8. Petroleum: from formation to microbiology

Abstract

Economic petroleum accumulations result from the migration in the lithosphere of hydrocarbons formed by the maturation of kerogen. This is a long-term process mainly controlled by temperature and pressure conditions that depend on the geological evolution of the hosting sedimentary basin.Cultural and molecular approaches both reveal that petroleum reservoirs are inhabited by a wide range of mesophilic and thermophilic/hyperthermophilic anaerobic microorganisms able to ferment or oxidize their substrates. Among them sulfatereducing prokaryotes and methanoarchaea are recognized as important contributors to the geomicrobiology of these ecosystems because of their hydrogenotrophic and/or acetoclastic nature. Some of them together with members of the Thermotogales, and other fermentative prokaryotes are considered as indigenous to oil reservoirs. Taking into account the high microbial metabolic diversity existing in oil reservoirs, we may expect the activity of many of these oilfield microorganisms to be of interest in enhancing oil recovery in the next future. Petroleum formationPetroleum is a general term for a mixture of hydrocarbons that exist naturally on Earth in gaseous (natural gas), liquid (crude oil) and solid (asphalt) states and are characterized by density lower than that of water [1]. Typical compounds of petroleum contain carbon and hydrogen (C H ) with small amounts of oxygen, nitrogen and sulfur.Petroleum occurs generally in sedimentary rocks formed under marine or terrestrial environments and buried in the external envelop of the lithosphere ( Fig. 8.1 (a)). Its complex nature is evidenced by the high numbers (> 1000) of hydrocarbon species that have been identified since petroleum exploitation started in the 19 ℎ century [2]. Under natural conditions, petroleum gas is composed by saturated hydrocarbons (alkanes) with one to three carbon atoms. Petroleum oil is a complex mixture of alkanes with more than four carbon atoms, such as paraffin, cyclo-alkanes and aromatics [3]. Sulfur, nitrogen and oxygen can be present in oil within complex organic molecules such as resins and asphalts. The presence of biomarkers in petroleum (e.g. elements of chlorophyll or cellulose for example) demonstrated the organic origin of oil and gas despite ancient but famous inorganic theories by Porfir'ev [4] and Gold and Soter [5]. Brought to you by | Stockholms Universitet Authenticated Download Date | 8/25/15 7:03 AM Brought to you by | Stockholms Universitet Authenticated Download Date | 8/25/15 7:03 AM 8.2 Petroleum formation | 163Petroleum formation can be considered as a set of physico-chemico-biological processes within the general organic carbon cycle on Earth, from life, built with elementary chemical components (C,H,O,N), to the production of organic matter and its ultimate decomposition into chemical elements taken by life, thus looping the cycle [6]. This cycle operates in the external Earth envelops, under the influence of solar and earth mantel energy, and can be separated in several interacting subcycles wit...

Microbial Degradation Rates of Natural Bitumen

“…A possible explanation are fermenters, which are present in numerous oil reservoirs and play an important role in the overall hydrocarbon degradation. Fermenters often belong to the most abundant microorganisms after incubation of oil, heavy oil, or water from oil reservoirs. ,− Among others, several members of the phylum Chloroflexi , the order Desulfobacterales , the family Deferribacteraceae , or the genus Thermovirga were present in our communities. These microorganisms are either known fermenters or possess at least the ability for hydrocarbons fermentation in oil reservoirs. ,− ,− In addition, many sulfate reducers present in oil reservoirs can also ferment in the absence of sulfate or when sulfate reduction is inhibited .…”

“…Fermenters often belong to the most abundant microorganisms after incubation of oil, heavy oil, or water from oil reservoirs. ,− Among others, several members of the phylum Chloroflexi , the order Desulfobacterales , the family Deferribacteraceae , or the genus Thermovirga were present in our communities. These microorganisms are either known fermenters or possess at least the ability for hydrocarbons fermentation in oil reservoirs. ,− ,− In addition, many sulfate reducers present in oil reservoirs can also ferment in the absence of sulfate or when sulfate reduction is inhibited . Other fermenting microorganisms often live in syntrophic communities by providing metabolites such as hydrogen and acetate to microorganisms like SRB or methanogens ,,, Therefore, it is likely that the remaining carbon and electron equivalents were not evolved as CO 2 but were present as fermentation products.…”

Preservation of ancestral Cretaceous microflora recovered from a hypersaline oil reservoir

“…formation water) in oil fields are rare and may not be accurate for comparison with our study, due to the difference in salinity. However, there are few reports on the predominance of aerobic microorganisms in oil reservoirs that are generally inhabited by strict anaerobes including sulfate-reducers and methanogens 6 7 . The reservoir rock studied here belongs to a cretaceous formation dominated by evaporitic conditions 9 .…”

“…In contrast, there are several examples of isolation from oil reservoirs in literature of bacteria pertaining to the family Halanaerobiaceae ( e.g. Halanaerobium genus) 7 , which have been retrieved only by molecular approaches during the course of this study. In this respect, the novel isolated halophilic anaerobe 37 might have been a microbial remnant of the original microbial community in the sedimentary basin.…”

“…They contain an excess of reduced electron donors (hydrocarbons) but a shortage of electron acceptors ( e.g. , nitrate, oxygen…) and are considered as anaerobic environments 5 6 7 . We characterized the indigenous microbiota of a hypersaline oil reservoir by molecular and cultural analyzes of rock samples, rather than from fluid samples ( e.g.…”