By Devatva Vashishtha, Julie Villalobos and Danny Jimenez
Water management in the oil and gas industry is a complex process, and one that can result in excessive operational costs as well as serious safety concerns. In oil and gas operations, water is needed to drill and complete wells. It also needs to be treated for bacteria prior to drilling or hydraulic fracturing, as any trace of bacteria in water can cause reservoir souring and corrosion issues.
Eliminating the presence of bacteria is something that oil and gas operators have dealt with by utilizing treatments involving a variety of chemical-based biocides. The challenge is that traditional disinfection treatments require harmful chemicals to be physically transported to and from the site. This exposes not only the personnel working with the chemicals but also the communities through which the chemicals are transported. While this has been adopted as a standard practice, the industry challenges itself to find safer, greener solutions that can address the issue at hand: safe removal of bacteria in a cost-effective manner.
Current water treatment technologies in the oil and gas industry offer opportunities to reuse flowback water from hydraulic fracturing applications. This minimizes fresh water requirements and reduces demand on regional water systems. In addition, oil and gas extraction creates substantial quantities of “produced” waters with varying levels of contamination, which must be disposed of through treatment or reinjection. Produced water is extracted at an average rate of 2.4 billion gallons per day (gpd), and over 80 percent of production occurs in the Western United States.1 It represents the largest waste stream associated with oil and gas production, with estimates of almost 2.7 million acre-feet per year.2 Operators must learn how to reuse produced water in operations, turning what was once a waste into a resource.
The mass production of water brings tremendous disinfection and recycling opportunities with it. The bacteria present in the produced water needs to be eliminated before it can be reused as a frack fluid. If left untreated, the bacteria present in the frack fluid will sour an otherwise sweet system, producing organic acids that can exist in “microenvironments” under deposits present in systems. If bacteria are present in a wellbore, it will increase operational expenses as a result of the corrosion (H2S pitting, stress cracking, etc.) in both the surface and subsurface tubulars, and related prevention expenses.
One traditional method for disinfecting produced water adopted as a standard practice in the oil and gas industry is the use of chlorine dioxide as a primary disinfecting agent. This method does give results; however, there are some important considerations that need to be addressed when evaluating the advantages and disadvantages of available water treatment processes. These include safety, environmental impact, energy requirements, disposal options and unanticipated costs.
As the industry becomes more efficient, traditional bacteria treatments are being displaced by solutions that address safety concerns while delivering effective disinfection results. What operators are coming to understand is that the components and current use of traditional technologies can, in fact, be less effective and potentially more harmful to personnel and the environment — and more expensive should a safety incident occur.
Challenges with Chlorine Dioxide
As noted above, chlorine dioxide is commonly used as a disinfection treatment but it does come with risk, including risk to personnel, environmental impact, and costs that may be associated with any potential incident that arises. According to the National Institute for Occupational Safety and Health (NIOSH) standards Publication Number 2005-110, the Short-Term Exposure Limits (STEL) for Chloride Dioxide is 0.3 ppm. This means that all personnel associated with or handling chlorine dioxide are required to wear a ClO2 air quality detector. If the air quality reaches the threshold limits, all personnel must be sent for chest X-rays on a yearly basis.
Chlorine dioxide has an Immediate Dangerous to Life or Health (IDLH) of 5 ppm. For reference, the IDLH of H2S is 100 ppm. As a result of the IDLH, the recommended best practice for chlorine dioxide treatments requires two personnel on location at all times. This means additional personnel have potential exposure to harm.
Chlorine dioxide is typically generated on site. The costs associated with generation depend upon the price of the chemicals that are used to produce chlorine dioxide. In general, chlorine dioxide is approximately 5 to 10 times more expensive than chlorine,3 which is also widely used as a disinfecting agent. Apart from the costs of generation on site, there are additional costs associated with chlorine dioxide, such as required safety training as well as additional safety audits that service contractors and operators must incur. In addition, the requirement of having two operators on location translates into additional costs for both the service company and the operator.
New Technologies Introduce Opportunities for Water Reuse and Treatment
As the volume of water utilized in fracturing operations has increased significantly with extended horizontal laterals, operators are reusing water in their operations more than ever before. Today, technically-differentiated service offerings are available to provide high throughput volumes to disinfect bacteria and treat water for storage and pit maintenance, on-the-fly disinfection prior to hydraulic fracturing operations, and salt water disposal (SWD) injection without the use of harmful chemicals.
One example is the Free Radical Disinfection (FRD) solution from Gradiant Energy Services (GES). It has three main components: table salt, water and an electrolytic cell to generate sodium hypochlorite and hydrogen peroxide on site. The ions bind to and remove the bacteria, resulting in bacteria-free water that maintains the integrity of the reservoirs for extended periods of time.
This technology provides an effective kill in both fresh water and produced water applications, while limiting exposure to personnel on location. The costs associated with this approach are limited as it requires only one person to run the system and table-grade salt is the only chemical utilized, providing a greener solution for operators. The cost-effective technology can be used for on-the-fly frack treatments and/or treatment at a pit or saltwater disposal well.
Oil and gas operators are looking for innovative solutions that lower their operating costs without sacrificing safety and service quality. The advent of new technology is pushing boundaries in how to treat water in a greener and safer way. As a result, service companies are leveraging new technologies to tackle this very issue and encouraging operators to look at water treatment in a whole new way.
About the Authors:Devatava Vashishtha is a technical support engineer with Gradiant Energy Services, assisting the sales team with new projects. He has a bachelor of science in chemical engineering from the National Institute of Technology Raipur, India, and a master’s in petroleum engineering from the University of Houston, making him adept in both upstream and downstream oil and gas operations. Julie Villalobos has worked in the oil and gas industry since 2001, with both service and operating companies. She is currently the vice president of sales and marketing at Gradiant Energy Services. Villalobos holds a bachelor of science in civil and environmental engineering from the Ohio State University. Danny Jimenez joined Gradiant Energy Services in January 2017 and serves the company as chief executive officer. With more than 23 years of experience in the oilfield services and executive experience in growing service companies, he is a strong advocate for the responsible development of domestic oil and gas resources.
References
1. Clark, C. E., and J. A. Veil. Produced water volumes and management practices in the United States, Report No. ANL/EVS/R-09-1, Argonne National Laboratory (ANL), 2009.
2. Dahm, K., and M. Chapman. Produced Water Treatment Primer: Case Studies of Treatment Applications, US Department of the Interior, Bureau of Reclamation, Technical Service Center, 2014.
3. “Disinfectants Chlorine Dioxide,” Lenntech website, accessed October 2017. http://www.lenntech.com/processes/disinfection/chemical/disinfectants-chlorine-dioxide.htm
