Microbial growth in oilfield waters contributes to biofouling and microbiologically influenced corrosion (MIC), necessitating effective monitoring techniques. This study provides a comparative assessment of three microbial detection methods—quantitative polymerase chain reaction (qPCR), adenosine triphosphate (ATP) assay, and Bactiquant—each employed to monitor microbial growth and activity in oilfield water systems. We explore their respective capabilities, limitations, and suitability for field and lab environments. Results suggest that while ATP and Bactiquant offer rapid field-deployable options for general microbial quantification, qPCR delivers high specificity, critical for targeting corrosion-related microbial populations like sulfate-reducing bacteria (SRB).
1. Introduction
Microbial growth within oilfield water systems poses significant operational challenges, as microorganisms contribute to biofouling and accelerate microbiologically influenced corrosion (MIC) through the production of metabolites such as hydrogen sulfide. Effective microbial monitoring methods are essential for maintaining system integrity and minimizing corrosion risks. Techniques such as quantitative polymerase chain reaction (qPCR), ATP assay, and Bactiquant represent leading options for detecting microbial activity in oilfield environments. This article compares these methods based on specificity, speed, and field suitability, with a focus on their ability to detect corrosion-related microbes, especially sulfate-reducing bacteria (SRB).
2. Comparison of Microbial Detection Techniques
2.1 Quantitative Polymerase Chain Reaction (qPCR)
Quantitative polymerase chain reaction (qPCR) is a molecular-based technique used to detect and quantify specific microbial DNA sequences, enabling identification of targeted microbial communities such as SRB. qPCR amplifies specific gene sequences associated with sulfur reduction and other corrosion-related microbial processes, making it a powerful tool for understanding microbial dynamics in oilfield waters.
The high specificity of qPCR allows for the precise detection of individual microbial groups that are known contributors to MIC. This capability is advantageous in corrosion monitoring, where identifying SRB and other specific microbes can help operators tailor microbial control strategies more effectively. However, qPCR requires specialized equipment and trained personnel, making it predominantly a laboratory-based technique. Its use in the field is limited by these logistical demands, as well as by the associated costs, which may restrict its accessibility for real-time microbial monitoring in oilfield settings
2.2 ATP Assay
The ATP assay is a widely utilized technique in the oilfield sector, offering a quick and straightforward method to estimate microbial biomass by measuring ATP, the universal energy molecule present in all living cells. The ATP assay detects cellular ATP levels using a luciferase-based reaction that produces light, which correlates with the microbial biomass present. This approach provides a rapid means of assessing general microbial activity, aiding in routine monitoring and evaluating biocide efficacy.
Despite its speed and ease of use, the ATP assay has limitations. It lacks the ability to distinguish between different microbial species, such as SRB, thus providing only a general estimate of microbial activity rather than targeting corrosion-related microbes specifically. Moreover, ATP is known to degrade quickly, which can affect accuracy in certain conditions, such as during biocide testing where residual ATP may continue to fluoresce briefly after cell death. Despite these limitations, the ATP assay remains popular in oilfield settings for its practicality and rapid response
2.3 Bactiquant
Bactiquant technology is a fluorometric method that provides a general measure of bacterial activity by detecting hydrolase enzyme reactions in bacterial cells collected on a membrane filter. The method involves filtering microbial particles, which are then exposed to a fluorescent substrate, yielding a Bactiquant value that reflects total microbial activity in the sample.
Bactiquant is notable for its portability, low training requirements, and rapid results, making it a convenient choice for field deployment. The method has been validated by the EPA for monitoring potable water, attesting to its reliability. However, like the ATP assay, Bactiquant provides an aggregate measure of bacterial activity without differentiation among microbial species. This nonspecificity is a limitation in MIC contexts, where distinguishing corrosion-causing organisms like SRB from other microbial populations is critical. Additionally, Bactiquant results do not directly correlate with colony-forming units (CFUs), complicating comparisons with traditional microbiological methods. Mycometer, the developer of Bactiquant, is working toward an appropriate conversion for standardized reporting
Summary of Techniques
The unique attributes of qPCR, ATP assay, and Bactiquant make each method suitable for different monitoring needs in oilfield water systems. Table 1 provides an overview of the key advantages and limitations of each technique.
| Technique | Primary Function | Specificity | Field Suitability | Limitations |
|---|---|---|---|---|
| qPCR | Detects and quantifies specific DNA or RNA sequences | High, detects SRB and other target microbes | Used to be laboratory-based. MICBUSTERS offers field kit | Requires qPCR equipment and training. Is not suitable to distinct between living and death cells |
| ATP Assay | Measures microbial biomass by ATP detection | Low, general microbial estimate | High, rapid field response | Lacks species specificity, ATP degrades rapidly |
| Bactiquant | Measures bacterial activity via enzyme fluorescence | Low, general bacterial measure | High, portable and EPA-validated | Does not differentiate microbial species; results not CFU-equivalent |
4. Conclusion
For general microbial activity monitoring in oilfield waters, ATP assay and Bactiquant provide quick, field-compatible options, allowing operators to make real-time adjustments to biocide dosing and microbial control efforts. However, for applications where identification of specific corrosion-related organisms, such as SRB, is essential, qPCR remains the superior method. Although qPCR’s specialized requirements limit its field use, its species-level detection and quantification capabilities make it an invaluable tool for lab-based microbial analysis in corrosion studies. Future advancements in portable qPCR technology could enhance field applicability, offering comprehensive microbial monitoring directly at oilfield sites.
References
- Robertson, A. (2016). Real-Time, Low-Cost Technologies for Determining Treated Oil and Gas Produced Water Stability (Master’s Thesis). Texas A&M University.
- LuminUltra. (n.d.). ATP Technology.
