Deep drilling often requires the use of circulating fluids to facilitate the drilling process, carrying cuttings and rock fragments to the surface. In this practice, microbial contamination and extensive growth of bacteria in the drilling fluids impact drilling operation and reservoir integrity. An onsite and rapid microbial assessment technique is required to provide an early warning of microbial activities in drilling fluids, and manage microbial risks through proper countermeasures.

Bioluminescence method is a rapid testing technique for quantification of living cells based on the measurement of adenosine-5'-triphosphate (ATP) found in the sample. ATP test has been widely used in food and pharmaceutical industries; however, its application in the oil and gas industry has been hindered by many interference substances present in typical oil industry samples. In this study, we have validated an ATP-based bioluminescence test for its linearity and repeatability in various types of samples from drilling rig operations (make-up water, drilling mud, and cement mix fluid). The results from ATP test showed an excellent linear relationship with the microbial numbers in the samples determined by plate count method. The study proved ATP bioluminescence technique as a reliable method for onsite determination of microbial contamination in drilling operations, obtaining results in minutes, rather than days or weeks with traditional methods.

The action levels based on ATP measurements were recommended for drilling engineers to assess microbial risks in drilling fluids. The implementation of this onsite microbial monitoring technique in the field will facilitate real-time detection and immediate mitigation countermeasures for microbial control in drilling fluids, reducing risks such as loss of rheological properties of drilling fluids from biodegradation, H2S production during drilling downtime and deep in the formation, biomass plugging in the formation, and microbial corrosion. This is the first study of the use of ATP-based test to assess microbial contamination in drilling rig operations.

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