and destroy the fracturing fluid by causing it to become too thin to create geometry and carry proppant. The chemical biocides typically used are toxic chemicals that must be handled carefully and registered with federal and local environmental protection agencies. Additionally, biocides can interfere with chemical additives in the fracturing fluid and cause equipment damage.

Using UV light disinfection is enabling operators to reduce biocide use from 0.5 gal/1,000 gal of fluid to 0.25 or even 0.1 gal/1,000 gal of fluid, resulting in an 80% reduction in biocide volume required. In some cases, the UV disinfection process can totally replace chemical biocides and eliminate the need for tens of thousands of gallons of biocide used per frac crew per year. Obviously, this reduction in volume reduces the HSE exposure related to transportation and handling of biocides for both the service provider and the well operator.

The treating unit includes a UV light system packaged to be mobile, standalone, and suited for the rugged oil-field environment. The treatment trailer is designed to be compatible with existing fracturing blending equipment so that no equipment modification is necessary to place the UV unit in a fracturing rigup. During the fracturing operation, the UV treatment trailer is rigged between the frac tanks and the fracturing blender. The suction pump on the blender draws water from the frac tanks and through the UV treatment unit, where it is disinfected. Microbiology testing is routinely done to determine the level of bacteria in the water and also the effectiveness of the ultraviolet light disinfection.

In 2011, this technology eliminated more than 250,000 gal of biocide that would have been handled by site personnel and then pumped downhole. The combination of net benefits to the industry resulted in the technology being awarded Hart Energy’s Meritorious Engineering Achievement award in 2012; however, the real winners are the environment and the operators who choose to use the technology.

UV light has been used successfully for many years in several industries, including pharmaceutical, hospital, and food and beverage as well as municipal drinking water applications. There are basically three classes of UV light: UVA, UVB, and UVC, with UVC being the wavelength that is aligned with controlling microbial populations. When a microbe comes into contact with a UVC wavelength, the microbe is not killed, but the microbe’s DNA is rendered incapable of reproduction.

Understanding biocides

Twelve tests showed the UV light process to be highly effective controlling bacteria growth.

Traditional biocides come in basically two categories, oxidizers and nonoxidizers. Oxidizers are not discriminatory toward the microbes that they eliminate. These oxidize anything that is contacted in the solution. This includes the many species of microbes found in frac fluids as well as the actual frac fluid components themselves, which can lead to fluid formulation issues.

Nonoxiders are much more selective as to which organisms are impacted as these have varying mechanisms that make them effective. Some nonoxidizers enter the cell wall and impact basic cellular metabolism. Others simply digest the cell wall, causing the cell to die as a result of a lack of cellular integrity (among other effects). While some have “broad spectrum” capabilities, most are fairly species-dependent when applied correctly.

The UV treating unit works seamlessly with existing fracturing equipment.

To apply nonoxidizers correctly, a toxicant evaluation of the type of microbes to remove should occur given the specific serial nature of most nonoxidizers; however, given the many complexities in completion operations, obtaining a representative sample for a toxicant evaluation is not always done effectively, if at all. The result is a less than desirable, inefficient process that is not beneficial to the environmental improvements required by the oil and gas industry. Also, many nonoxidizers are limited by a narrow pH range in which they are effective, further contributing to inefficiency.

With the challenges inherent with using biocides in the oil field, operators have been extremely satisfied with UV light control methods. The UV process does have some technical limitations. But regardless of the species, any microbe will be unable to reproduce when it comes in contact with UV light. Conversely, if the microbe is not exposed to the light, the process will not be effective. Exposure to the light is a function of transmittance or the ability of the UV light to pass through the water and come into contact with the microbes in the water. A high total suspended solid concentration or high turbidity in the water can prevent UV light from contacting the microbes. But, with quality transmittance, effective microbial control is accomplished with UV light.

Significant engineering effort was required to ruggedize the UV light chambers for oilfield use. A special wiper assembly keeps the bulbs clean to help improve effectiveness of the system.

Halliburton’s UV light system is the CleanStream service. The system is capable of treating up to 100 bbl/min flow rate. The standard location in a fracturing spread is for a CleanStream service unit to be placed just prior to the blender. This enables all of the water that is to be pumped downhole to be treated with the UV technology. Other applications include side stream treatment for frac ponds, offshore platforms, mature field applications such as water and polymer flood, and any area in the oil field where microbes tend to congregate and biocides are being applied.

An extra benefit in applying the service is that the majority of operators who use this technology have not only realized the net environmental and safety benefits but economic benefits as well. UV light disinfection as encompassed in the CleanStream service technology has been proven to help operators eliminate biocide handling and reduce the quantity of biocide pumped downhole while saving money and further promoting sustainable development practices in the industry.