|“Control of Microbial Contaminants in Hydraulic Fracturing Processes”|
By Dr. Terry M. Williams
The Dow Chemical Company
The recovery of oil and natural gas from previously untapped petroleum reserves plays an important role in the global energy market. A critical component of oil and gas production is the utilization of water in the process. Hydraulic fracturing uses extremely large volumes of water and effective management of this resource is critical to the quality and efficiency of the production process. Effective microbial control in unconventional shale gas systems is required to reduce the risk of formation damage from the growth and metabolism of microorganisms in the down hole (reservoir) environment. The primary microorganisms of concern are sulfate-reducing and acid-producing bacteria. Key problems caused by these anaerobic microbes include souring (sulfide), corrosion (organic acids), and plugging (biofilms, iron precipitates).
Industrial biocides are added to hydraulic fracturing injection water to control the growth and development of problematic microorganisms. These biocides are registered and regulated by EPA and PMRA within North America. Biocides are selected based on their spectrum of activity, speed of kill, compatibility with additives, and stability under process conditions. In many cases, combinations of biocides are used to provide both short term control and long-term preservation. Efficacy testing involves specialized growth conditions and selective culture media for the various groups of anaerobic bacteria. Modern molecular-based methods are also useful for more rapid analysis of microbial problems and evaluation of population diversity. This presentation will provide a summary of the problems caused by microorganisms in hydraulic fracturing, the key organisms of concern, methods for monitoring contamination, biocides used for microbial control, and regulatory/sustainability issues.