Viscosity Of Heavy Oil Research Articles

In-situ heavy oil upgrading by high temperature oxidation through air injection

Air injection has been widely considered as a technology to enhanced heavy oil recovery on account of the heavy oil upgrading caused by high temperature oxidation during this process. This paper aims at exploring the effects of oxidation thermal processing in a porous media at high temperature from 500 to 540℃ which is the high temperature oxidation range of heavy oil known from TG results, and reaction time from 8 to 16 hours for heavy oil upgrading. It was suggested that the viscosity decreased with the temperature and retention time increased due to getting less ring structure seen from IR Spectrum results. It was observed that the viscosity of heavy oil was reduced 1 to 2 orders of magnitude. Besides, the kinetics of heavy oil upgrading were analysed using five pseudo components including HO (C35+), MO (C15 ~ C35), LO (C5 ~ C14), coke, G (gas products) and successfully predicted the products results with an error of 4.34%, and great correlation to Arrhenius equation. The activation energies obtained are in the range of 44 ~ 215 kJ/mol. This work has great value in revealing the mechanisms of high temperature oxidation heavy oil upgrading and assisting heavy oil production.

Wave technologies for intensifying oil and gas extraction for fields at a late stage of development

One of the promising areas of research in the field of increasing oil recovery from reservoirs is the study of the influence of elastic vibrations on the productive reservoir. Research on the influence of elastic vibrations on stagnant oil zones in an oil reservoir in order to increase the oil recovery factor is at an early stage. The purpose of this work is to evaluate the effectiveness of using one of the wave methods to increase oil recovery. theoretical and experimental studies of the influence of elastic vibrations on changes in the parameters of the bottomhole zones of the formation and, as a consequence, increasing the productivity of oil wells and the oil recovery factor in oil fields. The work will analyze the wave method of influencing reservoir systems, such as acoustic, and evaluate the effectiveness of this method on changing the characteristics of the reservoir system. The work will conduct various studies on the practical application of wave methods. The effect of the wave method on the components and viscosity of heavy crude oil will also be studied. The proposed wave action creates the opportunity to exploit fields at later stages of development, which are characterized by a high content of asphaltenes, resins and paraffins. The results of the wave impact confirmed the effectiveness of this technology, which made it possible to double the turnaround time.

Reducing the viscosity of missan heavy crude oil using combinations of low molecular weight hydrocarbon compounds

This work studied the facilitation of the transportation of Missan heavy crude oil characterized with high viscosity 84.61 cp at 15 °C, low API 23.1, by reducing its viscosity from break down asphaltene agglomerates using five solvents with some novel combinations of chemical additives were used for this study (naphtha & toluene, naphtha & xylene, naphtha & kerosene, toluene & kerosene, and xylene & kerosene).The viscosity of crude oil was measured after being treated with these chemicals at different concentrations (4, 8, and 12 weight%) and temperatures 15, 25, 35, and 45 °C. It has been found that increasing the concentration of naphtha with xylene from 4% to 12% causes a decrease in viscosity, from 48.62 cp at 15°C to 30.11 cp. The viscosity of a mixture of naphtha and kerosene drops from 50.15 cp at 15°C to 31.70 cp when the concentration is raised from 4% to 12%. The addition of toluene to kerosene causes the viscosity to drop from 51.76 cp at 15°C to 33.67 cp when the concentration of toluene is raised from 4% to 12%. Increasing the xylene concentration from 4% to 12% in kerosene led to a decrease in viscosity from 53.65 cp at 15°C to 34.88 cp at the same temperature. The findings of the present work could be applied to the petroleum industry for the purpose of transporting heavy oil of Missan or any other heavy crude.

Influence and Mechanism Study of Ultrasonic Electric Power Input on Heavy Oil Viscosity

The reserves of heavy oil are enormous. However, its high viscosity and other characteristics make heavy oil extraction and transportation extremely difficult. Power ultrasonic (US) reforming technology on heavy oil has the advantages of environmental protection and fast results, so it is important to understand the mechanism of ultrasonic reforming. We examine the influence law of the electric power input of the US transducer on the viscosity of heavy oil. Fourier Transform Infrared Spectrometer (FTIR) and Gas Chromatography (GC) are applied to explain the changes in different functional groups, heavy components, and carbon chains before and after US irradiation. The cavitation noise method is also used to study the influences of variance in the intensity of cavitation on the viscosity of heavy oil. The results indicate that the viscosity of heavy oil first decreases, and next increases with an increase in electric power. The functional groups and chromatographic distillation also change in different forms, and with an increase in electric power, the cavitation effect is gradually enhanced. These findings suggest that it is not that the stronger the cavitation, the greater the influence on the viscosity of heavy oil.

The effect of chlorella hydrothermal products on the heavy oil upgrading process

In-situ upgrading can improve the scale of heavy oil development, but the efficiency of in-situ hydrothermal hydrogen supply is limited. In this paper, the combination of algae hydrothermal liquefaction and heavy oil upgrading and viscosity reduction process is proposed. The liquefaction products of hydrothermal liquefaction are used to supply hydrogen to the heavy oil upgrading and viscosity reduction process, thereby enriching the supply path of active hydrogen. The effects of hydrothermal liquefaction temperature of Chlorella and the addition of 5% Fe/HZSM-5 catalyst on the liquefaction rate and product distribution of Chlorella were investigated, and the upgrading and viscosity reduction process of heavy oil with the participation of hydrothermal liquefaction products was discussed. The results show that when the temperature of upgraded heavy oil is 280 °C and 5 wt% of hydrothermal liquefaction products are added and reacted for 24 h can make the viscosity reduction rate of heavy oil reach 84.32%, and 31.2% of resin in heavy oil was converted into aromatic hydrocarbon. Elemental analysis showed that the upgraded heavy oil H/C ratio increased, and GC–MS analysis showed that the distribution of algae hydrothermal liquefaction products could be adjusted by the catalyst, and more aromatics were produced after the addition of the catalyst, which confirmed that the aromatics in hydrothermal liquefaction products had a significant effect on the quality improvement and viscosity reduction of heavy oil. Its molecular weight was also found to be reduced from 853 to 326 in the average molecular weight test (GPC). The efficient carbon sequestration of algae is combined with the demand for carbon dioxide emission reduction in oilfields to realize the recycling of carbon resources.

Multi-round CO2 Viscosity-reducing Oil Production Technology without Pulling out Downhole Pipe Column

Carbon dioxide injection can improve the recovery rate of heavy oil and reduce the viscosity of heavy oil as well as reduce carbon emissions. However the downhole tubular material is very easy to react electrochemically with CO2 under high temperature and humid environment after CO2 injection, which causes strong corrosion to the downhole tubulars. For directional wells, it will further aggravate the tubular bias wear and cause a significant shortening of the pumping inspection cycle. Moreover production will decrease after a period of time CO2 throughput and re-injection of CO2 will be required. In this paper, we have developed a multi-round carbon injection and heavy oil production technology without moving the tubing column. Also the supporting tools match the technology is optimized and improved to achieve the goal of extending the operation cycle and saving cost.

A Critical Review Using CO2 and N2 of Enhanced Heavy-Oil-Recovery Technologies in China

Thermal recovery technology is generally suitable for shallow lays due to the higher thermal loss for the deep heavy-oil reservoirs. Non-thermal recovery technologies, such as the non-condensate gas injection technology, are not limited by the reservoir depth and could be extensively applied for the heavy-oil reservoir. Many experimental studies and field applications of non-condensate gas injection have been conducted in heavy-oil reservoirs. The injected non-condensate gas could achieve dynamic miscibility with heavy oil through multiple contacts, which has a significant viscosity-reduction effect under the reservoir conditions. In addition, the equipment involved in the gas injection operation is simple. There are many kinds of non-condensate gases, and common types of gases include N2 and CO2 due to abundant gas sources and lower prices. Moreover, CO2 is a greenhouse gas and the injection of CO2 into the reservoir would have environmental benefits. The non-thermodynamic method is to inject N2 and CO2 separately to produce heavy oil based on the mechanism of the volume expansion of crude oil to form elastic flooding and reduce crude oil viscosity and foamy oil flow. Steam injection recovery of the thermodynamics method has the disadvantages of large wellbore heat loss and inter-well steam channeling. The addition of N2, CO2, and other non-condensate gases to the steam could greatly improve the thermophysical properties of the injected fluid, and lead to higher expansion performance. After being injected into the reservoir, the viscosity of heavy oil could be effectively reduced, the seepage characteristics of heavy oil would be improved, and the reservoir development effect could be improved. Non-condensate gas injection stimulation technology can not only effectively improve oil recovery, but also help to achieve carbon neutrality, which has a very broad application prospect in the future oil recovery, energy utilization, environmental improvement, and other aspects.

Effect of ammonium based ionic liquids on the rheological behavior of the heavy crude oil for high pressure and high temperature conditions

Heavy crude oil (HCO) production, processing, and transportation forms several practical challenges to the oil and gas industry, due to its higher viscosity. Understanding the shear rheology of this HCO is highly important to tackle production and flow assurance. The environmental and economic viability of the conventional methods (thermal or dilution with organic solvents), force the industry to find an alternative. The present study was constructed to investigate the effect of eco-friendly ionic liquids (ILs) on the HCO's rheology, at high temperature and high pressure. Eight different alkyl ammonium ILs were screened for HCO's shear rheology at the temperatures of 25–100 °C and for pressures 0.1–10 MPa. The addition of ILs reduced the HCO's viscosity substantially from 25 to 33% from their original HCO viscosity. Also, it aids to reduce the yield stress to about 15–20% at all the studied experimental conditions. Furthermore, the viscoelastic property of the HCO was studied for both strain-sweep and frequency-sweep and noticed the ILs helps to increase HCO's loss modulus (G″) by reducing storage modulus (G′), it leads to the reduction of the crossover point around 25–32% than the standard HCO. Mean the ILs addition with HCO converts its solid-like nature into liquid-like material. Besides, the effect ILs chain length was also studied and found the ILs which has lengthier chain length shows better efficiency on the flow-ability. Finally, the microscopic investigation of the HCO sample was analyzed with and without ILs and witnessed that these ILs help to fragment the flocculated HCO into smaller fractions. These findings indicate that the ILs could be considered as the better alternative for efficient oil production, processing, and transportation. • Aliphatic ionic liquids reduce the viscosity of heavy oil significantly. • Ionic liquid with [HSO 4 ] - or [H 2 PO 4 ] - anion shows better efficiency. • Ionic liquids addition with heavy oil converts its solid-like nature into liquid-like material. • Ionic liquids helps fragment the flocculated heavy oil into a smaller fraction. • Greater the chain length of ionic liquid, higher is the tendency on improving flow-ability.

Experimental Study on Chemical Recovery of Low-Permeability and Medium-Deep Heavy Oil Reservoir

To improve the oil recovery of a block in the Wutonggou Formation of the Changji Oilfield, viscosity reducing and foaming agent was optimized to improve the development effect of the water flooding reservoir. The core flooding experiment and microscopic visual experiment were conducted to investigate the production characteristics and EOR mechanism of nitrogen foam flooding. The results show that the 0.5 wt% viscosity reducing and foaming agent DXY-03 was optimized. In the process of microscopic oil displacement by nitrogen foam, nitrogen foam continuously expands and spreads, improves oil displacement efficiency, and greatly improves oil recovery through emulsification and viscosity reduction, squeezing action, dragging action, and Jamin effect. The core flooding experiment shows that on the basis of the water flooding recovery rate of 20.3%, the nitrogen foam huff and puff is increased by 9.2%. The viscosity reducing and foaming agent flooding is increased by 7.8%, and the nitrogen foam flooding is increased by 12.9%. The main EOR mechanism of the viscosity reducing and foaming agent is that it can reduce the interfacial tension between oil and water and can promote heavy oil emulsification and dispersion, thereby forming an oil/water- (O/W-) type emulsion. The reduction in the viscosity of heavy oil makes crude oil easier to extract, realizing the synergistic viscosity reducing and efficiency enhancing effect of nitrogen and viscosity reducing and foaming agents. This study is helpful to provide reference for the development of low-permeability and high-viscosity medium-deep heavy oil reservoirs by chemical agents combined with cold production.

Measurements of the Density and Viscosity of Heavy Oil and Water-in-Oil Emulsions Over a Wide Temperature Range

Density and dynamic viscosity of extra viscous heavy crude oil and water-in-oil (W/O) suspensions based on Ashalchinskaya (Tatarstan, Russian Federation) oil have been measured as a function of temperature and concentration of water at atmospheric pressure. The measurements were made at temperatures from (293 to 463) for density and from (293 to 367) K for viscosity with various concentrations of water (from 0 % to 30 % volume fraction). Measurements were made using modified hydrostatic weighing for density and falling body techniques for viscosity. The combined expanded uncertainty of the density, viscosity, pressure, and temperature measurements at 0.95 confidence level with a coverage factor of k = 2 is estimated to be $$U\left( \rho \right)$$ = 0.16 % and $$U\left( \eta \right)$$ = 1.0 %, $$U\left( P \right)$$ = 1.0 %, and $$U\left( T \right)$$ = 0.02 K, respectively. The reliability and accuracy of the new experimental method and correct operation of the modified experimental apparatus was confirmed with measurements using different methods (pycnometric, capillary flow, commercial standard instruments, Brookfield rotational viscometer). The effect of temperature and concentration of water on the measured values of density and viscosity of W/O suspensions were studied. Using crude dry oil, the effective viscosities of several synthetic W/O emulsions are measured at atmospheric pressure using a commercial standard instrument, Brookfield rotational viscometer and falling body technique for different shear rates, temperatures and volume fractions of the dispersed phase. The various correlation equations for describing viscosity as a function of temperature and dispersed phase volume fraction is developed. A number of factors such as water content, shear rate, shear stress, and temperature and their effects on the density and dynamic viscosity of dry crude oil and W/O emulsions were assessed.

Ionic liquids enhanced oil recovery from oily sludge-experiment and mechanism

The oily sludge would cause environment pollution, and would cause the heavy oil waste. Therefore, it was vital for us to find novel methods to obtain heavy oil from the oily sludges. In this study, the [C12mim][PF6] and [C12mim][Br] ionic liquids(ILs) were used to enhance the oil recovery. The toluene could obtain the highest oil recovery, and both the two ILs could increase the oil recovery. Toluene could obtain the highest oil recovery (89.4 wt%), and n-octane could obtain the lowest oil recovery (76.8 wt%). [C12mim] [PF6] could efficiently increase the heavy oil recovery to 91.2 wt%(by toluene). The [C12mim][Br] could increase the heavy oil recovery further. Both the [C12mim] [PF6] and the [C12mim][Br] ionic liquids could increase the heavy ois C/H ratio, decrease heavy oil viscosity and increase the sands hydrophilicity. The [C12mim][Br] ionic liquids showed better effect. In addition, the ionic liquids could increase the solvents recovery, and the ionic liquids recovery were high. Therefore, the ionic liquids enhanced oil recovery could be recycled to ten times. The two ionic liquids could effectively decrease the heavy oil interaction force, and when the ionic liquids increased to 200 ppm, the force remained stable. In the end, the ionic liquids enhancing solvent extraction mechanism was put forward.

Determination of the concentration-dependent effective diffusivity of CO2 in unconsolidated porous media saturated with heavy oil by considering the swelling effect

Effective diffusivity of CO2 in the unconsolidated sandpack saturated with a Lloydminster heavy oil was determined in the form of an exponential function of CO2 concentration in the diluted and swollen liquid-phase. For such a purpose, two pressure-decay experiments were executed at different pressure ranges (i.e., 855–817 kPa and 1993–1905 kPa) and a temperature of 299.65 K. First, the sandpack saturated with heavy oil was prepared under an increased temperature of 348.15 K because the reduced heavy oil viscosity was required to saturate the sand column with heavy oil in a diffusion cell. Next, the diffusion cell containing the Lloydminster heavy oil-saturated sand column was integrated into a pressure-decay experimental system with pressure-monitoring devices. Then, pressure-history curves of both the diffusion experiments were continuously recorded to be compared with the theoretically calculated ones. The Fick's 2nd law incorporated with the volume-translated Peng-Robinson equation of state (PR-EOS) was implemented to determine the concentration-dependent effective diffusivity of CO2 in a sandpack saturated with heavy oil considering its swelling effect through minimizing the deviations between the theoretically computed pressure-history curves with the experimentally recorded ones. For the computation of the Fick's 2nd law, the Crank-Nicolson scheme finite difference method (FDM) was applied to take the local oil swelling into account for enhancing the accuracy of such a determined diffusivity. The excellent agreements between the theoretically computed and experimentally measured pressure-history curves at both the pressure ranges signify that such a determined effective diffusivity considering the CO2 concentration is accurate and reliable.

Insights into the Structure-Performance Relationship and Viscosity Reduction Performance of Recyclable Magnetic Fe/Zeolite for Crude Oil Aquathermolysis.

Elucidating the structure-performance relationship of zeolites and their synergy with metals for the catalytic aquathermolysis of crude oil is crucial for designing efficient catalysts. Herein, the structure-performance relationship between the magnetic Fe-loaded zeolite's physicochemical properties and aquathermolysis performance is mainly explored. First, the catalytic aquathermolysis performance of various porous materials (Y, β, MCM-41, and ZSM-5 zeolites) was probed to investigate the effect of different topological structures on the viscosity reduction of heavy oil. Results showed that ZSM-5 has a favorable pore structure and acidity, and its viscosity reduction performance is 1.7-4.1 times those of other zeolites; therefore, it is more suitable as a carrier for aquathermolysis to reduce viscosity. Then, Fe substance (such as Fe2O3 and Fe3O4) was loaded onto the ZSM-5 support. It was found that Fe3O4/ZSM-5 had better performance compared with pure ZSM-5 and Fe2O3/ZSM-5, which could reduce the viscosity of heavy oil by 20.3%. Importantly, the Fe3O4/ZSM-5 catalyst is easily separated from crude oil due to its magnetism, hence it has the potential to be recycled and reused. In addition, the potential structure-performance relationship was systematically studied by X-ray diffraction (XRD), elemental analysis (EL), transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FT-IR). As a result, it was considered that Fe3O4/ZSM-5 broke C-S bonds and reduced the heavy components (resin and asphaltene) of crude oil. This study has a certain guiding significance for developing heterogeneous magnetic hydrothermal viscosity reduction catalysts.

Bio‐based mixed CO2‐switchable surfactant for reducing viscosity of heavy oil

AbstractCO2‐switchable surfactants have significant viscosity‐reducing abilities, but their applicability is limited by the complexity of their manufacture. In this work, a simple mix of CO2‐switchable bio‐based surfactants N‐lauroylsarcosine (LS) and glucosamine (GA) was used to reduce viscosity of heavy crude oil. Surface tensiometer was used to investigate the surface activity of LS/GA, revealing the potential for viscosity reduction. By alternating sparging of CO2 and N2, the switchability of LS/GA was examined and proved. It reveals that LS/GA significantly reduces the viscosity of heavy oil by emulsification, but the formed emulsion can be quickly destabilized by introduction of CO2. The results of this study reveal that CO2‐switchable bio‐based surfactants with viscosity‐reducing capabilities for heavy crude oil may be produced by simple mixing, paving the way for reversible emulsification of heavy crude oil utilizing CO2‐switchable bio‐based surfactant.

Mechanism Analysis of Heavy Oil Viscosity Reduction by Ultrasound and Viscosity Reducers Based on Molecular Dynamics Simulation.

Ultrasound and viscosity reducers are commonly used methods to reduce the viscosity of heavy oil. In order to compare the viscosity reduction effects of ultrasound and viscosity reducers and study their mechanism of interaction on heavy oil, molecular dynamics simulation was carried out in this paper. First, a molecular model of heavy oil composed of asphaltene, resin, aromatic hydrocarbon, and saturated hydrocarbon was established in this work. Through molecular dynamics simulation, the different effects of ultrasound and viscosity reducers on the viscosity reduction rate, hydrogen bond number, hydrogen bond type, and occupation rate were obtained, and the viscosity reduction mechanism of ultrasound and viscosity reducers was analyzed. By calculating the viscosity reduction rate and the number of hydrogen bonds of five oil-soluble viscosity reducers with or without ultrasound, it was found that the types of hydrogen bonds affecting the viscosity reduction effect were different with or without ultrasound or viscosity reducer, and the type and content of viscosity reducer would affect the effect of ultrasonic viscosity reduction. The amplitude, frequency, and temperature of ultrasound were also the factors affecting the effect of viscosity reducers. The simulation results helped to explain the mechanism of jointly reducing the viscosity of heavy oil by ultrasound and viscosity reducers from the microscopic point of view and provided a theoretical basis for the industrial application of ultrasound and viscosity reducers to reduce the viscosity of heavy oil.

Octahedral Cluster Complex of Molybdenum as Oil-Soluble Catalyst for Improving In Situ Upgrading of Heavy Crude Oil: Synthesis and Application

Heavy oil resources are attracting considerable interest in terms of sustaining energy demand. However, the exploitation of such resources requires deeper understanding of the processes occurring during their development. Promising methods currently used for enhancing heavy oil recovery are steam injection methods, which are based on aquathermolysis of heavy oil at higher temperatures. Regardless of its efficiency in the field of in situ upgrading of heavy oil, this technique still suffers from energy consumption and inefficient heat transfer for deeper reservoirs. During this study, we have developed a molybdenum-based catalyst for improving the process of heavy oil upgrading at higher temperature in the presence of water. The obtained catalyst has been characterized by a set of physico-chemical methods and was then applied for heavy oil hydrothermal processing in a high-pressure reactor at 200, 250 and 300 °C. The comparative study between heavy oil hydrothermal upgrading in the presence and absence of the obtained molybdenum-based oil soluble catalysts has pointed toward its potential application for heavy oil in situ upgrading techniques. In other words, the used catalyst was able to reduce heavy oil viscosity by more than 63% at 300 °C. Moreover, our results have demonstrated the efficiency of a molybdenum-based catalyst in improving saturates and light hydrocarbon content in the upgraded oil compared to the same quantity of these fractions in the initial oil and in the non-catalytically upgraded oil at similar temperatures. This has been explained by the significant role played by the used catalyst in destructing asphaltenes and resins as shown by XRD, elemental analysis, and gas chromatography, which confirmed the presence of molybdenum sulfur particles in the reaction medium at higher temperatures, especially at 300 °C. These particles contributed to stimulating hydrodesulphurization, cracking and hydrogenation reactions by breaking down the C-heteroatom bonds and consequently by destructing sphaltenes and resins into smaller fractions, leading to higher mobility and quality of the upgraded oil. Our results add to the growing body of literature on the catalytic upgrading of heavy oil in the presence of transition metal particles.

Span 80 effect on the solvent extraction for heavy oil recovery

In this study, we used the Span 80 to enhance solvent extraction process, and we explored the mechanism. The results indicated different solvents would obtain different oil recovery, and toluene showed the optimal oil recovery, and the n-heptane showed the lowest oil recovery. The complex solvents could improve oil recovery. Toluene could make the heavy oil show the lowest viscosity (89.6 Pa.S), and n-heptane make the heavy oil show the highest viscosity (176.3 Pa.S). Complex solvents could decrease the heavy oil viscosities. The higher C/H was, the higher heavy oil recovery was, and when the asphaltene and resins content increase, the C/H would increase. The C/H showed the highest value (9.09, by toluene) and the lowest value (8.15). In this study, Span 80 could increase heavy oil C/H ratio, decrease heavy oil viscosity. Span 80 could make the sands surface more hydrophilic, and then the solvent loss would decrease. The oil recovery was high after 10 times recycle use.

Insights into enhanced oil recovery by thermochemical fluid flooding for ultra-heavy reservoirs: An experimental study

The thermal recovery method (especially for steam injection) is widely used for heavy oil recovery due to the high viscosity and poor fluidity of heavy oil. In this paper, a thermochemical fluid flooding is proposed for ultra-heavy oil reservoirs. The different thermochemical fluid flooding methods are compared, and the best flooding method is suggested. The synergistic effect of thermochemical fluid on oil viscosity is investigated, and the injection parameter optimization is selected. Finally, the feasibility of multi-stage viscosity reduction is discussed, and a suitable experimental scheme is also proposed. The results show that DCS (viscosity reducer (D) + CO2 (C) + steam (S)) flooding exhibits the highest oil recovery (about 70.3 %). The thermal viscosity reduction by steam decreases the oil viscosity, which is helpful for CO2 and viscosity reducer diffusion. Besides, the enhanced CO2 diffusion can also reduce oil viscosity and facilitate viscosity reducer diffusion. Therefore, viscosity reducer, CO2, and steam have a synergistic effect on oil viscosity reduction. The average oil recovery increases rapidly with the CO2 volume and then slows down, which is similar to that of viscosity reducer. The inflection points for CO2 and viscosity reducer appear at 0.20 PV (pore volume) and a concentration of 2.0 %, respectively. The optimal injection parameters for DCS flooding are 2.0 % of viscosity reducer + 0.20 PV CO2 + 2.5 PV steam. The multi-stage viscosity reduction is feasible for thermochemical fluid flooding due to the prolonged effective action time of the viscosity reducer. The CO2 multiple stages injection has less impact on the oil recovery (a difference of 1.08 %). The DCSDS (viscosity reducer + CO2 + steam + viscosity reducer + steam) flooding is recommended from the perspective of cost reduction.

Laboratory Experiments on the In Situ Upgrading of Heavy Crude Oil Using Catalytic Aquathermolysis by Acidic Ionic Liquid.

Heavy and extra heavy oil exploitation has attracted attention in the last few years because of the decline in the production of conventional crude oil. The high viscosity of heavy crude oil is the main challenge that obstructs its extraction. Consequently, catalytic aquathermolysis may be an effective solution to upgrade heavy crude oil to decrease its viscosity in reservoir conditions. In this regard, a series of acidic ionic liquids, 1-butyl-1H-imidazol-3-ium 4-dodecylbenzenesulfonate (IL-4), 1-decyl-1H-imidazol-3-ium 4-dodecylbenzenesulfonate (IL-10), and 1-hexadecyl-1H-imidazol-3-ium 4-dodecylbenzenesulfonate (IL-16), were utilized in the aquathermolysis of heavy crude oil. Of each IL, 0.09 wt % reduced the viscosity of the crude oil by 89%, 93.7%, and 94.3%, respectively, after the addition of 30% water at 175 °C. ILs with alkyl chains equal to 10 carbon atoms or more displayed greater activity in viscosity reduction than that of ILs with alkyl chains lower than 10 carbon atoms. The molecular weight and asphaltene content of the crude oil were decreased after catalytic aquathermolysis. The compositional analysis of the crude oil before and after catalytic aquathermolysis showed that the molar percentage of lighter molecules from tridecanes to isosanes was increased by 26–45%, while heavier molecules such as heptatriacontanes, octatriacontanes, nonatriacontanes, and tetracontanes disappeared. The rheological behavior of the crude oil before and after the catalytic aquathermolytic process was studied, and the viscosity of the crude oil sample was reduced strongly from 678, 29.7, and 23.4 cp to 71.8, 16.9, and 2.7 cp at 25, 50, and 75 °C, respectively. The used ILs upgraded the heavy crude oil at a relatively low temperature.

Three-dimensional network gel structure and viscosity reduction mechanism of heavy oil

The internal structure of heavy oil plays an important role in the research of the viscosity reduction mechanism of heavy oil. On the one hand, the influence of heavy oil composition on the viscosity of heavy oil is discussed. The results show that the influence rate of composition on viscosity is Asphaltenes (0.11377) > resins (0.07566) > saturated hydrocarbon (−0.06027) > aromatics (−0.07536), and the influence range of composition on viscosity is Asphaltenes (3.5348%) > resins (2.828%) > saturated hydrocarbon (0.861%) > aromatics (0.167%). On the other hand, the structural changes of heavy oil before and after viscosity reduction were studied by elemental analysis, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and scanning electron microscopy (SEM). Based on Yen's heavy oil colloid model, the hypothesis of the three-dimensional network gel structure model is put forward. The possible reason for forming the gel structure is that the system contains a large number of gel factors, which can spontaneously aggregate and assemble into ordered structures in the solvent. What's more, the hypothesis of heavy oil gel structure was verified by rheological experiments. Rheological tests showed that resins and Asphaltenes were packed together by hydrogen bonds and π-π bonds, forming a tight gel network structure. Saturates and aromatics were dispersed in heavy oil as solvents. The essence of heavy oil viscosity reduction is that the π-π bonds and hydrogen bonds are destroyed, disintegrating the heavy oil gel structure, which is transformed into a sol structure model.