RESUMO
Biodegradation of crude oil in subsurface petroleum reservoirs has adversely affected the majority of the world's oil, making recovery and refining of that oil more costly. The prevalent occurrence of biodegradation in shallow subsurface petroleum reservoirs has been attributed to aerobic bacterial hydrocarbon degradation stimulated by surface recharge of oxygen-bearing meteoric waters. This hypothesis is empirically supported by the likelihood of encountering biodegraded oils at higher levels of degradation in reservoirs near the surface. More recent findings, however, suggest that anaerobic degradation processes dominate subsurface sedimentary environments, despite slow reaction kinetics and uncertainty as to the actual degradation pathways occurring in oil reservoirs. Here we use laboratory experiments in microcosms monitoring the hydrocarbon composition of degraded oils and generated gases, together with the carbon isotopic compositions of gas and oil samples taken at wellheads and a Rayleigh isotope fractionation box model, to elucidate the probable mechanisms of hydrocarbon degradation in reservoirs. We find that crude-oil hydrocarbon degradation under methanogenic conditions in the laboratory mimics the characteristic sequential removal of compound classes seen in reservoir-degraded petroleum. The initial preferential removal of n-alkanes generates close to stoichiometric amounts of methane, principally by hydrogenotrophic methanogenesis. Our data imply a common methanogenic biodegradation mechanism in subsurface degraded oil reservoirs, resulting in consistent patterns of hydrocarbon alteration, and the common association of dry gas with severely degraded oils observed worldwide. Energy recovery from oilfields in the form of methane, based on accelerating natural methanogenic biodegradation, may offer a route to economic production of difficult-to-recover energy from oilfields.
Assuntos
Metano/biossíntese , Petróleo/metabolismo , Alcanos/química , Alcanos/metabolismo , Anaerobiose , Archaea/genética , Archaea/metabolismo , Bactérias/genética , Bactérias/metabolismo , Biodegradação Ambiental , Canadá , Dióxido de Carbono/química , Dióxido de Carbono/metabolismo , Isótopos de Carbono/análise , Gases/análise , Gases/química , Gases/metabolismo , Metano/químicaRESUMO
This study was designed to develop an indirect method for measuring the time required for restoration placement; and to compare the operator time required for placement of amalgam and composite resins in posterior teeth in children. Forty children, aged seven to nine years old, were selected to participate. Either amalgam or an experimental resin was used to restore the primary and permanent molars. All restorations and sealants were completed under the rubber dam. Each restorative appointment was videotaped with a color video camera mounted on the ceiling. Ninety-six restorative procedures were reviewed and evaluated for the amount of time necessary to accomplish them. The Class I permanent molar composite restoration required 35 percent more insertion and finishing time than did the amalgam.
Assuntos
Resinas Compostas , Amálgama Dentário , Restauração Dentária Permanente/métodos , Dente Pré-Molar , Criança , Forramento da Cavidade Dentária , Humanos , Dente Molar , Distribuição Aleatória , Fatores de Tempo , Gravação de VideoteipeRESUMO
Reports of a mild form of hypophosphatasia have been presented in which the oral findings were the only clinical and radiographic manifestations of the disease. It is important to support the clinical interpretations with laboratory findings in order to make a differential diagnosis from such diseases as Papillon-LeFevre Syndrome and cyclic diseases and noncyclic neutropenia. The term odontohypophosphatasia is suggested in those cases where the dental findings are the predominant manifestations of the disease.