Investigation of Microorganisms in a West Texas Oilfield Using Growth and Genetic Testing

Abstract

Abstract Increasing corrosion issues at a sour west Texas oilfield in the Permian Basin suggested that microbiologically influenced corrosion (MIC) could be the cause. However, multiple water and biofilm samples failed to show significant concentrations of microorganisms using traditional microbial growth media for the cultivation of APB, GHB and SRB. Microbial growth tests indicated the highest concentration of microorganisms as 103 cells/ml, while the results of genetic testing using qPCR indicated that microbial concentrations of up to 1000-fold higher were actually present. It was speculated that the type of microorganisms present in the samples from this saline (6 to 10%) thermophilic (60°C) field may not grow well in the standard microbial growth media. Additionally, isotopic analysis of sulfur in the hydrogen sulfide gas and in sulfate from formation water are consistent with microbiological sulfate reduction being responsible for reservoir souring at this location. To characterize the microbial community composition of these samples more thorough DNA sequencing was performed on selected samples. The results of DNA sequence analyses show that the percentage of unclassified DNA sequences (unidentifiable at the genus level because no similar DNA sequences are present in the global database) ranged from 1.8% to 25.8%. Of the bacteria that could be identified, a high percentage of halophilic (salt loving) bacteria, and of SRB were observed in all samples. These results demonstrate that genetic testing can provide data about microorganisms in some oilfield samples, even when standard microbial growth tests fail to indicate the presence of microorganisms. Moreover, standard microbial growth recipes are not well suited for the growth of microbes from all locations and there is a need for new formulations of microbial growth media for use in some locations, such as the Permian Basin. Using standard microbial growth tests in this case would have seriously under-estimated the integrity risk caused by the presence of high numbers of SRB that were demonstrated to be present by genetic analyses. Armed with the knowledge that significant concentrations of microbes were indeed present, but had different nutritional requirements than those provided in standard microbial growth media, new formulations of microbial growth media were developed by Intertek that are tailored to the requirements of these Permian Basin samples.