The recovery of petroleum resources from previously untapped shale reserves significantly impacts the global energy market. Effective management of limited water resources and control of microbial contamination in all process fluids are crucial to the sustained quality of production fluids. Microbiological contamination in untreated waters is recognized in the oil and gas industry as posing a high risk of production fluid souring by allowing the growth and metabolism of sulfate reducers. In addition to hydraulic source water contamination, it is expected that microbes can be introduced into shales at the time of drilling, necessitating the treatment of source waters to target existing downhole contamination.
A two-part biocide treatment strategy has been extensively evaluated in controlled laboratory studies. The synergistic combination treatment involves the co-injection of dimethyl oxazolidine (DMO), along with the industry benchmark glutaraldehyde (GLUT). Laboratory testing showed a combination of treatments applied at 1:1 to 1:4 GLUT to DMO active ratios were highly synergistic against bacteria. This ratio provided a rapid kill of sulfate-reducing bacteria (SRB) and acid-producing bacteria (APB), as well as extended control in downhole conditions. Testing conditions were designed to simulate downhole conditions in a North American shale play; subsequently, the shale play was selected for field trials.
A field-wide application of GLUT:DMO in the Niobrara formation was performed from 2012 to 2013. This case study reports 70 hydraulically fractured wells comprised from 25 well pads that received the GLUT/DMO combination treatment. The treatment was successful in maintaining low bacteria counts in the flowback/produced water, using liquid culture media (three positive SRB vials or less). Key advantages of this new treatment strategy include lower total biocide usage versus competitive biocides, an improved environmental (ecotoxicity) profile, enhanced performance at an alkaline pH, and compatibility with process additives.