Identification of the origin and mechanism of reservoir souring of Esfand, Sivand, and Dena oil fields in the Persian Gulf basin with the use of microbial methods, DNA extraction, and molecular sequencing

The purpose of this research is to identify the source of hydrogen sulfide gas using microbiological, geochemical studies on samples of output, input sea water, and injection water to Sivand (SIC C), Dana (SIC D), and Esfand (SIC E) located in the operational area of Siri Island. Therefore, in order to find out the origin of the reservoir souring of the oil fields of Siri Island, after the initial and library studies, as well as the reservoir characteristics, the history of injection and production of the fields, the most probable hypothesis of the reservoir souring in these fields can be caused by the processes of bacterial sulfate reduction (BSR). Therefore, the culture media required for the growth of sulfate-reducing bacteria was prepared to prove the hypothesis. After field sampling, some microbiology tests were performed on the samples. Since, in initial observations of the sampling, the change in the color of the samples from pink to black indicated that the samples contained sulfate-reducing bacteria. For this purpose, DNA extraction was carried out on the infected samples. In the complementary stage, the samples entered the molecular identification phase. The output of the results was that the bacteria with the highest frequency (about 81%) are Desulfovibrio bacteria, which can consume hydrogen in the oil reservoir and turn them into hydrogen sulfide gas. Therefore, the primary hypothesis of the research is proven. That is the main cause of reservoir souring of the oil fields in Siri Island, the processes related to SRB in which Desulfovibrio bacteria plays a significant role.