Study on the kinetics of formation process of emulsion of heavy oil and its functional group components.

Enhanced oil recovery (EOR) by in situ formation of oil-in-water emulsion in heavy oil cold production technology has received growing interest from the petroleum industry. We present an experimental study of emulsification of model oils prepared by heavy oil and its functional group compositions dissolved into toluene brought into contact with a surfactant solution. The effects of functional group composition, emulsifier concentration, temperature, pH and stirring speed on the emulsification rate of heavy oil was investigated. A second-order kinetic model characterizing the temporal variation of conductivity during the emulsification has been established. The results show that acidic and amphoteric fractions exhibit higher interfacial activity, larger emulsification rate constant and faster emulsification rate. With the increase of emulsifier concentration, the emulsification rate constant increase to the maximum value at a concentration of 0.05 mol/L before decreasing. Temperature increase benefits the emulsification rate and the activation energy of the emulsification process is 40.28 kJ/mol. Higher pH and stirring speed indicate faster emulsification rate. The heterogeneity of emulsions limits the accuracy of dynamic characterization of the emulsification process and the determination method of emulsification rate has always been controversial. The conductivity method we proposed can effectively evaluates the emulsification kinetics. This paper provides theoretical guidance for an in-depth understanding of the mechanism and application of cold recovery technology for heavy oil.

Influences of long-duration NO exposure on CO2 adsorption on coals: insights into oxy-coal burning flue gas storage in coal reservoirs.

Introducing oxy-coal burning flue gas into coal reservoirs has the advantages of mitigating emissions of CO2, NOx, and SO2, and producing in-situ coalbed methane (CBM). Given the characteristics of the geologic time scale for fluid sequestration, the long-duration NO exposure was conducted for various ranks of coal matrices to access the potential impacts of NO exposure on CO2 storage. Afterwards, the changes in critical physico-chemical properties and adsorbability of various ranks of coal matrices to CO2 because of long-duration NO exposure were revealed. Finally, the implications to implement oxy-coal burning flue gas sequestration in unmineable coal reservoirs with CBM production were indicated. The results demonstrate that the long-duration interaction with NO reduces the number of micro- and meso-pores of various ranks of coals, especially those with diametres below 4.00 nm. Moreover, the long-duration NO exposure reduces the oxygen-containing functional groups while significantly increasing the amine/amide-N for all the coals. The aforementioned alterations in the surface chemistry property imply that the coal matrix is capable of chemically adsorbing NO, thereby achieving its stable storage in target coal reservoirs. Given the electron donor-acceptor interactions between amine/amide-N and CO2, the NO exposure can elevate the CO2 storage capability of various ranks of coals under typical reservoir temperature and pressure. In summary, introducing oxy-coal burning flue gas into coal reservoirs is capable of stably storing critical gaseous pollutants and simultaneously enhancing the CO2 storage potential of coal reservoirs, thereby updating the existing oxy-coal burning technology and CO2 sequestration in unmineable coal reservoirs with the enhanced CBM recovery technology.

Effect of permeability and fractures on oil mobilization of unconventional resources during CO2 EOR using nuclear magnetic resonance.

CO2 EOR (enhanced oil recovery) will be one of main technologies of enhanced unconventional resources recovery. Understanding effect of permeability and fractures on the oil mobilization of unconventional resources, i.e. tight oil, is crucial during CO2 EOR process. Exposure experiments based on nuclear magnetic resonance (NMR) were used to study the interaction between CO2 and tight oil reservoirs in Chang 8 layer of Ordos Basin at 40 °C and 12 MPa. Effect of permeability and fractures on oil mobilization of exposure experiments were investigated for the different exposure time. The oil was mobilized from matrix to the surface of matrix and the oil recovery increased as the exposure time increased. The final oil recovery increased as the core permeability increased in these exposure experiments. Exposure area increased to 1.75 times by fractures resulting in that oil was mobilized faster in the initial stage of exposure experiment and the final oil recovery increased to 1.19 times from 28.8 to 34.2%. This study shows the quantitative results of effect of permeability and fractures on oil mobilization of unconventional resources during CO2 EOR, which will support CO2 EOR design in Chang 8 layer of Ordos Basin.

Energy Conservation and Carbon Flux Distribution During Fermentation of CO or H2/CO2 by Clostridium ljungdahlii.

Both CO and H2 can be utilized as energy sources during the autotrophic growth of Clostridium ljungdahlii. In principle, CO is a more energetically and thermodynamically favorable energy source for gas fermentation in comparison to H2. Therefore, metabolism may vary during growth under different energy sources. In this study, C. ljungdahlii was fed with CO and/or CO2/H2 at pH 6.0 with a gas pressure of 0.1 MPa. C. ljungdahlii primarily produced acetate in the presence of H2 as an energy source, but produced alcohols with CO as an energy source under the same fermentation conditions. A key enzyme activity assay, metabolic flux analysis, and comparative transcriptomics were performed for investigating the response mechanism of C. ljungdahlii under different energy sources. A CO dehydrogenase and an aldehyde:ferredoxin oxidoreductase were found to play important roles in CO utilization and alcohol production. Based on these findings, novel metabolic schemes are proposed for C. ljungdahlii growing on CO and/or CO2/H2. These schemes indicate that more ATP is produced during CO-fermentation than during H2-fermentation, leading to increased alcohol production.

Experimental Study on the Density-Driven Carbon Dioxide Convective Diffusion in Formation Water at Reservoir Conditions.

Density-driven convection, which can accelerate the dissolution rate of carbon dioxide (CO2) in resident brine, is critical for the long-term fate of the injected CO2 permanence and security of CO2 geological storage. Visualization experiments and pressure-volume-temperature (PVT) testing were conducted to investigate the influence from gravitational convection. For investigate gravitational instabilities and convective diffusion, we designed a Hele-Shaw cell rated to 70 MPa and Rayleigh number of 346 to conduct visualization experiments with the micro-schlieren technique. The average diffusion coefficient and time-dependent values were measured in the PVT experiments. We also calculated the convection parameters, including Rayleigh number and critical onset time, with a series of PVT testing at the temperature ranging 293.15-423.15 K and pressure ranging 14-24 MPa by using the constant-pressure method. Through visualization experiments, we observed convective currents triggered by the density gradient in the gas-liquid interface, which noticeably enhanced the CO2 dissolution rate. The PVT testing confirmed that the diffusion coefficient increased sharply under the influence of the gravitational convection at the early stage and then decreased toward the average diffusion coefficient with time. The PVT testing also demonstrated the Rayleigh number increasing with temperature or pressure increasing under the reservoir conditions. The gravitational convection will be more likely to occur and more rapid with a greater pressure or higher temperature.

Compatibility between weak gel and microorganisms in weak gel-assisted microbial enhanced oil recovery.

To investigate weak gel-assisted microbial flooding in Block Wang Long Zhuang in the Jiangsu Oilfield, the compatibility of weak gel and microbe was evaluated using laboratory experiments. Bacillus sp. W5 was isolated from the formation water in Block Wang Long Zhuang. The rate of oil degradation reached 178 mg/day, and the rate of viscosity reduction reached 75.3%. Strain W5 could produce lipopeptide with a yield of 1254 mg/L. Emulsified crude oil was dispersed in the microbial degradation system, and the average diameter of the emulsified oil particles was 18.54 µm. Bacillus sp. W5 did not affect the rheological properties of the weak gel, and the presence of the weak gel did not significantly affect bacterial reproduction (as indicated by an unchanged microbial biomass), emulsification (surface tension is 35.56 mN/m and average oil particles size is 21.38 µm), oil degradation (162 mg/day) and oil viscosity reduction (72.7%). Core-flooding experiments indicated oil recovery of 23.6% when both weak gel and Bacillus sp. W5 were injected into the system, 14.76% when only the weak gel was injected, and 9.78% with strain W5 was injected without the weak gel. The results demonstrate good compatibility between strains W5 and the weak gel and highlight the application potential of weak gel-assisted microbial flooding.

Removal Capacities of Polycyclic Aromatic Hydrocarbons (PAHs) by a Newly Isolated Strain from Oilfield Produced Water.

The polycyclic aromatic hydrocarbon (PAH)-degrading strain Q8 was isolated from oilfield produced water. According to the analysis of a biochemical test, 16S rRNA gene, house-keeping genes and DNA-DNA hybridization, strain Q8 was assigned to a novel species of the genus Gordonia. The strain could not only grow in mineral salt medium (MM) and utilize naphthalene and pyrene as its sole carbon source, but also degraded mixed naphthalene, phenanthrene, anthracene and pyrene. The degradation ratio of these four PAHs reached 100%, 95.4%, 73.8% and 53.4% respectively after being degraded by Q8 for seven days. A comparative experiment found that the PAHs degradation efficiency of Q8 is higher than that of Gordonia alkaliphila and Gordonia paraffinivorans, which have the capacities to remove PAHs. Fourier transform infrared spectra, saturate, aromatic, resin and asphaltene (SARA) and gas chromatography-mass spectrometry (GC-MS) analysis of crude oil degraded by Q8 were also studied. The results showed that Q8 could utilize n-alkanes and PAHs in crude oil. The relative proportions of the naphthalene series, phenanthrene series, thiophene series, fluorene series, chrysene series, C21-triaromatic steroid, pyrene, and benz(a)pyrene were reduced after being degraded by Q8. Gordonia sp. nov. Q8 had the capacity to remediate water and soil environments contaminated by PAHs or crude oil, and provided a feasible way for the bioremediation of PAHs and oil pollution.

Measurement and Visualization of Tight Rock Exposed to CO2 Using NMR Relaxometry and MRI.

Understanding mechanisms of oil mobilization of tight matrix during CO2 injection is crucial for CO2 enhanced oil recovery (EOR) and sequestration engineering design. In this study exposure behavior between CO2 and tight rock of the Ordos Basin has been studied experimentally by using nuclear magnetic resonance transverse relaxation time (NMR T2) spectrum and magnetic resonance imaging (MRI) under the reservoir pressure and temperature. Quantitative analysis of recovery at the pore scale and visualization of oil mobilization are achieved. Effects of CO2 injection, exposure times and pressure on recovery performance have been investigated. The experimental results indicate that oil in all pores can be gradually mobilized to the surface of rock by CO2 injection. Oil mobilization in tight rock is time-consuming while oil on the surface of tight rock can be mobilized easily. CO2 injection can effectively mobilize oil in all pores of tight rock, especially big size pores. This understanding of process of matrix exposed to CO2 could support the CO2 EOR in tight reservoirs.