Biodegradação de inibidores de incrustação por culturas puras e mistas de bactérias redutoras de sulfato

Abstract

Enhanced Oil Recovery (EOR) is used in the oil extraction, aiming to extract maximum amounts of the oil reserves. These high complexity procedures are based on the stimulation of wells through the injection of chemical additives, which may contain substances, such as carbon, nitrogen and phosphorus, crucial for the undesirable growth of sulfate-reducing bacteria (SRB), which can use the combination of these injection fluids with the saline water and the oil as a growth medium suitable for their development, leading to fouling, corrosion and production of H2S in the oil recovery system. Consequently, this generates an increase in the expenses required with biocides, moreover, causing a drop in productivity. For the experiments, four different bacterial cultures were tested (CP, 879, CT3 and CT9), 2 pure and 2 mixed, containing SRB in the presence of different additives. Five additives were used for this, numbered from 8 to 12, and the growth of these cultures was evaluated through qualitative and quantitative tests of growth in culture medium. Furthermore, kinetic experiments were carried out to evaluate the production of H2S by each culture in the presence of each additive through kinetic curves of biogenic sulfide production. From the qualitative analyses, it was possible to observe that, while in the media without the presence of additives all four cultures showed growth, in the media in the presence of these additives, there was bacterial growth only in the mixed cultures containing additives 8 and 12 and in the pure culture CP containing additive 8. Both these additives are based on organic phosphonates, so it was possible to observe that they can be degraded by SRB cultures. The other three additives (9, 10 and 11), which were not degraded, have their composition based on maleic acid copolymers, indicating that these compounds were not decomposed by the SRB. As for the quantitative tests, comparing the growth of these cultures in the presence and without the presence of additives, the results showed that the cultures that grew in medium without additive showed growth up to much higher dilutions than those in medium containing additives. Although this indicates an inhibitory effect on microbial growth, expected for these additives, they were not able to completely inhibit the SRB growth. With the kinetic experiments, it was possible to trace the kinetic curves of accumulated production of H2S for each bacterial culture. The cultures showed very different biogenic sulfide production rates. The CT3 mixed culture showed a slight reduction in H2S production in the presence of the additives, while the CT9 culture showed an increase in production, greater for additive 8 than compared to the additive 12, whereas the CP culture did not present a substantial change in production. Finally, 879 culture did not grow in the presence of additives. Subsequently, analogous were made to carried out, but in the presence of reservoir rocks containing microorganisms, which allowed the comparison between the results. However, microbial growth did not occur properly due to the bacteria found in these rocks through metagenomic analysis.