Traditional biocide treatment for control of sulfate reducing prokaryotes (SRPs) and acid producing bacteria (APB) in oil and gas operations typically targets topside operations and often neglects the reservoir. Often, the efficacy of these biocide program is limited and do not extend for longer periods into the reservoir. This study evaluates the performance of glutaraldehyde, the most widely used effective biocide, for reservoir protection along with a synergistic combination of oxazolidine biocides. This combination provides medium to long term protection of the system and thereby controls both mesophilic and thermophilic bacteria in the reservoir.
Produced water samples from a conventional reservoir from the Middle East and Africa and unconventional reservoir from the United States were collected and a novel microbial control program was tested under heat-aged conditions with a combination of glutaraldehyde and oxazolidine type biocides. This combination provided protection (3 log10 reduction of viable counts) against repeated APB/SRP inoculation over a 30 to 64 days' time frame at varied biocide concentrations. Th results from the heat-aging of the produced water and biocide at 75°C showed that the effectiveness of this combination can be successfully applied to achieve long term protection against biological souring in the reservoir.
Biocides play a critical role in the oil and gas industry as they are used as chemical additives during drilling, completions, and water-flooding operations. Their primary purpose is to prevent various problems such as the formation of biogenic H2S, microbiologically influenced corrosion (MIC), and reservoir plugging caused by microbial growth. With advancements in horizontal drilling and well completion technologies, the economic exploration of unconventional energy resources has become possible alongside traditional drilling methods. However, it is important to address microbial control associated with these activities, especially due to the substantial amounts of injection water utilized in secondary recovery in conventional methods and during hydraulic fracturing operations in unconventional methods. One significant concern, due to the uncontrolled microbial activity, is the souring of reservoirs. Souring can occur naturally or as a result of the actions of sulphate reducing prokaryotes (SRPs) [1]. Controlling microbial growth with biocide treatment programs becomes essential to prevent the introduction of unwanted microorganisms into the reservoir and to inhibit or eliminate endemic microorganisms present within the fractured formation. While conventional biocide treatments have primarily focused on disinfecting injection water to protect the well's surface, less attention has been given to ensuring the overall integrity of the reservoir itself. This oversight could potentially lead to unforeseen complications in the reservoir over the long term [2,3]. Therefore, it is crucial to prioritize microbial control strategies that take into account the long-term reservoir integrity and consider the potential consequences of neglecting reservoir-wide protection. An important consideration is the development of a biocide program that can rapidly disinfect injection water while maintaining persistence in down-hole environmental conditions. This means that the biocide should continue to be effective over an extended period, even in the challenging and dynamic subsurface environment. By achieving these objectives, the industry can mitigate potential environmental risks while ensuring the integrity and productivity of the wells and reservoirs.
