Hydrogen sulfide gas produced by sulfate reducing microorganisms (SRM) creates significant challenges in the petroleum industry including corrosion concerns, product devaluation, and significant health risks. Biocides and inhibitors are often employed to control these detrimental activities. Recently, co-injection of a synergistic blend of biocides and the SRM inhibitor, nitrite, was proposed as an effective means to control biogenic sulfide production, however, the method only addressed inhibition of SRM activity and not kill. Inhibition can have the undesirable consequence of allowing SRM to resume full activity once the inhibitor is depleted, thus requiring the continuous input of expensive chemicals to maintain control. On the other hand, biocides are designed to reduce SRM concentrations thus reducing the need to add additional chemical until the SRM population re-establishes. Lab results, using an SRM field enrichment, demonstrated that the sequential injection of nitrite inhibitor followed by glutaraldehyde led to an 8-log reduction in SRM while only a 2-log reduction when co-injecting these chemicals at equivalent concentrations. It is proposed that pretreatment with the inhibitor, nitrite, or other respiratory inhibitor, results in a reduction in cellular ATP of the SRM creating a sublethal stress response allowing for their enhanced kill upon subsequent biocide addition.
The lengthy laterals of horizontal wells often pose microbiological challenges, as they provide more area to become microbially contaminated and require larger volumes of fluid and biocide for treatment. A Permian Basin oilfield has been experiencing MIC-related failures in its horizontal wells, which is of concern due to the associated high workover cost.
Laboratory biocide challenge testing identified several common oilfield chemistries and combinations thereof as being effective against this field’s population of microbes. However, aggressive applications of these products in the field neither delivered an effective microbial kill nor prevented the treated wells from experiencing further MIC and failures.
An acrolein field trial was conducted on a set of problematic, microbially contaminated horizontal wells over a time period of approximately one year. During this timeframe, these wells experienced microbial control for the first time, defined as meeting and maintaining microbial KPIs. Additional benefits were realized as a result of acrolein, including a dramatic improvement in water quality evident as a decrease in iron sulfide and suspended solids, a clean-out of the wells inferred by an initial increase of solids post-acrolein, a decrease in the corrosion rate as indicated by a significant reduction in iron and manganese counts, a decrease in the well failure rate, an increase in production, and an overall cost savings associated with the application of acrolein.