Hydrogen sulfide generation in oil production is a constant cause of concern. In several cases this phenomenon occurs due to the action of sulfate-reducing bacteria. Various methods, including biocides and nitrate addition, have been used to control the activity of these microorganisms, but they are expensive and have side effects. Other inhibition methods, such as the use of molybdate, have received much less attention. This study performed a kinetic test for the inhibition of sulfate reduction, and shortterm tests to determine the minimum inhibitory concentration of molybdate in liquid medium containing 10.4 and 20.8 mM of sulfate (1000 mg L -1 and 2000 mg L -1 ), respectively. An inoculum was prepared from a microbial consortium of sulfate-reducing bacteria dominated by Desulfovibrio vulgaris enriched from produced water from oil wells of the Reconcavo Basin, Brazil. The indicators of bacterial activity used were: sulfate reduction, sulfide production, culture medium color, pH, and redox potential. The tests show that, regardless of the concentration of molybdate, sulfate reduction is inhibited after the first hours of the start of the test. The conversion of sulfate in the kinetic experiment without molybdate is 78%, whereas the average conversion in the experiment with molybdate is approximately 30% in 216 h. The short-term test results show that 0.08 mM (12.8 mg L -1 ) molybdate, a molar ratio molybdate/sulfate of 0.004, is sufficient to inhibit the activity of sulfate-reducing bacteria for 168 h.

The activity of anaerobic sulfate reduction was studied using sulfate-reducing bacteria isolated from the water produced from a Brazilian oil reservoir. The effects of the initial sulfate concentration on the anaerobic sulfate reduction and sulfide generation kinetics were investigated. The redox potential, the biomass solution content, and the sulfate and the sulfide solution content were measured. The results indicate that the sulfate conversion and the sulfide generation are both first-order processes for the initial sulfate concentration of 823, 1,282, and 1,790 mg/L. The results for the kinetic constants for the sulfate conversion indicate an inhibition with the enhancement of the initial sulfate solution content. The kinetic constants for the sulfide generation indicate that this reaction is almost independent of the initial sulfate solution content due to the presence of at least two in-series processes that are faster than the microbial conversion of the sulfate. The kinetic test using the water from an onshore oil field, with an initial sulfide content of 228 mg/L and sulfate content of 947 mg/L, shows a sulfate conversion of 50 % in 528 h. The kinetic modeling for the net content of sulfate and sulfide indicates that the sulfate conversion is slower for this water than for the deionized water tests; however, the sulfide formation has almost the same conversion velocity. The reactions are first order in both cases.

Souring of oil fields during secondary oil recovery by water injection occurs mainly due to the action of sulfate-reducing bacteria (SRB) adhered to the rock surface in the vicinity of injection wells. Upflow packed-bed bioreactors have been used in petroleum microbiology because of its similarity to the oil field near the injection wells or production. However, these reactors do not realistically describe the regions near the injection wells, which are characterized by the presence of a saturated zone and a void region close to the well. In this study, the hydrodynamics of the two-compartment packing-free/packed-bed pilot bioreactor that mimics an oil reservoir was studied. The packed-free compartment was modeled using a continuous stirred tank model with mass exchange between active and stagnant zones, whereas the packed-bed compartment was modeled using a piston-dispersion-exchange model. The proposed model adequately represents the hydrodynamic of the packed-free/packed-bed bioreactor while the simulations provide important information about the characteristics of the residence time distribution (RTD) curves for different sets of model parameters. Simulations were performed to represent the control of the sulfate-reducing bacteria activity in the bioreactor with the use of molybdate in different scenarios. The simulations show that increased amounts of molybdate cause an effective inhibition of the souring sulfate-reducing bacteria activity.

O monitoramento de escavação é uma forma concisa de avaliar o desempenho operacional do desenvolvimento de uma galeria através do acompanhamento dos índices de overbreak, underbreak e a qualidade da escavação. Ao iniciar o desenvolvimento das galerias subterrâneas os fatores não controláveis intrínsecos ao maciço rochoso devem ser avaliados de modo que as falhas operacionais peculiares ao processo sejam minimizadas, principalmente, na execução das atividades de marcação topográfica das frentes e perfuração horizontal. Para garantir melhor controle, tornar mais confiáveis às medições dos índices, realizou-se uma retroánalise dos levantamentos das escavações da Mineração Caraíba S/A, determinando os índices de overbreak e underbreak, a qualidade das escavações e correlações entre a razão de carregamento e os indícios foram investigados.

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