To study the effect of repeated biocide treatments to mitigate microbiologically influenced corrosion (MIC), we used a Center for Disease Control (CDC) biofilm reactor to generate and remediate corrosive biofilms on carbon steel coupons grown from a produced water sample from a salt water disposal (SWD).
Microbial contamination is a major concern in oil/gas system or industrial water operation where it can result in multiple major corrosion issues and efficiency losses. Chemical treatment is the primary means to control microbial contamination, but due to changes in temperature and water sources, this results in major shifts in the microbial levels and populations which can influence the efficacy of these treatments.
Due to the shifts in the number of bacteria and the change in the dominant microbial species, optimal dosage of biocide is very difficult. Inadequate dosage regimen will result in major losses, whilst excess chemical dosage will incur unnecessary costs whilst also increasing the environmental load. A quick, reliable microbial measurement will help identify critical control points in the process and will allow optimization of dosing of the treatment program.
Agar growth, ATP, and media bottle testing have long been the standard for microbial detection, but these can lack the specificity, sensitivity and response time needed to adequately address the changing conditions in the industrial system described. The molecular-based approach, quantitative polymerase chain reaction (qPCR), described in this article, provides a near real-time method to measure bioburden, allowing operational decisions to mitigate issues to occur more rapidly.
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.