| Souring of oil formations has become a serious problem for the oil industry in recent years. Especially when seawater is injected into an oil bearing formation, a high production of hydrogen sulfide can be found in many formations after some lag time. Reservoir souring refers to the generation of hydrogen sulfide (H{dollar}sb2{dollar}S) in originally sweet oil reservoirs that have been subjected to (sea)water flooding. Industrial problems associated with hydrogen sulfide production are corrosion, plugging of the petroleum formation, and safety. Also, sulfide production increases the sulfur content of the crude oil which decreases its value and increases refining costs.; The most plausible cause of reservoir souring is the growth and activity of sulfate reducing bacteria (SRB) in the tone where seawater mixes with formation water. In this mixing zone the components supporting SRB growth--electron donors such as organic compounds or hydrogen, electron acceptor such as sulfate, and other essential nutrients such as nitrogen, phosphate, etc.--are present. Abiotic reactions are not considered important in the generation of hydrogen sulfide. They are important, however, in scavenging of H{dollar}sb2{dollar}S since many iron-containing minerals are capable of reacting with H{dollar}sb2{dollar}S forming iron sulfide, pyrite or pyrrhotite.; In this research the current literature on souring in oil reservoirs was reviewed. Two differently operating oil fields were sampled for microbial consortia. An innovative sampling procedure was applied. The obtained consortia were characterized for potential growth substrates for various anaerobic groups of organisms at mesophilic and thermophilic temperatures. Kinetic parameters for microbial sulfate reduction and denitrification were determined at 60{dollar}spcirc{dollar}C. The obtained parameters for sulfate reducing bacteria were determined for suspended as well as for biofilm cells. Batch reactors, completely stirred tank reactors and completely mixed biofilm reactors were wed to estimate the growth kinetics of thermophilic sulfate-reducing bacteria and denitrifying bacteria. The effect of nitrate addition to oilfield waters was demonstrated in laboratory experiments. Microbial sulfate reduction was inhibited when nitrate was added to fresh oil field waters without the addition of bacteria the fundamental mechanisms for this inhibiting effect were investigated. A simulation model based on the experimentally determined growth parameters was developed and described the processes of microbial interaction between SRB and DNB with qualitative agreement to the experimental results. Based on the results of this study, a novel strategy for controlling souring in oil reservoirs undergoing secondary recovery is presented. |
