Characterization of Crude Oil, Formation Water, and Fluid Inclusions of Hydrocarbon-Bearing Strata and Their Hydrocarbon Geological Significance in the Wuliyasitai Southern Sub-sag of the Erlian Basin, China.

The hydrocarbon-bearing inclusions, formation water, and crude oil contain a wealth of information regarding the process of accumulation of oil and gas. Their research has been one of the hotspots in the field of oil and gas geology. Chemical analysis data was systematically employed for the first time to identify the properties of liquid fluids in the oil-bearing system of the Wuliyasitai southern sag in the Erlian Basin. A biased lacustrine algal input was shown by the stable carbon isotopes (δ13C) of whole hydrocarbons, and the morphological characteristics of n-alkanes, isoprenoids, steranes, and terpenes were examined by gas chromatography-mass spectrometry. The δ13C values were determined by the salinity of the sedimentary water body and input of land-sourced materials. The signatures of the n-alkanes' molar fraction arrangement suggest that water washing, crystallization, and wax precipitation are regular occurrences in oil samples. The salinity of formation water and the proportion of characteristic biomarkers (gammacerane, ß-carotene) demonstrate that the salinity of the ancient water body ranges from fresh water to brackish water. The correlation between the stratigraphic water's characteristic coefficients and the total dissolved solids (TDS) is strong, particularly for the desulfurization coefficient, which illustrates a better hydrocarbon storage environment when TDS is >6 g/L. The metamorphic coefficients demonstrate that the existing reservoir preservation circumstances are not optimal, and the TDS and concentration degree of formation water are positively connected to the increasing depth, indicating poor longitudinal connectivity. The influence of atmospheric water infiltration is responsible for the fluid inclusions' temperatures of homogenization (60 °C). However, due to deep burial, crude oil has not undergone secondary significant biodegradation despite the percolation of atmospheric water. Besides, the distribution of reservoirs is highly correlated with formation water parameters such as the TDS, which can provide scientific guidance for further exploration of oil and gas in the study area or even in the Erlian Basin.

Geochemical Characteristics of Three Oil Families and Their Possible Source Rocks in the Sub-Sag A of Weixinan Depression, Beibuwan Basin, Offshore South China Sea.

Three oil families from the sub-sag A of the Weixinan Depression are identified by integrated analysis of physical properties, stable carbon isotopes, and gas chromatography-mass spectrometry (GC-MS). Their similarities and differences in relative thermal maturities, depositional environments, and biological sources of organic matter (OM) are investigated. A possible oil-source correlation of this area is established. Group A1 oils, defined as low-maturity oils, are characterized by high density and high viscosity. They contain more terrigenous OM deposited in a freshwater environment with unstratified water columns reflected by a relatively high terrestrial/aquatic ratio and Pr/Ph values, low abundance of C30 4-methlysteranes, and low δ13C values. They are derived from the upper hydrocarbon supply combination. Group A2 oils are characterized by moderate density and viscosity and medium stable carbon isotope values. This group of oils has lower terrestrial/aquatic ratios and Pr/Ph values and a medium concentration of C30 4-methlysteranes and δ13C values, suggesting that the oils are derived from the shales which have more contribution from the algal input and are formed in a weakly oxidizing environment. They are a mixture generated from the source rocks in the middle and lower hydrocarbon supply combination. Groups A3 oils, defined as light oils, have low density and viscosity. The geochemical data of the A3 oils, including a less-negative stable carbon isotope, high abundance of C30 4-methylsteranes, low Pr/Ph values, and highest Ts/(Ts + Tm) ratios (Ts represents C27 18α(H)-22,29,30-trisnorneohopane and Tm represents C27 17α(H)-22,29,30-trisnorhopane), suggest that they are generated from the source rocks deposited in a subanoxic environment with the large input of dinoflagellates. The A3 oils are generated from the shales from the lower hydrocarbon supply combination. The oil-source correlation results can be further supported by the distribution of faults and structural ridge as the migration channel of petroleum developed around the sub-sag A.

Tracking alterations of alkyl side chains of N1 species in heavy crude oil after anaerobic biodegradation with negative-ion electrospray ionization coupled with high-field Fourier transform ion cyclotron resonance mass spectrometry.

RATIONALE: Heteroatomic compounds are relatively abundant and believed to be bio-resistant in heavy crude oils. However, few studies have focused on the biodegradation of these heteroatomic compounds. METHODS: Heteroatoms, especially N1 species, in a blank crude oil and in three treated oils co-incubated with anaerobic sulfate-reducing bacteria, nitrate-reducing bacteria and fermentative consortia cultures were detected using negative-ion electrospray ionization coupled with high-field Fourier transform ion cyclotron resonance mass spectrometry. RESULTS: The relative abundance of N1 species in the three treated oils decreased, while the relative abundance of O2 species increased. Remarkably, the relative abundances of N1 species with low carbon number increased and those with higher carbon number decreased. CONCLUSIONS: These results revealed that the anaerobic biodegradations of heavy crude oil occurred. With direct evidences, the degradations of alkyl side chains of N1 species by the anaerobic microbes could be deduced.

Isolation and characterization of a crude oil degrading bacteria from formation water: comparative genomic analysis of environmental Ochrobactrum intermedium isolate versus clinical strains.

In this study, we isolated an environmental clone of Ochrobactrum intermedium, strain 2745-2, from the formation water of Changqing oilfield in Shanxi, China, which can degrade crude oil. Strain 2745-2 is aerobic and rod-shaped with optimum growth at 42 °C and pH 5.5. We sequenced the genome and found a single chromosome of 4 800 175 bp, with a G+C content of 57.63%. Sixty RNAs and 4737 protein-coding genes were identified: many of the genes are responsible for the degradation, emulsification, and metabolizing of crude oil. A comparative genomic analysis with related clinical strains (M86, 229E, and LMG3301(T)) showed that genes involved in virulence, disease, defense, phages, prophages, transposable elements, plasmids, and antibiotic resistance are also present in strain 2745-2.

High quality genome sequence and description of Enterobacter mori strain 5-4, isolated from a mixture of formation water and crude-oil.

Enterobacter mori strain 5-4 is a Gram-negative, motile, rod shaped, and facultatively anaerobic bacterium, which was isolated from a mixture of formation water (also known as oil-reservior water) and crude-oil in Karamay oilfield, China. To date, there is only one E. mori genome has been sequenced and very little knowledge about the mechanism of E. mori adapted to the petroleum reservoir. Here, we report the second E. mori genome sequence and annotation, together with the description of features for this organism. The 4,621,281 bp assembly genome exhibits a G + C content of 56.24% and contains 4,317 protein-coding and 65 RNA genes, including 5 rRNA genes.

Permanent draft genome sequence of Bacillus flexus strain T6186-2, a multidrug-resistant bacterium isolated from a deep-subsurface oil reservoir.

Previous studies suggest that antibiotic resistance genes have an ancient origin, which is not always linked to the use of antibiotics but can be enhanced by human activities. Bacillus flexus strain T6186-2 was isolated from the formation water sample of a deep-subsurface oil reservoir. Interestingly, antimicrobial susceptibility testing showed that this strain is susceptible to kanamycin, however, resistant to ampicillin, erythromycin, gentamicin, vancomycin, fosfomycin, fosmidomycin, tetracycline and teicoplanin. To explore our knowledge about the origins of antibiotic resistance genes (ARGs) in the relatively pristine environment, we sequenced the genome of B. flexus strain T6186-2 as a permanent draft. It represents the evidence for the existence of a reservoir of ARGs in nature among microbial populations from deep-subsurface oil reservoirs.

Genomovar assignment of Pseudomonas stutzeri populations inhabiting produced oil reservoirs.

Oil reservoirs are specific habitats for the survival and growth of microorganisms in general. Pseudomonas stutzeri which is believed to be an exogenous organism inoculated into oil reservoirs during the process of oil production was detected frequently in samples from oil reservoirs. Very little is known, however, about the distribution and genetic structure of P. stutzeri in the special environment of oil reservoirs. In this study, we collected 59 P. stutzeri 16S rRNA gene sequences that were identified in 42 samples from 25 different oil reservoirs and we isolated 11 cultured strains from two representative oil reservoirs aiming to analyze the diversity and genomovar assignment of the species in oil reservoirs. High diversity of P. stutzeri was observed, which was exemplified in the detection of sequences assigned to four known genomovars 1, 2, 3, 20 and eight unknown genomic groups of P. stutzeri. The frequent detection and predominance of strains belonging to genomovar 1 in most of the oil reservoirs under study indicated an association of genomovars of P. stutzeri with the oil field environments.

Microbial diversity in long-term water-flooded oil reservoirs with different in situ temperatures in China.

Water-flooded oil reservoirs have specific ecological environments due to continual water injection and oil production and water recycling. Using 16S rRNA gene clone library analysis, the microbial communities present in injected waters and produced waters from four typical water-flooded oil reservoirs with different in situ temperatures of 25 °C, 40 °C, 55 °C and 70 °C were examined. The results obtained showed that the higher the in situ temperatures of the oil reservoirs is, the less the effects of microorganisms in the injected waters on microbial community compositions in the produced waters is. In addition, microbes inhabiting in the produced waters of the four water-flooded oil reservoirs were varied but all dominated by Proteobacteria. Moreover, most of the detected microbes were not identified as indigenous. The objective of this study was to expand the pictures of the microbial ecosystem of water-flooded oil reservoirs.

Impact of an indigenous microbial enhanced oil recovery field trial on microbial community structure in a high pour-point oil reservoir.

Based on preliminary investigation of microbial populations in a high pour-point oil reservoir, an indigenous microbial enhanced oil recovery (MEOR) field trial was carried out. The purpose of the study is to reveal the impact of the indigenous MEOR process on microbial community structure in the oil reservoir using 16Sr DNA clone library technique. The detailed monitoring results showed significant response of microbial communities during the field trial and large discrepancies of stimulated microorganisms in the laboratory and in the natural oil reservoir. More specifically, after nutrients injection, the original dominant populations of Petrobacter and Alishewanella in the production wells almost disappeared. The expected desirable population of Pseudomonas aeruginosa, determined by enrichment experiments in laboratory, was stimulated successfully in two wells of the five monitored wells. Unexpectedly, another potential population of Pseudomonas pseudoalcaligenes which were not detected in the enrichment culture in laboratory was stimulated in the other three monitored production wells. In this study, monitoring of microbial community displayed a comprehensive alteration of microbial populations during the field trial to remedy the deficiency of culture-dependent monitoring methods. The results would help to develop and apply more MEOR processes.

Molecular biologic techniques applied to the microbial prospecting of oil and gas in the Ban 876 gas and oil field in China.

Currently, molecular biologic techniques achieve a great development in studies of soil samples. The objective of this research is to improve methods for microbial prospecting of oil and gas by applying culture-independent techniques to soil sampled from above a known oil and gas field. Firstly, the community structure of soil bacteria above the Ban 876 Gas and Oil Field was analyzed based on 16S rRNA gene clone libraries. The soil bacteria communities were consistently different along the depth; however, Chloroflexi and Gemmatimonadetes were predominant and methanotrophs were minor in both bacteria libraries (DGS1 and DGS2). Secondly, the numbers of methane-oxidizing bacteria, quantified using a culture-dependent procedure and culture-independent group-specific real-time PCR (RT-PCR), respectively, were inconsistent with a quantify variance of one or two orders of magnitude. Special emphasis was given to the counting advantages of RT-PCR based on the methanotrophic pmoA gene. Finally, the diversity and distribution of methanotrophic communities in the soil samples were analyzed by constructing clone libraries of functional gene. All 508-bp inserts in clones phylogenetically belonged to the methanotrophic pmoA gene with similarities from 83% to 100%. However, most of the similarities were below 96%. Five clone libraries of methanotrophs clearly showed that the anomalous methanotrophs (Methylosinus and Methylocystis) occupy the studied area.