Effects of relative permeability change resulting from interfacial tension reduction on vertical sweep efficiency during the CO2-LPG hybrid EOR process

The addition of liquefied petroleum gas (LPG) to the CO₂ stream reduces interfacial tension (IFT) between the injected gas and the reservoir oil, and it changes the gas-liquid relative permeability by making it more water-wet, which affects not only the oil mobility, but also the vertical sweep efficiency. The reduction of the IFT decreases vertical sweep efficiency because it enhances the relative permeability of the solvent, resulting in an increase in the viscous gravity number. For CO₂-LPG enhanced oil recovery (EOR), oil recovery is enhanced by up to 47%, as compared to CO₂ flooding, when the relative permeability change caused by the IFT is not considered. By taking the vertical sweep-out caused by IFT and relative permeability change into consideration, this increase is reduced to 40%. These results indicate the importance of considering the relative permeability and IFT change when predicting the performance of the CO₂-LPG EOR process.     

Wettability alteration of carbonate reservoir rock using amphoteric and cationic surfactants: Experimental investigation

The objective of this study is to prove that altering the wettability of reservoir rocks by two surfactants (hexadecyl amino benzene sulfonic acid [HABSA] and cationic hexa decyl trimethyl ammonum bromide [CTAB]). Changing the wettability to preferentially water-wet condition will reduce the residual oil saturation (S_or). Because of reducing S_or, the percentage of recovered oil is increased. All surfactants were tested for their ability to alter the wettability of reservoir rocks. This alteration was measured based on the contact angle methods. Results of this study show that both amphoteric HABSA and CTAB surfactants alter the wettability of carbonate rocks from oil-wet to water-wet, while CTAB alters the wettability from oil-wet to water-wet more than HABSA. Also, recovery factor in CTAB injection was more than HABSA injection. Ultimately, the results show that the CTAB surfactant is more effective than HABSA surfactant to alter the wettability and improve oil recovery from carbonate reservoirs.     

Evaluation of CO2 enhanced oil recovery and sequestration potential in low permeability reservoirs,Yanchang Oilfield,China

Sequestrating CO₂ in reservoirs can substantially enhance oil recovery and effectively reduce greenhouse gas emission. To evaluate the potential of CO₂ enhanced oil recovery (EOR) and sequestration for Yanchang Oilfield in China, a screening standard which was suitable for CO₂-EOR and sequestration in Yanchang Oilfield was proposed based on its characteristics of strong heterogeneity, high water content and severe fluid channeling after water flooding. In addition, an efficient calculation method – stream tube simulation method was presented to figure out CO₂ sequestration coefficient and oil recovery factor. After screening and evaluating, it turned out that 148 out of 176 blocks in 22 oilfields were suitable for CO₂-EOR and sequestration. CO₂ flooding after water flooding can produce 180.21 × 10⁶ t more crude oil and sequestrate 223.38 × 10⁶ t CO₂. The average incremental oil recovery rate of miscible reservoirs was 12.49% and the average CO₂ sequestration coefficient was 0.27 t/t while the two values were 6.83% and 0.18 t/t for immiscible reservoirs. There are comparatively more reservoirs that are suitable for CO₂-EOR and sequestration in Yanchang Oilfield than normal, which can obviously enhance oil recovery and means a great potential for CO₂ sequestration. CO₂-EOR and sequestration in Yanchang Oilfield has a bright application prospect.     

Investigation of the effects of low-salinity waterflooding for improved oil recovery in carbonate reservoir cores

Water injection for both pressure maintenance and oil displacement is the most important secondary recovery method in sandstones. It has also been implemented with success in a few carbonate reservoirs, but because the most carbonate reservoirs worldwide are characterized as neutral to preferential oil-wet, normal waterflooding is usually not successful as an enhanced oil recovery (EOR) technique. It has been proved that seawater can be used as an EOR fluid for hot, fractured carbonate oil reservoirs since it is able to modify the wetting conditions and to enhance the oil recovery. The potential determining ions in seawater such as Ca²⁺, Mg²⁺, and SO₄^2- played a crucial role in altering the wettability from oil-wet to more water-wet condition because of their reactivity towards the carbonate surface. In this paper, the potential of low-salinity brine to enhance the oil recovery has been studied. Four flooding tests were conducted on both limestone cores containing anhydrite and chalk core containing no sulfate. It is observed that low-salinity brine had only effect on rocks containing anhydrite. The dissolution of anhydrite, CaSO₄, which is the source for SO₄^2-, is depending on salinity/composition of brine and the temperature. The dissolution of anhydrite normally increases as the temperature decreases. Lowering the salinity of injection brine increases the reactivity of the surface-active ions SO₄^2- and Ca²⁺.     

Co-optimization of CO2 sequestration and enhanced oil recovery in extra-low permeability reservoir in Shanbei

This article put forward a theoretical system, which is used to analyze co-optimization of CO₂ sequestration and enhanced oil recovery by using the methods or theories including the design of experiments, numerical simulation, net present value, and the response surface methods. A CO₂ flooding operation in an immiscible water-alternating-gas process of Shanbei extra-low permeability reservoir was estimated preliminarily by using the methods proposed in this article. The result shows that optimized values obtained from predicted values were in good agreement with the values obtained from the simulation model and it is possible to optimize a coupled CO₂ sequestration and enhanced oil recovery project.     

The effect of capillary-trapped CO2 on oil recovery and CO2 sequestration during the WAG process

This study investigated capillary-trapped CO₂ depending on the consideration of hysteresis effect in relative permeability for various water-alternation-gas (WAG) operating conditions to ascertain the oil production process. From the simulation results of CO₂ WAG flooding method, the trapped CO₂ led to prevent water-flow, in which CO₂ acts as a gas blocker near the well. It caused the injection pressure increase during water injection period. As the trapped CO₂ in pores increased, the reservoir pressure was also increased and maintained above minimum miscibility pressure (MMP). Ultimately, it was concluded that the reservoir was kept under miscible conditions throughout WAG process, reducing residual oil and increasing oil recovery.     

Close-packed SiO2/poly(methyl methacrylate) binary nanoparticles-coated polyethylene separators for lithium-ion batteries

In an endeavour to improve not only the thermal shrinkage but also the electrochemical performance of separators in lithium-ion batteries, a novel composite separator is developed, i.e., a close-packed SiO₂/poly(methyl methacrylate) (PMMA) binary nanoparticles-coated polyethylene (PE) separator. The introduction of SiO₂ nanoparticles to the coating layer effectively suppresses thermal shrinkage of the composite separator. In contrast to a SiO₂/PMMA coating layer having a film-shaped PMMA binder, the SiO₂/PMMA binary nanoparticle coating layer employs PMMA particles as a binder. As a consequence, a highly porous structure, i.e., well-connected interstitial voids, is formed between the binary SiO₂ and PMMA nanoparticles. The unique porous morphology allows favourable liquid electrolyte wettability and facile ionic conduction, which play a crucial role in improving cell performance such as the discharge capacity and the C-rate capability of the composite separator.     

Application of different EOR techniques for the energy and recovery of Ashal’cha oil field

In this research, utilizing the reservoir and produced oil data, different enhanced oil recovery (EOR) techniques known as in-situ combustion, CO₂ flooding, and steam flooding were applied for Ashal’cha oil field in Republic of Tatarstan, Russia. For this purpose, In-Situ Combustion Predictive Model (ICPM), CO₂ Miscible Flood Predictive Model (CO₂PM) and Steam-flood Predictive Model (SFPM) are used. In addition to oil recovery, economic analysis of the discussed EOR applications was also conducted. By using the oil price forecast for 10 years, each EOR method is analyzed using their expenses and outcomes separately. Comparison among the EOR applications regarding the oil production, and economic feasibility was also given. Taking the reservoir and produced oil characteristics, oil production rate and economical payout time into account, it was observed that in-situ combustion is the most feasible and practical EOR method for Ashal’cha oil field.     

Impact of wettability on storage and recovery of hydrogen gas in the lesueur sandstone formation (Southwest hub project,Western Australia)

Geological storage has been proposed as a new technology to temporarily store significant amounts of hydrogen (H₂) gas in depleted gas reservoirs, underground salt caverns, or saline aquifers. Often, such subsurface reservoirs naturally contain trace amounts of organic acids, and these compounds can considerably alter the wettability of reservoir rocks, causing them to become less water-wet. We carried out Molecular Dynamics (MD) simulations of contact angles in a quartz-brine-H₂ system to evaluate wettability in realistic subsurface situations. MD simulations suggest that Humic acid makes quartz more hydrophobic, which can affect the overall behaviour of the storage reservoir. For the first time, this effect was experimentally investigated for a natural sandstone reservoir from the South West Hub Project, i.e., the Lesueur Sandstone (LS) formation. Multi-stage core flooding experiments were conducted on the same LS plug to investigate the impact of wettability alteration on initial and residual hydrogen saturation/trapping at depth. First, consecutive brine-H₂ drainage-imbibition cycles were carried out on the natural sample; the result indicated that the rock-brine-H₂ system was essentially water-wet. Then, the sample was aged in Humic acid with a molarity of 10⁻² M for 42 days at 5 °C and 0.1 MPa. The wettability of the storage system shifted toward a less water-wet state, i.e., more hydrophobic. As a result of Humic acid ageing, the initial hydrogen saturation reduced from 29% to 15%, and the residual hydrogen trapping reduced from 23% to 11%. This is attributed to a change induced in the capillary force (i.e., snap-off) controlled by wettability and pore size. In addition, the wettability change induced by Humic acid increased the hydrogen recovery rate from 20.7% to 26.7%.     

Experimental studies of surfactant-polymer flooding: An application case investigation

A great deal of oil field is currently produced using water flooding and the water cut has reached a high level, which requires enhanced oil recovery (EOR) techniques to improve the recovery. Surfactant-polymer (SP) flooding is the combination of surfactant flooding and polymer flooding. The polymer is added to increase the viscosity and viscoelasticity of the fluid while the surfactant is included to decrease the oil–water interfacial tension and change the wettability. Although the mechanism of SP flooding has been deeply investigated, the application of SP flooding on a specific oil field requires the selection of optimal SP system. Therefore, for the first time, we performed a series of experiments to determine the optimal SP system for high water-cut oil field. In the injection capability experiment, we observe that the SP system is injected into the core with less resistance compared with single polymer solution. In the flooding experiment, regardless of the polymer types, the improvement of recovery becomes significant when the injected PVs increases. SP flooding shows the higher improvement of recovery compared with single polymer flooding or surfactant flooding. Based on the performance of recovery improvement, we recommend the optimal SP system for the studied case is the combination of DQ-TSRP01 polymer and surfactant. The optimal injection parameters of this SP system are 1500 mg/L polymer concentration, 0.3 injection PV and the injection timing of 96% water cut. The finding of this study can help for better understanding of the application of SP flooding in high water-cut oil field production.     

Immiscible CO2 Flooding through Horizontal Wells

Abstract

The CO₂ immiscible process is a potentially viable method of enhanced oil recovery (EOR) for heavy oil reservoirs. In an immiscible CO₂ process, part of the injected CO₂ is absorbed into the reservoir fluids and part forms a free-gas phase in the reservoir. Three groups of well configurations were mainly used: (1) vertical injection and vertical production wells, (2) vertical injection and horizontal production wells, and (3) horizontal injection and horizontal production wells. In immiscible CO₂ injection, highest recovery was obtained by vertical injection-horizontal production (VI-HP), followed by vertical injection-vertical production (VI-VP), and the least by horizontal injection-horizontal production (HI-HP). In VI-HP well configuration, the best recovery was obtained as 15.1% OOIP. In continuous CO₂ injection experiments, oil recovery for the VI-HP well configuration was higher than that of the other well configurations. The lowest ultimate recovery was obtained from HI-HP well configuration. The distance between the horizontal injector and horizontal producer was another important factor for the displacement of oil. In all runs, CO₂ breakthrough occurred very early, showing the dominance of viscous forces and relatively small effect of mass transfer between CO₂ and oil. The total oil recovery varied considerably because of the differences in injection rates and because of the unstable displacement. As a whole, oil recovery increased with an increase in the injection rate of CO₂. The cumulative gas-oil ratio (GOR) appeared to be sensitive to the gas injection rate for all well configurations. An increase in oil recovery with injection rate during initial stages of the runs was affected by the cumulative GOR.     

Preparation and characterization of coke resistant Ni/SiO2 catalyst for carbon dioxide reforming of methane

Silica supported Ni catalyst is highly active for the CO₂ reforming of methane but it has poor stability due to coke formation. In this work, a glow discharge plasma was applied for the decomposition of nickel nitrate on the SiO₂ support, followed by thermal calcination in air. The plasma treatment enhances the interactions between the Ni particles and the silica and significantly improves the Ni dispersion. The plasma-treated Ni/SiO₂ catalyst exhibits comparable activity to the Ni/SiO₂ catalyst prepared by the thermal method without plasma treatment. The coke resistance of the Ni/SiO₂ catalyst is significantly enhanced by the plasma treatment.     

Hydrogen sensing characteristics of Pd/SiO2-nanoparticles (NPs)/AlGaN metal-oxide-semiconductor (MOS) diodes

A Pd/SiO₂-nanoparticles (NPs)/AlGaN metal-oxide-semiconductor (MOS) structure is used to fabricate interesting Schottky diode-type hydrogen sensors. The employment of SiO₂-NPs could effectively increase the specific surface area of Pd catalytic metal and the Schottky barrier height. Good hydrogen sensing performance is obtained. Experimentally, as compared to a conventional Pd/AlGaN MS diode, a significant 34.5-fold improvement on hydrogen sensing response is obtained under an introduced 1% H₂/air gas at 300 K when a 10 wt% concentration of SiO₂-NPs is employed in the studied device. Yet, the increase in SiO₂-NP concentration relatively deteriorates the ability to detect very low hydrogen concentration levels (≦1 ppm H₂/air). In addition, the increase in SiO₂-NP concentration creates a decrease and increase on response and recovery time constants of transient behaviors, respectively.     

Effect of inert particle concentration on the operation of a microbial fuel cell

Considering the promising application of microbial fuel cells (MFCs) in the wastewater treatment, the inherent solid particles in the wastewater may affect the MFC performance. In this paper, the effect of inert particle concentration on the operation of MFCs is investigated by adding silicon dioxide (SiO₂) particles into the anolyte. The results show that the existing SiO₂ particles in the anolyte result in a decreased active biomass and a reduced electrochemical activity of the biofilm. The anode ohmic resistance is almost the same for MFCs with various SiO₂ particle concentrations in the anolyte, while an increase in the charge transfer resistance is observed. A small amount of inert particles have little influence on the MFC. However, when the MFC is operated with the anolyte containing more than 500 mg L⁻¹ SiO₂ particles, the performance decreases significantly due to the low electrochemical activity and high internal resistance of the anode.     

Combustion synthesis of SiO2 on the aluminum plate

The approach of utilizing combustion synthesis to make fine particles of SiO₂, Al₂O₃ and TiO₂ is a quite modern technology. Through the chemical reaction in post-flame region, fine SiO₂ particles can be formed with high purity on plate surface. Therefore, the combustion synthesis of SiO₂ powders is an important area for further research and development, especially for the application of SiO₂ in the semiconductor industry. This investigation proposes an experimental approach (i.e., a gas-phase combustion synthesis) using two different kinds of organic compounds, Hexamethyldisilazane (HMDSA) and Hexamethyldisioxane (HMDSO), as the silicon precursors. A premixed gas burner is chosen with C₃H₈ as fuel, air as oxidant and part of the air was used as the carrying gas to entrain HMDSA/HMDSO vapor into the combustible mixture. Observations show that the C₃H₈/air flame changed color from a pale-blue flame to light yellow and then orange when different amounts of precursors were introduced. Through the chemical reaction in the post-flame region, fine SiO₂ particles were formed in the gas phase and then quenched and collected on an aluminum flat plate. The objective of this paper is to study the effects of HMDSO and HMDSA concentrations and flame temperatures on the synthesis of SiO₂ particles.     

Adsorption of a nonionic surfactant onto a silica surface

Chemical flooding is technically feasible to increase oil recovery from depleted sandstone reservoirs with low pressure. Polymer-surfactant flooding is a potential process in the chemical flooding methods for enhanced oil recovery (EOR) in sandstone porous media. However, chemical additive cost and surfactant loss due to adsorption on the reservoir rock are the main concerns in this type of EOR processes. This paper presents adsorption equilibrium of a natural surfactant, Zyziphus spina-christi, onto a real sandstone reservoir. Batch adsorption experiments were carried out to figure out the impacts of adsorbent dose on adsorption performance. The equilibrium adsorption data were analyzed with two common adsorption models and it was found that the Freundlich model is a pretty good fit for adsorption equilibrium of Z. spina-christi based on the value of determination coefficient (R²). Results from this study are instructive for appropriate selection of surfactants in design of EOR processes and reservoir stimulation plans for sandstone reservoirs.     

Combustion-impregnation preparation of Ni/SiO2 catalyst with improved low-temperature activity for CO2 methanation

Exploiting Ni-based catalysts with excellent low-temperature activity is significant for CO₂ methanation, which is a promising route to CO₂ utilization. In this work, a facile combustion-impregnation method was developed to prepare the SiO₂ supported Ni catalysts. Small Ni particles (around 6 nm) and massive Ni–SiO₂ interface could be obtained due to the “combustion” process. The H₂-temperature programmed desorption (H₂-TPD) revealed the existence of Ni–SiO₂ interface and confirmed the high Ni dispersion obtained by this method, which were vital for the activation of reactant. Moreover, more medium basic sites which were beneficial for the CO₂ activation could also be created. In comparison with the reference Ni/SiO₂ catalyst prepared by the conventional impregnation method, much higher CO₂ conversion (66.9%) and more superior selectivity to CH₄ (94.1%) were achieved with the Ni/SiO₂-Gly catalyst at 350 °C. Additionally, it was also found that glucose, citric acid and glycine were all effective fuels for this combustion-impregnation method, and the as-prepared catalysts all exhibited greatly improved low-temperature activity. Therefore, this work represents an important step toward developing Ni-based catalysts for CO₂ methanation by a promising wide-used method.     

Methanation over Ni/SiO2: Effect of the catalyst preparation methodologies

We confirmed here that the catalyst preparation methodologies have a significant effect on the activity and stability of Ni/SiO₂ catalyst for methanation of syngas (CO + H₂). Catalyst characterizations using X-ray diffraction (XRD), hydrogen temperature-programmed reduction (H₂-TPR) and transmission electron microscope (TEM) were performed to investigate the structure and performance of the catalysts. The activity and stability of catalysts prepared by thermal decomposition and dielectric-barrier discharge (DBD) plasma decomposition of nickel precursor were compared. The plasma decomposition results in a high dispersion, an enhanced interaction between Ni and the SiO₂ support, as well as less defect sites on Ni particles. Enhanced resistance to Ni sintering was also observed. In addition, the plasma prepared catalyst effectively inhibits the formation of inactive carbon species. As a result, the plasma prepared catalyst exhibits significantly improved activity with enhanced stability.     

Utilization of produced gas of CO2 flooding to improve oil recovery

Large amounts of mixed gas containing CO₂ and hydrocarbon would be produced during CO₂ flooding. Injecting the produced gas back to reservoir can not only make full use of CO₂, but also can reduce air contamination. Taking produced crude oil and gases with different CO₂ concentration from Jilin oilfield as examples in this paper, the phase behavior and the physical properties of live oil-gas system were measured with a visible PVT apparatus. In terms of oil viscosity reduction and swelling, the gas with high CO₂ concentration was found to be substantially effective. Furthermore, comparative slim tube tests of the oil recovery performance using the five kinds of gases under different operating pressure were conducted in one-dimensional model. Results indicate that displacement efficiency increases linearly with the increasing CO₂ content in the recycle gas; displacement efficiency increases with operating pressure under immiscible conditions. Re-injecting produced gas with relative high CO₂ concentration back to reservoir is a method both time-saving and cost-effective.     

适合大庆油田的无碱表面活性剂性能评价研究

随着油田不断开发,大庆油田开发对象正逐渐从一类油层向渗透率低、黏土矿物含量较高的二、三类油层转变,但逐步进入工业化推广阶段的三元复合驱中碱的存在会加剧对二、三类油层的伤害,因此弱碱化、无碱化成为了复合驱技术的发展方向.针对大庆油田二类油层油水条件,采用AFS-A和AFS-B无碱表面活性剂复合体系开展了二元复合驱室内研究.实验结果表明:这两种无碱表面活性剂复合体系均可在活性剂浓度为0.05％～0.3％(质量分数)范围内与大庆原油形成10-3,N/m数量级界面张力,但AFS-B复合体系亲水性较强,AFS-A复合体系亲油性较强,AFS-B复合体系抗吸附性能要好于AFS-A复合体系;驱油效率方面,在水驱基础上,AFS-A复合体系化学驱平均采收率为17.28％,AFS-B复合体系化学驱平均采收率为19.81％.