High-temperature Petroleum Reservoir Research Articles

Effect of nano TiO2 and SiO2 on gelation performance of HPAM/PEI gels for high-temperature reservoir conformance improvement

Nanoparticles have been widely used in polymer gel systems in recent years to improve gelation performance under high-temperature reservoir conditions. However, different types of nanoparticles have different effects on their gelation performance, which has been little researched. In this study, the high-temperature gelation performance, chemical structure, and microstructure of polymer gels prepared from two nanomaterials (i.e., nano-SiO2 and nano-TiO2) were measured. The conventional HPAM/PEI polymer gel system was employed as the control sample. Results showed that the addition of nano-TiO2 could significantly enhance the gel strength of HPAM/PEI gel at 80 °C. The gel strength of the enhanced HPAM/PEI gel with 0.1 wt% nano-TiO2 could reach grade I. The system also had excellent high-temperature stability at 150 °C. The enhanced HPAM/PEI gel with 0.02 wt% nano-TiO2 reached the maximum gel strength at 150 °C with a storage modulus (G′) of 15 Pa, which can meet the need for efficient plugging. However, the nano-SiO2 enhanced HPAM/PEI polymer gel system showed weaker gel strength than that with nano-TiO2 at both 80 and 150 °C with G′ lower than 5 Pa. Microstructures showed that the nano-TiO2 enhanced HPAM/PEI gel had denser three-dimensional (3D) mesh structures, which makes the nano-TiO2 enhanced HPAM/PEI gel more firmly bound to water. The FT-IR results also confirmed that the chemical structure of the nano-TiO2 enhanced HPAM/PEI gel was more thermally stable than nano-SiO2 since there was a large amount of –OH groups on the structure surface. Therefore, nano-TiO2 was more suitable as the reinforcing material for HPAM/PEI gels for high-temperature petroleum reservoir conformance improvement.

Development of re-crosslinkable dispersed particle gels for conformance improvement in extremely high-temperature reservoirs

Micro-scale and nano-scale dispersed gel particles (DPG) are capable of deep migration in oil reservoirs due to their deformability, viscoelasticity, and suitable particle size. Therefore, it has been widely studied and applied in reservoir conformance control in recent years. However, for highly permeable channels, their plugging performance is still limited. In addition, conventional in situ cross-linked polymer gels (ISCPGs) have fast gelation time under extremely high-temperature conditions, which often causes problems such as difficulty in pumping. Therefore, a re-crosslinkable dispersed particle gel (RDPG) system applied for conformance control in highly permeable channels of extremely high-temperature petroleum reservoirs was investigated. The particle size distribution, gelation time, gel strength, injection performance, and performance strength in porous media were investigated using a laser particle size meter, the Sydansk bottle test method, rheometer, and core displacement experiments, respectively. Results show that the RDPG suspension can be stable for more than 6 months at room temperature with storage modulus G ′ much lower than 10 Pa. It can pass through the pore throat by elastic deformation effect and does not cause strong blockage. Moreover, it can undergo re-crosslinking reaction at 150 °C to form a strong bulk gel. The gel strength G ′ of re-crosslinked RDPG can be as high as 69.3 Pa, which meets the strength requirement of conformance control. The RDPG suspension has the properties of easy injection, and it also has strong plugging, and high-temperature resistance after re-crosslinked in the core, which can be a very promising material for conformance improvement in extremely high-temperature reservoirs.

Characteristics of microbiota, core sulfate-reducing taxa and corrosion rates in production water from five petroleum reservoirs in China

Microbial diversity and activities in petroleum reservoir systems can be altered by water-flooding operation, but the current understanding of the mechanism for such changes in microbial composition characteristics and community is inadequate. In this study, microbial communities especially functional groups in production water from five petroleum reservoirs in China were investigated by chemical and molecular biological analyses. The dominant and core phyla in the five oil reservoirs were Proteobacteria, Deferribacterota, Firmicutes, Desulfobacterota, Euryarchaeota and Thermoplasmatota. At the genus level, the dominant taxa in each petroleum reservoir were different, and not all of the dominant genera were the core members across the five oil reservoirs. The microbiologically influenced corrosion (MIC) were investigated for the functional groups in each production water. The corrosion rates in production water were higher than controls with a positive correlation to the abundances of sulfate-reducing prokaryotes (SRP). The SRP diversity based on the aprA and dsrA gene analysis showed that obvious differences were evident between onshore (JS, SL, DQ and XJ) and offshore (BS) oilfields. The core SRP taxa in onshore oilfields were Desulfomicrobium and Desulfovibrio, also with Desulfotomaculum in medium/low-temperature oil reservoirs (DQ and XJ), but in high-temperature petroleum reservoirs (JS, BS and SL), Archaeoglobus, Thermodesulfobacterium and Thermodesulfovibrio were the core groups. Statistical analysis indicated that temperature, electron acceptors and donors showed significant influence on the SRP community. This research reveals the characteristics of microbial and functional community as well as their interaction mechanism on corrosion in petroleum reservoir environments, and will improve industrial bio-control and management of MIC in oilfields.

Dominant and Active Methanogens in the Production Waters From a High-Temperature Petroleum Reservoir by DNA- and RNA-Based Analysis

Methane metabolism in deep subsurface petroleum reservoirs is of paramount interest in the global biogeochemical cycle of carbon. Methanogenesis in such habitats is driven mostly by methanogens in syntrophic association with bacteria. In the present study, methanogenic communities in production water samples from six wells of a high-temperature petroleum reservoir were analyzed based on both genomic 16S rDNA and metabolically active 16S rRNA. The PCR-amplified mcrA gene analysis showed that Methanosaeta (26%) and Methanomassiliicoccus (56%) were separately the dominant members in sample W2_71 and W9_18 at the DNA level. In comparison, the RNA-based analysis showed that Methanosaeta (63 ∼ 83%) followed by Methanolinea (16 ∼ 23%) were the most active methanogens, which were different from the communities of genomic DNA. While several lines of studies indicated that CO2-reducing methanogens of the genus Methanothermobacter was the most frequently detected phylotype in deep-subsurface petroleum reservoirs. Redundancy analysis (RDA) showed the possible correlation between active methanogens (Methanosaeta) and environmental factors (CO3 2-). The datasets indicated the importance of investigating methanogenic community by integrating DNA- and RNA-based approaches. These results provide new insight into active methanogens in high-temperature petroleum reservoirs, and promote a comprehensive understanding of methanogens as well as their potential methanogenic pathways in such environments.

Effect of Temperature on Stiffness of Sandstones from the Deep North Sea Basin

Development of high-pressure, high-temperature (HPHT) petroleum reservoirs situated at depths exceeding 5 km and in situ temperature of 170 °C increases the demand for theories and supporting experimental data capable of describing temperature effects on rock stiffness. With the intention of experimentally investigating temperature effects on stiffness properties, we investigated three sandstones from the deep North Sea Basin. As the North Sea Basin is presently undergoing substantial subsidence, we assumed that studied reservoir sandstones have never experienced higher temperature than in situ. We measured ultrasonic velocities in a low- and high-stress regime, and used mass density and stress–strain curves to derive, respectively, dynamic and static elastic moduli. We found that in both regimes, the dry sandstones stiffens with increasing testing temperature and assign expansion of minerals as a controlling mechanism. In the low-stress regime with only partial microcrack closure, we propose closure of microcracks as the stiffening mechanism. In the high-stress regime, we propose that thermal expansion of constituting minerals increases stress in grain contacts when the applied stress is high enough for conversion of thermal strain to thermal stress, thus leading to higher stiffness at in situ temperature. We then applied an extension of Biot’s effective stress equation including a non-isothermal term from thermoelastic theory and explain test results by adding boundary conditions to the equations.

The newly proposed TACK and DPANN archaea detected in the production waters from a high-temperature petroleum reservoir

Revealing the diversity and distribution of archaea is basically crucial to understanding their ecological functions in subsurface petroleum reservoir ecosystems. However, the knowledge about the abundance and distribution of newly proposed archaea (e.g. TACK and DPANN superphyla) in such environments is still limited. In the present work, archaeal communities from five production wells of a high-temperature petroleum reservoir were characterized by high-throughput sequencing. The outcome showed that in the five samples over 98% of archaeal sequences were affiliated to Euryarchaeota, and the rest belonged to newly proposed archaeal phyla (Thaumarchaeota, Verstraetearchaeota, Bathyarchaeota, Aigarchaeota and Woesearchaeota). Based on the defined criteria of rare taxa (<0.1%), OTUs affiliated within Bathyarchaeota, Thaumarchaeota and Woesearchaeota were mostly present as the rare biosphere in the samples. The archaeal communities were significantly shaped by different geochemical parameters of the production waters from the petroleum reservoir. The co-occurrence network analysis revealed the potential syntrophic interactions among the archaea themselves in the subterrestrial environments. Our results indicate that the newly proposed archaea are ubiquitous, also present in the petroleum reservoirs, where they contribute to the ecosystem diversity and play potential roles in the biogeochemical cycle of carbon. This work also provides an overall understanding of the identity, ecology, and functional diversity of newly proposed archaea in petroleum reservoirs.

Bioconversion Pathway of CO2 in the Presence of Ethanol by Methanogenic Enrichments from Production Water of a High-Temperature Petroleum Reservoir

Transformation of CO2 in both carbon capture and storage (CCS) to biogenic methane in petroleum reservoirs is an attractive and promising strategy for not only mitigating the greenhouse impact but also facilitating energy recovery in order to meet societal needs for energy. Available sources of petroleum in the reservoirs reduction play an essential role in the biotransformation of CO2 stored in petroleum reservoirs into clean energy methane. Here, the feasibility and potential on the reduction of CO2 injected into methane as bioenergy by indigenous microorganisms residing in oilfields in the presence of the fermentative metabolite ethanol were assessed in high-temperature petroleum reservoir production water. The bio-methane production from CO2 was achieved in enrichment with ethanol as the hydrogen source by syntrophic cooperation between the fermentative bacterium Synergistetes and CO2-reducing Methanothermobacter via interspecies hydrogen transfer based upon analyses of molecular microbiology and stable carbon isotope labeling. The thermodynamic analysis shows that CO2-reducing methanogenesis and the methanogenic metabolism of ethanol are mutually beneficial at a low concentration of injected CO2 but inhibited by the high partial pressure of CO2. Our results offer a potentially valuable opportunity for clean bioenergy recovery from CCS in oilfields.

Methanogenic degradation of branched alkanes in enrichment cultures of production water from a high-temperature petroleum reservoir.

Branched alkanes are important constituents of crude oil and are usually regarded as resistant to microbial degradation, resulting in little knowledge of biochemical processes involved in anaerobic branched alkanes biodegradation. Here, we initiated an incubation study by amendment of iso-C9 (2-methyl, 3-methyl, and 4-methyloctane) as substrates for methanogenic degradation in production water from a high-temperature petroleum reservoir. Over an incubation period of 367days, significant methanogenesis was observed in samples amended with these branched alkanes. The strong methanogenic activity only observed in iso-C9 amendments suggested the presence of microbial transformation from iso-alkanes into methane. GC-MS-based examination of the original production water identified an intermediate tentatively to be iso-C9-like alkylsuccinate, but was not detected in the enrichment cultures, combined with the successful amplification of assA functional gene in inoculating samples, revealing the ability of anaerobic biodegradation of iso-C9 via fumarate addition pathway. Microorganisms affiliated with members of the Firmicutes, Synergistetes, and methanogens of genus Methanothermobacter spp. were highly enriched in samples amended with iso-C9. The co-occurrence of known syntrophic acetate oxidizers Thermoacetogenium spp. and Methanothermobacter spp. (known hydrogenotrophic methanogens) indicates a potential syntrophic acetate oxidation associated with the methanogenic biodegradation of iso-C9. These results provide some useful information on the potential biodegradation of branched alkanes via methanogenesis and also suggest that branched alkanes are likely activated via fumarate addition in high-temperature petroleum reservoirs.

Conductive Iron Oxides Promote Methanogenic Acetate Degradation by Microbial Communities in a High-Temperature Petroleum Reservoir.

Supplementation with conductive magnetite particles promoted methanogenic acetate degradation by microbial communities enriched from the production water of a high-temperature petroleum reservoir. A microbial community analysis revealed that Petrothermobacter spp. (phylum Deferribacteres), known as thermophilic Fe(III) reducers, predominated in the magnetite-supplemented enrichment, whereas other types of Fe(III) reducers, such as Thermincola spp. and Thermotoga spp., were dominant under ferrihydrite-reducing conditions. These results suggest that magnetite induced interspecies electron transfer via electric currents through conductive particles between Petrothermobacter spp. and methanogens. This is the first evidence for possible electric syntrophy in high-temperature subsurface environments.

Down-hole isolation towards high-temperature reservoir using packing elements with swellable thermo-plastic vulcanizates

The well completion and fracturing towards deep unconventional high-temperature (HT) petroleum or natural gas reservoirs is considerably strict to the packer especially packing elements. However, existing packing elements including swellable packers usually are made from Hydrogenated Nitrile (HNBR) or Fluorine rubber (FKM) with drawbacks of great expense and difficult tripping into the horizontal wellbore. This paper proposes a compact isolating solution using swellable Thermo-plastic Vulcanizates (TPVs), which is prepared by blending HNBR, low-cost Polyamide66 (PA66) and Porous Super Absorbent Resin (PSAR) with enhanced nanoparticles. The TPVs were characterized by experiments and the system with Plastic/Elastomer Ratio (PER) of 45:55, tensile strength of 18.6 MPa and elongation at break of 635% upon aging (150 °C) was qualified for the packing element material. A novel enhanced packing element is put forward with corrugated-profile structure to address large-size and over-extrusion issues. The numerical study on packer components was conducted based on TPV constitutive model. The prototype with element length of 2.5–2.6 m was validated in the lab and rated as the sealing of more than 70 MPa. An optional disintegrating casing is adopted to avoid the premature damage risk of packers. For the field trial, the multistage fracturing tubular with improved packers was deployed into the horizontal open hole without severe pipe stuck. The fracturing operation was successfully performed and all packers functioned normally with the maximum pressure differential of 73 MPa. It concludes that the new solution exhibited high strength, heat resistance and structure integrity with low cost over the traditional packers towards HT environment.

Evaluating the potential of indigenous methanogenic consortium for enhanced oil and gas recovery from high temperature depleted oil reservoir

In past years, lots of research has been focused on the indigenous bacteria and their mechanisms, which help in enhanced oil recovery. Most of the oil wells in Indian subcontinent have temperature higher than 60 °C. Also, the role of methanogenic consortia from high temperature petroleum reservoir for enhanced oil recovery (EOR) has not been explored much. Hence, in the present study methanogens isolated from thermophilic oil wells (70 °C) were evaluated for enhanced oil recovery. Methane gas is produced by methanogens, which helps in oil recovery from depleted oil wells through reservoir re-pressurization and also can be recovered from reservoir along with crude oil as alternative energy source. Therefore, in this study indigenous methanogenic consortium (TERIL146) was enriched from high temperature oil reservoir showing (12 mmol/l) gas production along with other metabolites. Sequencing analysis revealed the presence of Methanothermobacter sp., Thermoanaerobacter sp., Gelria sp. and Thermotoga sp. in the consortium. Furthermore, the developed indigenous consortium TERIL146 showed 8.3% incremental oil recovery in sandpack assay. The present study demonstrates successful recovery of both oil and energy (gas) by the developed indigenous methanogenic consortium TERIL146 for potential application in thermophilic depleted oil wells of Indian subcontinent.

Different Diversity and Distribution of Archaeal Community in the Aqueous and Oil Phases of Production Fluid From High-Temperature Petroleum Reservoirs.

To get a better knowledge on how archaeal communities differ between the oil and aqueous phases and whether environmental factors promote substantial differences on microbial distributions among production wells, we analyzed archaeal communities in oil and aqueous phases from four high-temperature petroleum reservoirs (55–65°C) by using 16S rRNA gene based 454 pyrosequencing. Obvious dissimilarity of the archaeal composition between aqueous and oil phases in each independent production wells was observed, especially in production wells with higher water cut, and diversity in the oil phase was much higher than that in the corresponding aqueous phase. Statistical analysis further showed that archaeal communities in oil phases from different petroleum reservoirs tended to be more similar, but those in aqueous phases were the opposite. In the high-temperature ecosystems, temperature as an environmental factor could have significantly affected archaeal distribution, and archaeal diversity raised with the increase of temperature (p < 0.05). Our results suggest that to get a comprehensive understanding of petroleum reservoirs microbial information both in aqueous and oil phases should be taken into consideration. The microscopic habitats of oil phase, technically the dispersed minuscule water droplets in the oil could be a better habitat that containing the indigenous microorganisms.

In Situ Surface Decorated Polymer Microsphere Technology for Enhanced Oil Recovery in High-Temperature Petroleum Reservoirs

Polymer microspheres have been applied for petroleum reservoir enhanced oil recovery (EOR) in the past decade because they can overcome some drawbacks inherent in in situ polymer gel systems. A novel in situ surface decorated polymer microsphere technology was developed for chemical EOR in high-temperature reservoirs. The swelling performance of the conventional polymer microspheres at room temperature was systematically analyzed and verified by an environmental scanning electron microscope. Their swelling and degradation mechanisms at a high temperature (150 °C) were also examined. To improve the long-term thermal stability of the polymer microsphere, different concentrations of polyethylenimine (PEI) were used as an in situ surface decorating agent. The decorated microspheres remained stable at 150 °C for more than three months, and thermogravimetric analysis indicated that the in situ surface decorated polymer microspheres could remain stable at temperatures up to 310 °C. PEI-decorated 3D network struc...

Polymer Gel Systems for Water Management in High-Temperature Petroleum Reservoirs: A Chemical Review

Polymer gel systems as water management materials have been widely used in recent years for enhanced oil recovery applications. However, most polymer gel systems are limited in their ability to withstand the harsh environments of high temperature and high salinity. Those polymer gel systems that can handle high-temperature excessive water treatments are reviewed in this paper and categorized into three major types: in situ cross-linked polymer gels, preformed gels, and foamed gels. Future directions for the development of polymer gel systems for high-temperature conditions are recommended. For excessive water management with temperatures from 80 to 120 °C, current polymer systems are substantially adequate. Polymer gel systems composed of partially hydrolyzed polyacrylamide (HPAM)/chromium can be combined with nanoparticle technology to elongate their gelation time and reduce the adsorption of chromium ions in the formation. Phenolic resin cross-linker systems have reasonable gelation times and gel streng...

Iron oxides alter methanogenic pathways of acetate in production water of high-temperature petroleum reservoir.

Acetate is a key intermediate in anaerobic crude oil biodegradation and also a precursor for methanogenesis in petroleum reservoirs. The impact of iron oxides, viz. β-FeOOH (akaganéite) and magnetite (Fe3O4), on the methanogenic acetate metabolism in production water of a high-temperature petroleum reservoir was investigated. Methane production was observed in all the treatments amended with acetate. In the microcosms amended with acetate solely about 30% of the acetate utilized was converted to methane, whereas methane production was stimulated in the presence of magnetite (Fe3O4) resulting in a 48.34% conversion to methane. Methane production in acetate-amended, β-FeOOH (akaganéite)-supplemented microcosms was much faster and acetate consumption was greatly improved compared to the other conditions in which the stoichiometric expected amounts of methane were not produced. Microbial community analysis showed that Thermacetogenium spp. (known syntrophic acetate oxidizers) and hydrogenotrophic methanogens closely related to Methanothermobacter spp. were enriched in acetate and acetate/magnetite (Fe3O4) microcosms suggesting that methanogenic acetate metabolism was through hydrogenotrophic methanogenesis fueled by syntrophic acetate oxidizers. The acetate/β-FeOOH (akaganéite) microcosms, however, differed by the dominance of archaea closely related to the acetoclastic Methanosaeta thermophila. These observations suggest that supplementation of β-FeOOH (akaganéite) accelerated the production of methane further, driven the alteration of the methanogenic community, and changed the pathway of acetate methanogenesis from hydrogenotrophic methanogenesis fueled by syntrophic acetate oxidizers to acetoclastic.

Dominance of Desulfotignum in sulfate-reducing community in high sulfate production-water of high temperature and corrosive petroleum reservoirs

Petroleum reservoirs souring and pipelines corrosion are severe in Jiangsu Oilfield of China, and microorganisms have a major role in the related problems. This study revealed the microbial diversity and composition of both bacteria and archaea by using 16S rRNA gene clone library method, and those of sulfate-reducing prokaryotes (SRP) by dissimilatory sulfate reductase α-subunit encoding gene (dsr) clone library in two different samples of high temperature petroleum reservoirs containing high concentration of sulfate and with known corrosion. In addition, the abundance of bacteria and SRP in the samples was quantified by real-time PCR assays based on 16S rRNA and dsr genes. The results showed that both production water samples from Wei 2-53 and Wei 11-7 wells exhibited very rich bacterial diversity, and both Gammaproteobacteria and Alphaproteobacteria were the main abundant ones. Thioalkalivibrio-related species belonging to Gammaproteobacteria were also observed in both of them. Methanomicrobia, Archaeoglobi and Thermococci were common archaea in these samples, with Archaeoglobus as the dominant genus in both of them. The dsrA libraries analysis showed that a low diversity of sulfidogenic communities with Desulfotignum spp. as the most dominant SRP in the samples. The data reported here enhance our knowledge on microbial community and abundance including SRP in high temperature and corrosive reservoirs, providing a better basis for further research on and management control of reservoir souring and biocorrosion in oil production systems.

Bacteria in the injection water differently impacts the bacterial communities of production wells in high-temperature petroleum reservoirs.

Water flooding is widely used for oil recovery. However, how the introduction of bacteria via water flooding affects the subsurface ecosystem remains unknown. In the present study, the distinct bacterial communities of an injection well and six adjacent production wells were revealed using denaturing gradient gel electrophoresis (DGGE) and pyrosequencing. All sequences of the variable region 3 of the 16S rRNA gene retrieved from pyrosequencing were divided into 543 operational taxonomic units (OTUs) based on 97% similarity. Approximately 13.5% of the total sequences could not be assigned to any recognized phylum. The Unifrac distance analysis showed significant differences in the bacterial community structures between the production well and injection water samples. However, highly similar bacterial structures were shown for samples obtained from the same oil-bearing strata. More than 69% of the OTUs detected in the injection water sample were absent or detected in low abundance in the production wells. However, the abundance of two OTUs reached as high as 17.5 and 26.9% in two samples of production water, although the OTUs greatly varied among all samples. Combined with the differentiated water flow rate measured through ion tracing, we speculated that the transportation of injected bacteria was impacted through the varied permeability from the injection well to each of the production wells. Whether the injected bacteria predominate the production well bacterial community might depend both on the permeability of the strata and the reservoir conditions.

Evaluation of microbial community composition in thermophilic methane-producing incubation of production water from a high-temperature oil reservoir

Investigation of petroleum microbes is fundamental for the development and utilization of oil reservoirs’ microbial resources, and also provides great opportunities for research and development of bio-energy. Production water from a high-temperature oil reservoir was incubated anaerobically at 55°C for more than 400 days without amendment of any nutrients. Over the time of incubation, about 1.6 mmol of methane and up to 107 μ mol of hydrogen (H2) were detected in the headspace. Methane formation indicated that methanogenesis was likely the predominant process in spite of the presence of 23.4 mM in the production water. Microbial community composition of the incubation was characterized by means of 16S rRNA gene clone libraries construction. Bacterial composition changed from Pseudomonales as the dominant population initially to Hydrogenophilales-related microorganisms affiliated to Petrobacter spp. closely. After 400 days of incubation, other bacterial members detected were related to Anareolineales, β-, γ-, and δ-Proteobacteria. The archaeal composition of the original production water was essentially composed of obligate acetoclastic methanogens of the genus Methanosaeta, but the incubation was predominantly composed of CO2-reducing methanogens of the genus Methanothermobacter and Crenarchaeotes-related microorganisms. Our results suggest that methanogenesis could be more active than expected in oil reservoir environments and methane formation from CO2-reduction played a significant role in the methanogenic community. This conclusion is consistent with the predominant role played by H2-oxidizing methanogens in the methanogenic conversion of organic matter in high-temperature petroleum reservoirs.

Functional genes (dsr) approach reveals similar sulphidogenic prokaryotes diversity but different structure in saline waters from corroding high temperature petroleum reservoirs

Oil reservoirs and production facilities are generally contaminated with H2S resulting from the activity of sulphidogenic prokaryotes (SRP). Sulphidogenesis plays a major role in reservoir souring and microbial influenced corrosion in oil production systems. In the present study, sulphidogenic microbial diversity and composition in saline production fluids retrieved from three blocks of corroding high temperature (79 ~ 95 °C) oil reservoirs with high sulfate concentrations were investigated by phylogenetic analyses of gene fragments of the dissimilatory sulfite reductase (dsr). Analysis of dsr gene fragments revealed the presence of several clusters of sulphidogenic prokaryotes that cover the orders Desulfovibrionales (Desulfovibrio, Desulfomicrobium thermophilum), Desulfobacterales (Desulfobacterium, Desulfosarcina, Desulfococcus, Desulfotignum, Desulfobotulus, Desulfobulbus), Syntrophobacterales (Desulfacinum, Thermodesulforhabdus, Desulforhabdus), Clostridiales (Desulfotomaculum) and Archaeoglobales (Archaeoglobus); among which sequences affiliated to members of Desulfomicrobium, Desulfotomaculum and Desulfovibrio appeared to be the most encountered genera within the three blocks. Collectively, phylogenetic and non-metric multidimensional scaling analyses indicated similar but structurally different sulphidogenic prokaryotes communities within the waters retrieved from the three Blocks. This study show the diversity and composition of sulphidogenic prokaryotes that may play a role in the souring mediated corrosion of the oilfield and also provides a fundamental basis for further investigation to control oil reservoir souring and corrosion of pipelines and topside installations.

Molecular analysis of the microbial community structures in water-flooding petroleum reservoirs with different temperatures

Abstract. Analyses of microbial communities from six water-flooding petroleum reservoirs at temperatures from 21 to 63 °C by 16S rRNA gene clone libraries indicates the presence of physiologically diverse and temperature-dependent microorganisms in these subterrestrial ecosystems. In samples originating from high-temperature petroleum reservoirs, most of the archaeal sequences belong to thermophiles affiliated with members of the genera Thermococcus, Methanothermobacter and the order Thermoplasmatales, whereas bacterial sequences predominantly belong to the phyla Firmicutes, Thermotogae and Thermodesulfobacteria. In contrast to high-temperature petroleum reservoirs, microorganisms belonging to the Proteobacteria, Methanobacteriales and Methanomicrobiales were the most encountered in samples collected from low-temperature petroleum reservoirs. Canonical correspondence analysis (CCA) revealed that temperature, mineralization, ionic type as well as volatile fatty acids showed correlation with the microbial community structures, in particular members of the Firmicutes and the genus Methanothermobacter showed positive correlation with temperature and the concentration of acetate. Overall, these data indicate the large occurrence of hydrogenotrophic methanogens in petroleum reservoirs and imply that acetate metabolism via syntrophic oxidation may represent the main methanogenic pathway in high-temperature petroleum reservoirs.