"Kills 99.9% of bacteria". Sounds impressive. Consumers will have seen this claim on supermarket shelves on all kinds of household biocide chemicals such as hand soaps and detergents. In reality, what does this actually mean? Is a kill target of 99.9% an effective biocide? On the face of it, it sounds very good. However, when referring to microbiological populations, like bacteria, this requires context. What was the original number that was reduced by 99.9%? When quantifying microbiological populations, it is common to use extremely large numbers, referenced in logarithms (1.0 × 105 or 1.0 × 106 cells). Reducing bacterial populations by 100% using batch dosed biocide chemicals is an impossible feat. It will never be possible to entirely eliminate 100% of bacterial populations, as some will always survive and potentially recover to pre-dose populations. Therefore, selection of the most efficient biocide chemical is of the utmost importance. In the example scenario of a hand soap, the target of 99.9% is very difficult to achieve. The biocide chemical is applied to the target surface area (hand) and almost immediately diluted and washed off by a running stream of water. The chemical might get a contact time of up to 1 minute to kill 99.9% of bacteria under normal circumstances. Although hand soap is not directly related to control of bacterial populations in oilfield process systems, the theories behind the testing of all biocide chemicals are the same. It boils down to three parameters that need to be tested; chemical, concentration and contact time, tested against microbiological populations. The questions any operator should ask before using a biocide chemical should be; Which biocide chemical?What concentration should be applied?How long should the biocide chemical be added for? By answering these questions, the operator will have learned key points as to the efficiency of the biocide chemicals under test in relation to the required conditions. This paper will discuss a recent example of a biocide chemical evaluation carried out by a Malaysian operator, in which fourteen different biocide chemicals were tested to determine the most efficient biocide chemical. Each biocide chemical was tested under controlled laboratory conditions against both planktonic and sessile mixed microbial consortia populations, and ranked for efficacy.
Biocide chemicals are an essential control in the oil and gas industry. From drinking water to hydrocarbon production streams, it is necessary to use the correct chemical, at the correct dose to prevent uncontrolled microbiological activity. The objective of this review is to discuss an example of a biocide evaluation that tested seven (7) different biocide chemicals (from the same chemical vendor) against planktonic and sessile microbial populations by both traditional and molecular microbiological monitoring techniques. The methods used in the biocide evaluation were in accordance to internationally recognised standards; NACE TM0194-2014 ‘Field Monitoring of Bacterial Growth in Oil and Gas Systems’ and NACE TM0212-2012 ‘Detection, Testing, and Evaluation of Microbiologically Influenced Corrosion on Internal Surfaces of Pipelines’. The procedure stated that 7 biocides at 2 concentrations (500ppm and 1000ppm of product) were to be tested against bacterial populations (planktonic and sessile), in relation to appropriate water chemistry and microbial consortia. The microbiological techniques used to determine the biocide efficacy were; traditional Most Probable Number (MPN) bacterial enumeration of; Sulphate Reducing Bacteria (SRB), General Heterotrophic Bacteria (GHB) and Acid-Producing General Heterotrophic Bacteria (APGHB), Quantitative Polymerase Chain Reaction (qPCR) with pre-selected primers for SRB, Sulphate Reducing Archaea (SRA), and lastly, Next Generation Sequencing (NGS). The results from the microbiological techniques allowed for an evaluation by ranking each biocide chemical in comparison to the total test group of chemicals, against untreated controls. Performance was based on the reduction of microbiological populations from the untreated control populations and greater microbiological community detail was achieved through interpretation of the molecular techniques data. The inclusion of molecular microbiological monitoring techniques to biocide evaluations is a novel approach to understanding the direct impact of biocide chemicals in greater detail. In turn, this approach will provide knowledge and valuable information for chemical addition optimisation and cost saving.
Microbiologically Influenced Corrosion (MIC) is a well-documented phenomenon that involves microorganisms and affects multiple industries with untold economic impact. The most well-known microorganisms within the oilfield, by far, are Sulphate-Reducing Bacteria (SRB). It is thought that through SRB respiration, corrosion of metals can occur. An exact figure for MIC responsibility in overall corrosion is currently unknown. However estimates of between 10-50% are not uncommon, when coupled with estimated costs of metal corrosion in developed countries to be between 2-3% of Gross Domestic Product (GDP), suddenly the cost implications of MIC gain significance. The technical and economic implications have gained recognition within the oil and gas industry within the last thirty to forty years and monitoring techniques to detect microorganisms and corrosion have progressed and developed through increased interest in microorganisms commonly found within the oilfield. As with human nature, the ability to predict the future, rather than deal with the consequence is a preferred approach, which is one of the main driver's to pro-active monitoring techniques for detection of microorganisms to help determine the risk of MIC to occur, rather than a reliance on rate of corrosion alone. This approach has led to increased research in to the subject of oilfield microbiology and development of modern molecular techniques, often borrowed from other industries such as medical microbiology, that have come to the fore recently. However a significant focus on cost saving practices within the oil and gas industry has a significant and direct impact on the type and frequency of monitoring applied (if any).The objective of this review is to discuss and evaluate the available techniques and review the most common problems associated with microorganisms within the oil and gas industry. To determine effective monitoring practices in a practicable and economically viable manner to ensure monitoring can be carried out effectively, understood and evaluated while implementing control and mitigation strategies with confidence.
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