Viscosity Reduction Effect Research Articles

Co-Gelatinization Modification of Iodine–Starch and Its Performance in Drilling Fluid

Modified starch is used as a drilling fluid treatment agent in oilfields. During the drilling process, modified starch plays a vital role in the drilling fluid system, but its poor temperature resistance limits its application in oilfields. Therefore, this paper studied the performance of several starches in water-based drilling fluids through co-gelatinization modification; studied the effectiveness of several modifiers in gelatinized starch drilling fluids, combined with flow modification performance tests, bentonite linear expansion rate, salt resistance, and other experimental methods to complete the screening of the best modified starch; and systematically compared the temperature resistance, inhibition, compatibility, and salt resistance before and after gelatinization. The possible mechanism of action of modified starch treatment was analyzed and tested by Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), laser particle size analyzer and scanning electron microscopy (SEM). The results showed that the decomposition temperatures of cassava starch (TS), potato starch (PS), and corn starch (CS) were different, and the decomposition temperature of cassava starch (TS) was the highest, at 150 °C. At this temperature, the optimal dosage of gelatinized TS is 2.5%, the maximum shear force is 2.25 Pa, and the filtration loss is only 12.6 mL. TS has obvious performance advantages over other starches. After co-gelatinization with 1.0% iodine and 2.5% TS at 140 °C, it has a good viscosity reduction and filtration loss effect, and the filtration loss is only 5.2 mL, which is 31.6% lower than that of untreated TS drilling fluid. The linear expansion rate at 120 min is 10.85%, indicating that it has a strong inhibitory effect on the hydration and dispersion of bentonite. In addition, iodine cassava starch (ITS) has good compatibility in drilling-fluid formulations and shows good salt resistance when mixed with different concentrations of KCl. The results of this study can be used to improve the temperature resistance of filtration agents and facilitate related research.

Thermosensitive polymer/nanosilica hybrid as a multifunctional additive in water-based drilling fluid: Rheologicalproperties and lubrication performance as well as filtration loss reduction capacity

In previous studies, for obtaining a flat rheological drilling fluid, binary and ternary thermosensitive silica (SiO2) nanohybrids as rheological modifiers were synthesized using N-isopropylacrylamide with a thermal association temperatureof 32–33 °C as the thermosensitive monomer [J. Petrol. Sci. Eng. 219 (2022), 111096; Geoenergy Science and Engineering 228 (2023), 211934]. However, the as-synthesized SiO2 nanohybrids exhibited limited performance and low thermal transition temperature. Thus surface initiated atom transfer radical polymerization was utilized to graft hydrophilic poly(ethylene glycol) methyl ether methacrylate (PEGMA) onto SiO2 surface to obtain PEGMA/SiO2 nanohybrids with an elevated thermal association temperature of 75 °C. The morphology and structure of the as-synthesized PEGMA/SiO2nanohybrid were characterized by infrared spectroscopy and transmission electron microscopy; and its effects as a thermosensitive multifunctional additive on the rheological properties and lubrication performance as well as filtration loss reduction capacity of a water-based drilling fluid were investigated. Results indicate that the drilling fluids with 1.0% PEGMA/SiO2 nanohybrids exhibited obvious thermal thickening behavior in the temperature range of 70–80 °C; at low temperatures, however, they had a significant viscosity reduction effect therein. At room temperature, the apparent viscosity and plastic viscosity were reduced by 68% and 50%, respectively. Besides, due to the tightly packed plugging layer formed by PEGMA/SiO2 nanohybrids and bentonite, the filtration loss of the drilling fluids containing 1.0% PEGMA/SiO2 nanohybrid was reduced by 37% as compared with that of the base slurry; and the lubrication coefficient was decreased by up to 50%. Moreover, the high-temperature aging process promoted the intermolecular interactions of the nanohybrids and their interaction with bentonite flakes, thereby further improving the rheological behavior, filtration reduction ability, and lubricity of the drilling fluids. The as-synthesized thermosensitive PEGMA/SiO2 nanohybrids with excellent multifunctionality could find promising application in water-based drilling fluids.

Effects of wall heating on wall pressure fluctuations and flow noise in a low-Reynolds-number turbulent channel flow with temperature-dependent viscosity

Wall pressure fluctuations and flow noise substantially degrade sonar detection performance and the acoustic stealth performance of underwater vehicles. This paper numerically investigates the effects of wall heating on wall pressure fluctuations in turbulent channel flow of water with temperature-dependent viscosity, exploring a novel method for controlling wall pressure fluctuations and flow noise in underwater vehicles. Large-eddy simulation (LES) is employed for the numerical calculation of the flow field, while a hybrid method combining LES with Lighthills acoustic analogy is employed to predict flow noise. The numerical results show that when the temperature difference between the wall and the incoming flow is 30 K and 50 K, the peak root-mean-square pressure fluctuations decrease by 6.76% and 8.91%, respectively. Wall heating stabilizes the pressure field near the wall, with the spectral levels of wall pressure fluctuations showing average decreases of approximately 1 dB and 2 dB. Wall heating weakens the energy-containing structures of wall pressure fluctuations and increases the overall convection velocity by 1.22% and 3.81%, respectively. Flow structure analysis reveals that the weakening of energy-containing structures results from the suppression of the vortex structures in the near-wall region. In the wall heating cases, peak turbulent kinetic energy decreases by 12.6% and 15.8%, respectively. Moreover, the sound pressure level of flow noise decreases with increasing wall temperature, with the maximum noise reduction exceeding 3 dB. Previous studies have not yet explored the effects of viscosity reduction caused by wall heating on wall pressure fluctuations and flow noise. This study demonstrates that wall heating is a promising method for reducing wall pressure fluctuations and flow noise.

Study on Mechanism and Effect of Different Viscosity Reducing Methods on Offshore Heavy Oil

Abstract Bohai is rich in heavy oil. And its efficient development is significant. In this essay, ordinary heavy oil and extra one were selected, and the viscosity characteristics was also investigated referring to its internal composition. And so as the reducing viscosity effects of steam, oil-soluble viscosity reducer, diesel, emulsifier, flue gas and carbon dioxide. The experimental results show that resin and asphaltene content have positive effect on the viscosity of heavy oil. Compared with ordinary heavy oil, the drop is significantly greater when the temperature increases by 10°C. For ordinary heavy oil, the inflection point temperature is from 50°C to 70°C, and for extra-heavy oil, it is above 100°C. For ordinary heavy oil, its flow effect can be better improved without too high temperature, while it’s totally different for super heavy oil. For which, higher temperature and other auxiliary viscosity reduction methods are needed to achieve better flow performance. Diesel oil reduce viscosity of heavy oil by similar solubility principle, but the demand for diesel oil is large. At 50°C, the viscosity of super heavy oil with 0.5% emulsion viscosity reducer added is 36 mPa·s, but the water content needs to reach above 30%.Oil-soluble viscosity reducer reduces viscosity by dissolving asphaltenes and resins and dismantling aggregate structure of heavy oil aromatic flakes.However, the dosage should reach about 20 %, so that the viscosity of super heavy oil can be reduced to the level of dilute oil. Overall, for developing super heavy oil, steam compound with oil soluble viscosity reducer can be taken into account at the early production stage, and the emulsion viscosity reducer can be used in the middle development stage and wellbore viscosity reduction and lifting process. Finally, for ordinary heavy oil, flue gas’s viscosity reduction effects, nitrogen and carbon dioxide are investigated. It is found that the viscosity reduction effect of carbon dioxide is the best, followed by flue gas and nitrogen. Considering the offshore gas source, cost and carbon emission requirements, it is recommended to use flue gas in the field. The research provides theoretical guidance and technical reference for development of different types of offshore heavy oil.

Mathematical modeling for the production performance of cyclic multi-thermal fluid stimulation process in layered heavy oil reservoirs

Multi-thermal fluid (MTF), with a unique thermophysical characteristics, has been widely applied in the enhanced heavy oil recovery processes. Especially for the layered heavy oil reservoirs, MTF shows more attractive than the conventional saturated steam. In this study, we propose an improved mathematical model for the production performance of cyclic MTF stimulation process in layered heavy oil reservoirs. In this model, based on a three-zone assumption, we first derive a productivity model for the thermal-fluids huff-n-puff process in layered heavy oil reservoirs. Thereafter, considering the typical EOR mechanisms of non-condensable gases in MTF, the viscosity reduction effect caused by CO2 dissolution and the effect of formation energy supplement caused by N2 are mathematically described. Simultaneously, because of the nonlinear temperature spreading behavior in the formation, an MTFs flooding experiment is also performed to characterize the effect. Meanwhile, a heating radius model with the consideration of steam overlap effect is also involved in our model. Then, the calculation results are compared against the results of a commercial simulator to confirm the accuracy, while a sensitivity analysis on the reservoir and operation parameters is performed. This paper provides a quick estimation approach for the productivity of cyclic MTF stimulation process in layered heavy oil reservoirs.

The Influencing Factors and Mechanism of Anionic and Zwitterionic Surfactant on Viscosity Reduction in Heavy O/W Emulsions.

The high viscosity of heavy crude oil has been an obstacle to its safe production and economic transportation. In this work, a screened emulsified viscosity reducer system is conducted. Experimental results demonstrate that the most effective viscosity reducing agent comprises sodium oleate (NaOl) and cocamidopropyl betaine (CAB-35) in a ratio of 1:2, achieving a viscosity reduction rate of 94.65%. Additionally, the interfacial tension between oil and water decreases from 27 to 4 mN/m with 0.1 mass % TEOA and NaOH in a 1:1 ratio. The oil droplet size is uniformly distributed with D mean is 14 μm and D 50 is 11 μm. Droplets flocculate as the salinity increases to 0.2 mol/L, which corresponds to the apparent increase of viscosity. The adsorption of long alkyl chain lipophilic groups on surfactant molecules at the oil-water interface and the water film alters the wettability of pipe steel to water-wet, further enhancing the application of emulsification and viscosity reduction effects. The primary mechanism behind the viscosity reduction in emulsification is attributed to strong electrostatic interactions stemming from molecular electrostatic potential distributions.

High-Efficiency High-Temperature-Resistant Nanosilica Viscosity Reducer for Extra-Heavy Oil Viscosity Reduction.

Due to the fact that more conventional heavy oil recovery methods (heating, emulsification, dilution, and other methods) have many shortcomings, they cannot meet the demand of heavy oil exploitation. Therefore, there is a need for new recovery methods. In this paper, the surface of nano SiO2 was modified with a silane coupling agent, KH-560, to prepare a nanoviscosity reducer (NRV), which has high-temperature resistance (300 °C), calcium and magnesium resistance (Ca2+ + Mg2+ > 900 mg/L) and high viscosity reduction rate (>99%). FTIR and SEM measurements showed that KH560 has been successfully connected to the surface of SiO2. The particle size distribution of NRV is mainly distributed in 50-80 nm, which matches the results of SEM. The experimental results showed that the viscosity reduction rates of 1 wt % NRV on M-1 heavy oil before and after aging were 99.73% and 99.71%, respectively. The viscosity reduction effect of 1% NRV on M-1 heavy oil and the bleeding rate of emulsion formation were investigated when the oil-water ratio ranged from 9:1 to 1:9. The results showed that when the oil-water ratio was between 7:3 and 1:9, the viscosity reduction rate was greater than 99%. Besides, the bleeding rate of emulsion increases with the decrease of the oil-water ratio. What's more, static and dynamic adsorption experiments showed that the adsorption capacity of 1 wt % NRV was 1.746 mg/g and 1.668 mg/g sand, respectively. The interfacial tension experiment showed that the interfacial tension (IFT) between 1 wt % NRV and M-1 heavy oil was 0.052 mN/m, and low interfacial tension was beneficial to displace the oil in the formation pores. At the same time, the displacement effect of NRV on M-1 heavy oil at different concentrations (0.5, 1.0, and 1.5 wt %) and temperatures (200, 250, and 300 °C) was investigated by core flooding experiments. The results showed that the recovery rate increases with the increase of NRV concentration, and 1 wt % NRV at 300 °C will improve the recovery rate of M-1 heavy oil by 27.3% compared to steam flooding. NRV could reduce the viscosity of crude oil, which provides technical guidelines for the exploitation of heavy oil and extra heavy oil.

Research on the quantitative relationship of the viscosity reduction effect of large-ring cyclodextrin on potato starch during gelatinization process and mechanism analysis

Starch is extensively used across various fields due to its renewable properties and cost-effectiveness. Nonetheless, the high viscosity that arises from gelatinization poses challenges in the industrial usage of starch at high concentrations. Thus, it's crucial to explore techniques to lower the viscosity during gelatinization. In this study, large-ring cyclodextrins (LR-CDs) were synthesized from potato starch (PS) by using 4-α-glucanotransferase and then added to PS to alleviate the increased viscosity during gelatinization. The results from rapid viscosity analyzer (RVA) demonstrated that the inclusion of 5 % (w/w) LR-CDs markedly reduced the peak viscosity (PV) and final viscosity (FV) of PS by 49.85 % and 28.17 %. In addition, there was a quantitative relationship between PV and LR-CDs. The equation was fitted as y = 2530.73×e−x/2.48+1832.79, which provided a basis for the regulation of PS viscosity. The mechanism of LR-CDs reducing the viscosity of PS was also studied. The results showed that the addition of LR-CDs inhibited the gelatinization of PS by enhancing orderliness and limiting water absorption, resulting in a decrease in viscosity. This study provides a novel method for reducing the viscosity of starch, which is helpful for increasing its concentration and reducing energy consumption in industrial applications.

Research on the synergistic flame retardation of epoxy resin through surface-modified aluminum diethylphosphinate in conjunction with DOPO and CFA

Surface modification of aluminum diethylphosphinate (ADP) was successfully achieved through the utilization of silane coupling agent KH-560. Simultaneously, the modified aluminum diethylphosphinate (K-ADP) served as the primary flame retardant, with 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) as the phosphorus-based flame retardant and charring‐forming agent (CFA) as the nitrogen-based synergistic flame retardant. This approach was employed to investigate the flame-retardant modification of epoxy resin. The optimal dosage of the surface modifier was investigated through moisture absorption test and viscosity measurements. Synergistic flame-retardant interactions among K-ADP, DOPO, and CFA were examined using techniques such as cone calorimetry test, thermogravimetric analysis, and residual char infrared analysis. The results indicated that the optimal dosage of KH-560 is 5%, resulting in a significant reduction in moisture absorption to 0.195%. At 80 °C, the addition of K-ADP leaded to only a 22.7% increase in system viscosity, demonstrating a notable viscosity reduction effect. When the addition of K-ADP is 14%, the Limiting Oxygen Index (LOI) value reached 30.5%, achieving a V-0 rating. Moreover, by maintaining the total addition at 14% and introducing DOPO and CFA, it is evident that most of samples meet UL-94 V-0 rating, with the LOI elevated to 32.2%. CCT results indicated a significant decrease in both average heat release rate and total smoke production, reduced by 24.1% and 7.0%, respectively. This notably enhanced the flame-retardant and smoke-suppressant properties of the EP composite material. The addition of K-ADP, DOPO, and CFA improved the mechanical performance of the EP composite material, surpassing the effectiveness of adding ADP individually.

A Novel Quantitative Evaluation Method for Viscosity Reduction Effect of Heavy Oil Cold Recovery Based on The Area Diffusion Process

After thermal recovery, the emulsification viscosity reduction technology for heavy oil cold recovery exhibits low energy consumption and low cost, making it a promising technology for ongoing heavy oil reservoir development. The evaluation and optimization of viscosity reducer is very important for the cold recovery of heavy oil. Prior research mostly employed the high-speed shear technique to measure viscosity following emulsion formation in order to evaluate viscosity reducers. This method ignores the seepage emulsification process under low dynamic conditions of formation, resulting in the selected viscosity reducer ' qualified but not ideal '. Based on the regional diffusion process, a quantitative evaluation method for cold recovery of heavy oil viscosity reduction is put forward. This method is used to simulate the static emulsification effect of heavy oil under real formation conditions, and quantitative evaluation is carried out. The outcomes demonstrate that, in comparison to the conventional assessment approach, this method is more accurate in selecting a viscosity reducer. Appropriately increasing the concentration of the viscosity reducer can improve the efficiency of viscosity reduction. The viscosity reduction effect improves with reservoir temperature. Heavy oil and viscosity reduction agent may be quickly matched using the prediction model of viscosity reduction in cold recovery of heavy oil developed by orthogonal experiment. At the same time, through field practice, the viscosity reducer chosen by this way has a good oil increase impact on oilfield production.

A synergistic dispersion strategy for high volume fraction slurry and high performance silicon nitride sintered components in digital light processing (DLP)-based vat photopolymerization

The digital light processing (DLP)-based vat photopolymerization enables the fabrication of intricate silicon nitride (Si3N4) components. However, challenges still persist in producing low-defect and high-performance ceramic parts at lower volume fractions. In this study, a new block copolymer was employed for the modification of Si3N4 powders. The rheological behavior, dispersant mechanism, curing properties, printing performance of green body, mechanical properties and Weibull modulus of the sintered sample were systematically investigated. The results indicated that the modifier characterized by the long molecular chains and CC double bonds adhered successfully to the surface of Si3N4 particles through hydrogen bonding, and the viscosity reduction effect of this modifier was ten times lower than that of the reported KH560 modifier. Besides, the synergistic dispersion effect achieved via the combination of the long chain modifier with a small molecular dispersant, facilitates the preparation of a 60 vol% (80.74 wt%) Si3N4 slurry. Subsequently, the tightly bonded interlayer of the green body and the complex Si3N4 sintered components with different volume fractions, high consistency and superb mechanical performance (the strength of 865.87 ± 54.35 MPa and the Weibull modulus of 18.49) were fabricated. These findings highlight the promising potential of the proposed modification approach for advancing the fabrication of high volume fraction and high-performance Si3N4 components.

Synthesis and emulsion stability of salt resistant viscosity reducer for heavy oil reservoirs with varying salinities

To address the inadequate salt resistance of viscosity reducers and their limited applicability to reservoirs with single salinity, we synthesized salt-resistant viscosity reducers PANxAn in this study. These compounds were derived from fatty alcohol polyoxyethylene ether acrylate, N-alkyl acrylamide, acrylamide, and 2-acrylamido-2-methylpropanesulfonic acid. The structures were identified using nuclear magnetic hydrogen spectroscopy. We investigated the effects of the hydrophilic group ethoxy-chain length (n = 14, 16, 18, 20 and 22) and hydrophobic group alkyl-chain length (x = 12, 14, 16, and 18) on the salt resistance, interfacial activity, wettability, interfacial viscoelasticity and emulsification viscosity reduction performance of the viscosity reducers. Futher, the structures of the viscosity reducers which can adapt to different salinities were determined. Based on the emulsification viscosity reduction effect, PAN14A16, PAN12A16, PAN12A18, PAN12A20/PAN16A16 and PAN12A22/PAN18A16 adapted to salinities range of 2 × 104-6 × 104, 4 × 104-8 × 104, 6 × 104-10 × 104, 8 × 104-12 × 104 and 10 × 104-14 × 104 mg/L, respectively. At the optimal salinity, PANxAn reduced the oil–water interfacial tension from 28.3 to 5.0 mN/m, dynamic contact angle from 130.0° to 61.0°, and heavy oil viscosity from 454.6 to 60.0 mPa·s with a viscosity reduction rate of 86.80 %. The synthesis of salt-resistant PANxAn provides theoretical guidance and application value for enhancing the recovery efficiency of viscosity-reducer flooding in high-salinity heavy oil reservoirs.

Rheological properties of warm mixed high viscosity asphalt at high and low temperatures.

The rheological properties of asphalt can well reflect its road performance, but the rheological properties of warm mix high viscosity asphalt (HVA) are unclear. In order to study the effect of warm mixing agent on rheological properties of HVA, two kinds of warm mixing agent EC120 (EC) and Evotherm M1 (M1) were selected to prepare warm mix HVA. The rheological properties of warm mix HVA at high temperature (135~195°C), medium temperature (0~80°C) and low temperature (-6~18°C) were studied by Brinell rotary viscosity test, dynamic shear rheological test (including temperature scanning, frequency scanning, linear amplitude scanning) and bending beam rheological test. The test results show that both EC and M1 have good viscosity reduction effect on HVA at high temperature, and can effectively reduce the construction temperature. At medium temperature, M1 can effectively improve the fatigue resistance of HVA, and the fatigue life can be increased by about 30% when the dosage is 0.6%. EC can increase the rutting factor of HVA and improve its resistance to deformation, but it will reduce its fatigue performance. When the dosage is 4%, the fatigue life will be reduced by about 9%. At low temperature, M1 can reduce the creep stiffness S, increase the creep rate m, and improve the low temperature performance of HVA, while EC has the opposite effect, weakening the low temperature performance of HVA. The results are helpful to understand the rheological properties of warm mix HVA and promote its application.

Experimental and Simulation Studies of Imidazolium Chloride Ionic Liquids with Different Alkyl Chain Lengths for Viscosity Reductions in Heavy Crude Oil: The Effect on Asphaltene Dispersion.

Heavy crude oil poses challenges in terms of extraction and transportation due to its high viscosity. In the pursuit of effective methods to reduce viscosity in heavy crude oil, this study investigates the potential of imidazolium chloride ionic liquids with varying alkyl chain lengths as viscosity reducers. The experimental results demonstrate that the addition of 1-dodecyl-3-methylimidazole chloride ([C12-MIM]Cl) leads to a maximum viscosity reduction of 49.87%. Solubility parameters were calculated based on characterization of the average molecular structure of the asphaltenes. The viscosity reduction effect is enhanced when the solubility parameter of the ionic liquid closely matches that of the asphaltene. The initial asphaltene deposition point of heavy crude oil is increased from 63% to 68% with the addition of 150 mg/L [C12-MIM]Cl. Furthermore, the average particle size of asphaltene deposits decreases from 79.35 μm to 48.54 μm. The viscosity of heavy crude oil is influenced by the aggregation of asphaltenes. The ability of ionic liquids, especially those with longer alkyl chains, to disperse asphaltene molecules and reduce viscosity has been confirmed through molecular dynamics and quantum mechanical simulations.

A Novel Prediction Model for Steam Temperature Field of Downhole Multi-Thermal Fluid Generator

Aiming at the low efficiency of heavy-oil thermal recovery, a downhole multi-thermal fluid generator (DMTFG) can improve the viscosity reduction effect by reducing the heat loss of multi-thermal fluid in the process of wellbore transportation. The steam generated by the MDTFG causes damage to the packer and casing, owing to the return upwards along the annular space passage of the oil casing. To mitigate this damage, a heat transfer model for multi-channel coiled tubing wells and a prediction model for the upward return of the steam temperature field in the annulus were established with the basic laws of thermodynamics. Models were further verified by ANSYS. The results indicate the following four conclusions. First of all, when the surface pressure is constant, the deeper the located DMTFG, the shorter the distance for the steam to return would be. It is easier to liquefy the steam. Second, the higher the temperature of the steam produced by the downhole polythermal fluid generator, the larger the upward distance of the steam would be. Third, the higher the steam pressure at the outlet of the downhole polythermal fluid generator, the smaller the distance of steam upward return would be. Finally, the larger the diameter of the multi-channel conversion piping, the greater the distance of the steam return would be. It is meaningful to provide valuable theoretical guidance for packer position designing in the field. Meanwhile, the study also provides a modeling basis for the subsequent study of artificial intelligence in the downhole temperature field.

Recovery mechanisms of shale oil by CO2 injection in organic and inorganic nanopores from molecular perspective

CO2 injection is the feasible method to enhance shale oil recovery and has attracted extensive attention in recent years. Since shale reservoir has omnipresent nanoscale pores, understanding the underlying CO2-EOR mechanisms at the nanoscale is of critical importance. In this work, we study the structural and dynamic properties of CO2/nC8 systems in organic kerogen and inorganic quartz nanopores by molecular dynamic simulation and clarify the dominant EOR mechanisms of CO2 injection in various mineral nanopores. We find a large positive slip velocity occurs when single-phase nC8 flows in quartz nanopore while it is no-slip boundary condition in kerogen nanopore. The CO2-regulated nC8 in quartz nanopore is the joint effect of slip, competitive adsorption and viscosity reduction. In the first stage, CO2 extracts the first adsorption layer of nC8 by competitive adsorption and forms a CO2 film on the quartz surface. The CO2 film reduces the slip velocity between nC8 and quartz surface and weakens the nC8 flow capacity. After CO2 adsorption is saturated, the CO2 mixes with nC8 in all flow regions and the effective viscosity of nC8 starts decreasing at this stage. The flow capacity of nC8 rises dramatically due to the viscosity reduction mechanism of CO2. In kerogen nanopore, it is no-slip boundary condition and CO2 mixes with nC8 in all flow regions directly instead of preferably adsorbed on the surface. Viscosity reduction is the dominant mechanism to affect nC8 flow behavior and nC8 flow capacity is enhanced monotonically as CO2 injection. Our study advances the understanding of the recovery mechanisms of shale oil by CO2 injection on nanoscale and provides the theoretical foundation for the optimization of CO2-EOR in shale oil reservoirs.

Multi-phase behavior and pore-scale flow in medium-high maturity continental shale reservoirs with Oil, CO2, and water

The application of CO2 to enhancing the recovery of continental shale oil has attracted considerable attention. However, the introduction of CO2 leads to intricate phase behavior and flow mechanisms. In this study, firstly, a three-phase equilibrium model is developed, with nano-confinement effects taken into consideration, to analyze the phase behavior of continental shale oil-CO2-water systems in both a bulk phase and nanopores. Building upon this, an improved pore network model is introduced to simulate steady-state oil–water flow while considering the alterations in fluid properties resulting from CO2 dissolution. The findings reveal that with the increase of CO2 injection, a transition from two phases of liquid and water to two phases of vapor and water, three phases of liquid, vapor and water, two phases of vapor and water, and ultimately a pure vapor phase occurs. The dissolution of CO2 exerts a pronounced impact on the composition and properties of the oil phase, and the viscosity and interfacial tension reduction effects play a central role in affecting the flow capacity. Nano-confinement effects facilitate the transfer of vapor-phase molecules into the water and oil phases, thus increasing the concentration of CO2 in the oil and water phases. The pore-scale flow results reveal that upon injection, water quickly traverses the larger pores. More smaller pores become accessible after CO2 dissolution, significantly boosting the extraction of shale oil from these smaller pores and slightly reducing the water output.

Preparation and performance study of anti mud polycarboxylic acid slump retaining agent

Anti-mud polycarboxylic acid slump retaining agent was prepared by copolymerization of ethylene glycol monovinyl polyethylene glycol ether, diethyl 4-vinylphenyl phosphate, 2-methyl-2-(4-vinylphenyl) propionic acid, unsaturated carboxylic acid (or unsaturated carboxylic anhydride) and unsaturated carboxylic ester under the action of initiator and molecular weight regulator. The effect of the slump retaining agent on the workability of fine aggregate concrete with different mud contents was tested, and the sensitivity of the slump retaining agent to the mud content of machine-made sand was evaluated. At the same time, the viscosity reduction performance of the slump retaining agent was evaluated by using the emptying time of the inverted slump cone and the flow time of V-funnel and L-box. The experimental results show that the synthesized anti-mud polycarboxylic acid slump retaining agent has favourable effects of anti-mud and viscosity reduction.

Experimental study on modified lotus stem biochar-based catalysts for heavy oil aquathermolysis

To obtain high-activity catalysts for aquathermolysis at low temperatures, a composite modification method of KOH and silane coupling agent KH570 was used to successfully prepare modified lotus stem biochar (MLSB), and six catalysts with different ZrO2 and MoO3 contents (5–30 %) were synthesized by impregnation method. MLSB and catalysts were analyzed by SEM, N2 adsorption and desorption isotherms, surface pore size, and FT-IR. The results revealed that the pores of raw lotus stem biochar were increased and enlarged, and some -OH on the surface was replaced by hydrophobic groups to form hydrophobic supports. Catalysts had hydrophobic and strong acidic sites. The catalytic activities were evaluated by aquathermolysis experiments. Catalysts exhibited satisfying abilities to catalyze aquathermolysis at low temperatures (130–200 °C). Specifically, 25 % ZrO2−MoO3/MLSB catalyst displayed the optimal heavy oil viscosity reduction rate (86.1 %) at 200 °C, which was attributed to hydrophobicity, more active components and strong acid sites. The highest viscosity reduction rate of heavy oil was obtained with 25 % ZrO2−MoO3/MLSB at 200 °C and a catalyst content of 3 wt%. Continuing to increase the catalyst content decreased the viscosity reduction rate, likely due to catalyst agglomeration hindering the contact between the active component and heavy oil. Moreover, the viscosity reduction effect of the catalyst increased with higher reaction temperatures. Additionally, a reaction network of aquathermolysis catalyzed by ZrO2−MoO3/MLSB was proposed. These findings contribute to the development of efficient catalytic systems for aquathermolysis and provide insights into the application of biochar-based catalysts in heavy oil viscosity reduction.

Experimental Study on Water-in-Heavy-Oil Droplets Stability and Viscosity Variations in the Dilution Process of Water-in-Heavy-Oil Emulsions by Light Crude Oil

The main objective of this study is to put forward effective schemes for alleviating reservoir choke caused by emulsification or Jamin’s effect using the dilution method by light crude oil, as well as sharply increased viscosity. In this study, water-in-heavy-oil (W/O) emulsions with varying water fractions were prepared with heavy oil from Bohai Bay, China. Mixtures of W/O emulsions and light crude oil samples (light oil and light heavy oil) with varied dilution ratio (1:9, 2:8, 3:7) are tested, respectively by the electron microscope and by the rheometer. W/O droplets’ distribution and viscosity variations are obtained to evaluate the emulsion stability and viscosity reduction effects by dilution. Results show that W/O droplets, size distribution range increases with the increase of water fractions. W/O droplets with larger size tend to be broken first in the dilution process. Light oil could reduce emulsions’ viscosity more effectively than light heavy oil. Viscosity reduction mechanisms by dilution could be concluded as the synergistic effects of dissolving heavy components and weakening oil–water film stability. Therefore, light oil is suggested as the optimal one for solving formation plugging. The poor performance of Richardson model is related to the re-emulsification between free water and crude oil favored by light heavy oil, and demulsification favored by light oil. The modified model shows a significant improvement in prediction accuracy, especially for W/O emulsions with large water fractions. This study demonstrates a promising and practical strategy of solving heavy oil well shutdown problems and viscosity increasing by injecting light crude oil in the thermal stimulation.