The paper reports microbiological study of Sulfate Reducing Bacteria activity in underground gas storage and preventive action against H_2S formation. Complex research was performed on natural gas reservoir in Swarzow, where one of a few gas storages in Poland had been arranged. The presence of hydrogen sulfide in the 10-th cycle of UGS exploitation gave impact to search a new effective methods which might limit the microbial processes of sulfate reduction in the reservoir. Having the long-term experience, in 1995-96 operation of biocide treatment in SWARZOW UGS was completed with success. Selective biocides (quaternary ammonium compounds) were applied into the reservoir for the first time in Poland, in accordance with patented technology worked out in Oil and Gas Institute, Department of Microbiology. In 1997-98 the biocide injections to exploitation wells were repeated. These operations conduced to the total elimination of Sulfate Reducing Bacteria from the formation waters and caused partial reduction of H_2S content in natural gas recovered from the reservoir. In 2003 the new technology based on synergetic action of biocide, represented by triazine derivatives, and H_2S Scavenger (Sulfa Clear) was implemented for the first time in underground environment. Practical application of this technology on 2 objects of UGS was finished with a great success. Content of hydrogen sulfide in the recovered gas and formation waters now accords with European Standards. The paper also discusses microbiological studies of processes observed in the natural gas reservoir in Wierzchowice, which is the largest store in Poland. Its final capacity will be ca. 4,3 billion cubic meters of natural gas. The research was conducted between the 1st and the 8th cycle of UGS exploitation. Present investigations were performed in the monitoring system and included microbiological and chemical analysis of formation waters and drilling fluids. Active strains of H_2S producing bacteria (Desulfovibrio sp. And Desulfotomaculum sp.) isolated from the reservoir, have been used for testing biocides selected to protect exploitation wells of WIERZCHOWICE UGS.
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