Real-Time Field Monitoring To Optimize Microbe Control
- Vic Keasler (Nalco)
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- April 2012
- Document Type
- Journal Paper
- 30 - 33
- 2012. Copyright is retained by the author. This document is distributed by SPE with the permission of the author. Contact the author for permission to use material from this document.
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Microbial growth in oil and gas systems can cause numerous problems that result in production downtime, lost revenue, and safety concerns. Unfortunately, microbial populations are ubiquitous in many oil and gas production zones and minimizing their impact is challenging. The most common effects of microbial growth are corrosion, hydrogen sulfide (H2S) production, and biofouling.
The ability to minimize the negative impact of microbes is confounded by the current field monitoring technology, which is unable to detect many of the organisms. These monitoring technologies are culture-based, meaning that organisms must be grown in culture to be detected and quantified. It is well documented in many systems that less than 1% of the total organisms present are culturable. In addition, the culture-based methods commonly take days or weeks to produce a result. Thus, operators must wait a considerable time before taking control measures, and the impact of microbial populations can increase during the long period of undetection.
New Development in Monitoring Method
Two essential parameters for any new field monitoring technology are the ability to obtain a result in real time and the ability to detect all organisms, not just the ones that can be grown in culture. The industry has evaluated several of these technologies over the years, including a first-generation adenosine triphosphate (ATP) assay in which the level of ATP is used to measure the number of actively growing microbes in a sample.
ATP is the molecule used by cells to drive any process that requires energy. This includes metabolism, protein translation, DNA repair, and cell division. Although there are differences in the absolute quantity of ATP in different species or organisms, it is assumed that actively growing bacterial cells hold relatively similar amounts of ATP, and a calculation has been determined to quantify microbial cell numbers based on a measurement of ATP.
The major challenge of using this technology in oilfield systems is that the enzymatic assay used to quantify ATP is very sensitive to the quality of the fluids tested. This means that many oilfield fluids such as oil, emulsions, produced water with significant solids, high-salinity fluids, and fluids contaminated with certain chemicals would not yield meaningful results. As an example, the first-generation ATP test was not generally accepted by oilfield operators and has been little used. However, a second-generation ATP test that addresses the concerns has been developed recently. Specifically, additional steps were developed to enable accurate testing of fluids that contain oil, high salinity, residual chemicals, and solids. This technology also meets the other necessary criteria—real-time results and detection of all microbes, not only those that grow in culture.
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