New Biocide Formulations for Oil and Gas Injection Waters with Improved Environmental Footprint
Authors: Enzien Michael V. , Yin Bei 
Published: May 2011

Abstract
Combinations of various biocides with Glutaraldehyde or THPS (tetrakis hydroxymethyl phosphonium sulfate), the two most commonly used injection fluid biocides in the oil and gas industry, showed both improved performance and lower environmental aquatic toxicity profiles. Treatment conditions included temperatures up to 80°C, salinities as high as 15%, and contact times for as long as 7 days. Combination tests were evaluated against both Sulfate Reducing Bacteria (SRBs) and Acid Producing Bacteria (APBs). Many of the new formulations tested had a lower environmental aquatic toxicity profile than either glutaraldehyde or THPS alone because of the favorable aquatic toxicity profiles of the complimentary combination actives. Therefore, these new formulations not only improved or equaled performance of incumbent biocides but did so with a better environmental footprint. The new biocide formulations were developed for treatment of injection waters used in water flooding or hydraulic fracturing applications. In both applications, improved heat stability and thus longer preservation were goals for new product development.

1. Introduction
Microbial control in the oil and gas industry is primarily practiced to prevent the detrimental effects of microbial growth on production equipment, pipelines, and the reservoir. These effects are well known in the industry and include: biofouling (Videla et al., 1995), microbiologically influenced corrosion (Pope, 1991; Videla, 1991), microbial souring (McInerney and Sublette, 1997; McInerney et al., 1993), i.e. biogenic production of H2S; and reservoir permeability reduction (Khazipov et al., 1993). The impact of the detrimental effects of poor microbial control results in lost production time, poor quality crude oil and gas, and occasionally dramatic pipeline failures.
While it is well known that thermophilic bacteria exist and predominate under reservoir conditions (Leu et al., 1998; Mueller and Nielsen, 1996; Nilsen et al., 1996; Pedersen, 2000; Sanchez et al., 1993), most microbial screening tests are still performed on bacteria grown at temperatures well below reservoir temperatures (Johnson et al., 2008; Pope et al., 1990; Ruseska et al., 1982). In addition, most screening tests rarely use contact times longer than 24 hours and if longer contact times are used they do not incorporate re-challenge testing. It is important to provide microbial re-challenges in microbial control screening tests conducted over extended time periods because normal reservoir conditions will contain endemic microorganisms that persist throughout the formation, not just at the near well-bore areas. If re-challenge testing is not used, extended contact times simply represent initial kill which will favor quick acting control products which generally do not provide any extended performance attributes. Tests of this kind really are more of a " disinfection?? study which is not a practical endpoint for oil and gas operations.
Thermal degradation profiles of biocides are well known and many biocides used in the oil and gas industry degrade very quickly under extreme temperatures of deep reservoirs. Many of the biocides that have fast thermal degradation profiles also happen to be the biocides with the fastest mode of action. Likewise, biocides with slow thermal degradation profiles or heat stabile biocides are relatively slow acting. Therefore, in order to meet the performance metrics of both quick-kill and then long-term preservation from extended microbial burdens, the development of combination products was pursued.