Determination of Minimum Miscibility Pressure of CO2–Oil System: A Molecular Dynamics Study

CO₂ enhanced oil recovery (CO₂-EOR) has become significantly crucial to the petroleum industry, in particular, CO₂ miscible flooding can greatly improve the efficiency of EOR. Minimum miscibility pressure (MMP) is a vital factor affecting CO₂ flooding, which determines the yield and economic benefit of oil recovery. Therefore, it is important to predict this property for a successful field development plan. In this study, a novel model based on molecular dynamics to determine MMP was developed. The model characterized a miscible state by calculating the ratio of CO₂ and crude oil atoms that pass through the initial interface. The whole process was not affected by other external objective factors. We compared our model with several famous empirical correlations, and obtained satisfactory results—the relative errors were 8.53% and 13.71% for the two equations derived from our model. Furthermore, we found the MMPs predicted by different reference materials (i.e., CO₂/crude oil) were approximately linear (R² = 0.955). We also confirmed the linear relationship between MMP and reservoir temperature (T_R). The correlation coefficient was about 0.15 MPa/K in the present study.     

Effects of CO2 Injection on Phase Behavior of Crude Oil

CO₂ flooding is a win-win technology, sequestrating greenhouse CO₂ while producing a significant amount of crude oil to help defray the cost of CO₂ sequestrating and enhancing oil recovery. However, due to the difference of sedimentary environment and poor properties of formations, physical properties of the crude oil and the effect of CO₂ flooding are not always satisfactory in most oilfields of China. Therefore, in this article, to improve the understanding of the oil recovery mechanisms and feasibility of CO₂ flooding in China, based on the oil and gas of Mao-3 oilfields, phase behavior of the CO₂ and crude oil system was investigated. Parameters like saturated pressure, volume factor, gas oil ratio, and viscosity were measured and their relationships analyzed. Results show that crude oil of Mao-3 reservoir and CO₂ has good mutual dissolution under reservoir conditions, and CO₂ could expand the oil and reduce the oil viscosity greatly. As a result, formation energy could be enhanced and flow characteristics of the oil could be improved by CO₂ flooding.     

Laboratory Study on Low Gas/Liquid Ratio Foam Flooding for Zhuangxi Heavy Oil

Considering the high cost and injection pressure of conventional foam flooding, foam flooding with low gas/liquid ratio was proposed to enhance the heavy oil recovery. A foamer containing 0.2 wt% α -olefin sulfonate, 0.1 wt% HPAM and 0.5 wt% Na₂CO₃ was selected for Zhuangxi heavy oil. Then the foam stability and low gas/liquid ratio foam flooding were studied via micro model and sand pack experiments. The results indicate that the foam is much more stable in heavy oil than in diesel; in flooding tests, this foamer with gas/liquid ratio of 0.2:1 increases the oil recovery by 39.8%, which is nearly 11% higher than ASP solution in terms of the same injection volume (0.3PV) and agents.     

Oil-CO2 MMP Determination in Competition of Neural Network,Support Vector Regression,and Committee Machine

Oil-CO₂ minimum miscible pressure (MMP) has significance in selecting appropriate reservoir for miscible gas injection and greatly governs performance of local displacement. Accurate determination of MMP is very expensive, time-consuming, and labor intensive. Therefore, the quest for a method to determine MMP accurately and save time and money is necessary. This study held a competition between neural network and support vector regression models and assessed their performance in prediction of MMP for both pure and impure miscible CO₂ injection. Subsequently, a committee machine was constructed based on divide and conquer principle to reap benefits of both model and increases the precision of final prediction. Results indicated committee machine performed more satisfyingly compared with individual intelligent models performing alone.      

Mechanism of Produced Gas Reinjection During CO2 Flooding by Chromatographic Analysis

CO₂ flooding process has been a proven valuable method that could not only enhance oil recovery but also store greenhouse gas. However, CO₂ source greatly restrict its application in China. In this article, based on the produced oil and gas of Jilin oilfield, slim tube tests were conducted to study the feasibility of the produced gas reinjection without separation. In addition, according to the phenomenon of the experiment, displacement process was divided into three stages. Chromatographic analysis was conducted to study the mechanism of production gas reinjection during CO₂. Results indicate that components of the produced oil change along with CO₂ content, displacement pressure and production stages.     

Nanofluid in Hydrophilic State for EOR Implication Through Carbonate Reservoir

More than 50% of oil is trapped in petroleum reservoirs after applying primary and secondary recovery methods for removal. Thus, to produce more crude oils from these reservoirs, different enhanced oil recovery (EOR) approaches should be performed. In this research, the effect of hydrophilic nanoparticles of SiO₂ at 12 nm size, in (EOR) from carbonate reservoir is systematically investigated. Using this nanoparticle, we can increase viscosity of the injection fluid and then lower the mobility ratio between oil and nanofluid in carbonate reservoirs. To this end, a core flooding apparatus was used to determine the effectiveness and robustness of nanosilica for EOR from carbonate reservoirs. These experiments are applied on the reservoir carbonate core samples, which are saturated with brine and oil that was injected with nanoparticles of SiO₂ at various concentrations. The output results depict that, with increasing nanoparticle concentration, the viscosity of the injection fluid increases and results in decreased mobility ratio between oil and nanofluid. The results confirm that using the nanoparticle increases the recovery. Also, increasing the nanoparticle concentration up to 0.6% increases the ultimate recovery (%OOIP), but a further increase to 1.0 does not have a significant effect.     

The Wettability Alteration and the Effect of Initial Rock Wettability on Oil Recovery in Surfactant-based Enhanced Oil Recovery Processes

Wettablity alteration of rock surface is an important mechanism for surfactant-based enhanced oil recovery (EOR) processes. Two salt and temperature-tolerant surfactant formulations were developed based on the conditions of high temperature (97–120°C) and high salinity (20 × 10⁴ mg/L) reservoirs where a surfactant-based EOR process is attempted. Both the two sufactant formulations can achieve ultralow interfacial tension level (≤10^?3 mN/m) with crude oil after aging for 125 days at reservoir conditions. Wettability alteration of core slices induced by the two surfactant formulations was evalutated by measuring contact angles. Core flooding experiments were carried out to study the influence of initial rock wettabilities on oil recovery in the crude oil/surfactant/formation water/rock system. The results indicated that the two formulations could turn oil-wet core slices into water-wet at 90–120°C and 20 × 10⁴ mg/L salinity, while the water-wet core slices retained their hydrophilic nature. The core flooding experiments showed that the water-wet cores could yield higher oil recovery compared with the oil-wet cores in water flooding, surfactant, and subsequent water flooding process. The two surfactant formulations could successfully yield additional oil recovery in both oil-wet and water-wet cores.     

Rheological properties of surface-modified nanoparticles-stabilized CO2 foam

This study investigates the rheological properties of surface-modified nanoparticles-stabilized CO₂ foam in porous media for enhanced oil recovery (EOR) applications. Due to the foam pseudo-plastic behavior, the foam apparent viscosity was estimated based on the power law constitutive model. The results show that foam exhibit shear-thinning behavior. The presence of surface-modified silica nanoparticles enhanced the foam bulk apparent viscosity by 15%. Foam apparent viscosity in the capillary porous media was four times higher than that in capillary viscometer, and foam apparent viscosity increased as porous media permeability increases. The high apparent viscosity of the surface-modified nanoparticles-stabilized foam could result in effective fluid diversion and pore blocking processes and enhance their potential applications in heterogeneous reservoir.     

Comparison of three models for permeation of CO2/CH4 mixtures in poly(phenylene oxide)

Two models for the permeability of pure gases have been extended to include binary gas mixtures. The first is an extension of a pure gas permeability model, proposed by Petropoulos, which is based on gradients of chemical potential. This model predicts the permeability of components in a gas mixture solely on the basis of competition for sorption sites within the polymer matrix. The second mixed gas model follows an earlier analysis by Barrer for pure gases which includes the effects of saturation of Langmuir sites on the diffusion as well as the sorption processes responsible for permeation. This generalized “competitive sorption/diffusion” model includes the effect of each gas component on the sorption and diffusion of the other component in the mixture. The flux equations from these two models have been solved numerically to predict the permeability of gas mixtures on the basis of pure gas sorption and transport parameters. Both the mixed gas Petropoulos and competitive sorption/diffusion model predictions are compared with predictions from the earlier simple competitive sorption model based on gradients of concentration. An analysis of all three models is presented for the case of CO₂/CH₄ permeability in poly(phenylene oxide) (PPO). As expected, the competitive sorption/diffusion model predicts lower permeability than either of the models which consider only competitive sorption effects. The permeability depression of both CO₂ and CH₄ predicted by the competitive sorption/diffusion model is roughly twice that predicted by the competitive sorption model, whereas the mixed gas Petropoulos model predictions for both gases lie between the other two model predictions. For the PPO/CO₂/CH₄ system, the methane permeability data lie above the predictions of all three models, whereas CO₂ data lie below the predictions of all models. Consequently, the competitive sorption/diffusion model gives the most accurate prediction for CO₂, while the simple competitive sorption model is best for methane. The effects of mixed gas sorption, fugacity, and CO₂-induced dilation were considered and do not explain the inaccuracies of any of the models. The relatively small errors in mixed gas permeability predictions using either of the three models are likely to be related to “transport plasticization” of PPO owing to high levels of CO₂ sorption and its effect on polymer segmental motions and gas diffusivity.     

Rheological properties and enhanced oil recovery performance of a novel sulfonate polyacrylamide

A novel hydrosoluble sulfonate copolymer (SPAM) containing sulfonic acid groups was synthesized under mild conditions with Acrylamide (AM), 2-(Dimethylamino) ethyl methacrylate (DMAEMA) and 2-methyl-2-[(1-oxo-2-propenyl)amino]-1-propane sulfonic acid (AMPS) as monomers by segmentation initiation with 2,2'-azobis[2-methylpropionamidine] dihydrochloride and redox initiation system, respectively. The structures of copolymers were characterized by infrared (IR) spectroscopy, ¹H NMR spectroscopy and thermogravimetric analysis. The rheological properties of the copolymer solution at different shear rate, temperature and salt concentration were investigated. The shear-tolerance, temperature-tolerance and salt-tolerance of the novel synthetic hydrosoluble sulfonate copolymer are improved remarkably compared with partially hydrolyzed polyacrylamide (HPAM). The synthetic copolymer solution possesses a higher viscosity retention rate (53.3%) than HPAM (35.3%) at the total salinity of 20000 mg/L when temperature changed from 30°C to 99°C. The enhanced oil recovery (EOR) of the synthetic copolymer was performed by core flood, and the EOR degree of the synthetic copolymer in the 20000 mg/L salt solution at 80°C was better than that of HPAM. Compared with HPAM flooding, the EOR with the synthetic copolymer flooding was increased by 6.8% at 80°C.     

CO_2 residual concentration of potassium-promoted hydrotalcite for deep CO/CO_2 purification in H_2-rich gas

Elevated-temperature pressure swing adsorption is a promising technique for producing high purity hydrogen and controlling greenhouse gas emissions. Thermodynamic analysis indicated that the CO in H_2-rich gas could be controlled to trace levels of below 10 ppm by in situ reduction of the CO_2 concentration to less than 100 ppm via the aforementioned process. The CO_2 adsorption capacity of potassiumpromoted hydrotalcite at elevated temperatures under different adsorption(mole fraction, working pressure) and desorption(flow rate, desorption time, steam effects) conditions was systematically investigated using a fixed bed reactor. It was found that the CO_2 residual concentration before the breakthrough of CO_2 mainly depended on the total amount of purge gas and the CO_2 mole fraction in the inlet syngas.The residual CO_2 concentration and uptake achieved for the inlet gas comprising CO_2(9.7 mL/min) and He(277.6 mL/min) at a working pressure of 3 MPa after 1 h of Ar purging at 300 mL/min were 12.3 ppm and0.341 mmol/g, respectively. Steam purge could greatly improve the cyclic adsorption working capacity, but had no obvious benefit for the recovery of the residual CO_2 concentration compared to purging with an inert gas. The residual CO_2 concentration obtained with the adsorbent could be reduced to 3.2 ppm after 12 h of temperature swing at 450 °C. A new concept based on an adsorption/desorption process, comprising adsorption, steam rinse, depressurization, steam purge, pressurization, and high-temperature steam purge, was proposed for reducing the steam consumption during CO/CO_2 purification.     

Hydrophobically Associating Polymers Dissolved in Seawater for Enhanced Oil Recovery of Bohai Offshore Oilfields

As compared to China’s overall oil reserves, the reserve share of offshore oilfields is rather significant. However, offshore oilfield circumstances for enhanced oil recovery (EOR) include not just severe temperatures and salinity, but also restricted space on offshore platforms. This harsh oil production environment requires polymers with relatively strong salt resistance, solubility, thickening ability, rapid, superior injection capabilities, and anti-shearing ability. As a result, research into polymers with high viscosity and quick solubility is recognized as critical to meeting the criteria of polymer flooding in offshore oil reservoirs. For the above purposes, a novel hydrophobically associating polymer (HAP) was prepared to be used for polymer flooding of Bohai offshore oilfields. The synthetic procedure was free radical polymerization in aqueous solutions starting at 0 °C, using acrylamide (AM), acrylic acid (AA), 2-acrylamido-2-methylpropane sulfonic acid (AMPS), and poly(ethylene glycol) octadecyl methacrylate (POM) as comonomers. It was discovered that under ideal conditions, the molecular weight of HAP exceeds 2.1 × 10⁷ g⋅mol⁻¹. In a simulated reservoir environment, HAP has substantially greater solubility, thickening property, and salt resistance than conventional polyacrylamide (HPAM), with equivalent molecular weight. Finally, the injectivity and propagation of the two polymers in porous media were investigated. Compared with HPAM, which has a similar molecular weight, HAP solution with the concentration of 0.175% had a much better oil displacement effect in the porous medium, which can enhance oil recovery by 8.8%. These discoveries have the potential to pave the way for chemical EOR in offshore oilfields.     

CO2 Mobility and CO2/Brine Interfacial Tension Reduction by Using a New Surfactant for EOR Applications

The synthesis and use in enhanced oil recovery applications of a novel CO₂-philic surfactant derived from maleic anhydride and 2-butyl-1-octanol is reported. The synthesis involved the esterification of maleic anhydride to produce diester followed by sulfonation of the esterified product. The esterification reaction parameters were optimized for the maximum yield of 98.4%. By employing a silica sulfuric acid catalyst, the reaction kinetics of esterification were also investigated. The activation energy was found to be 45.58 kJ/mol. The sulfonation reaction of the esterified product was performed by using sodium bisulfite, and a yield of 82% of surfactant was achieved. The synthesized surfactant lowered the interfacial tension between CO₂/brine to 3.1 mN/m and effectively reduced the CO₂ mobility. This surfactant has a great potential to be used for CO₂ mobility control for CO₂?EOR applications.      

CH4, CO2和H2O在非金属原子修饰石墨烯表面的吸附

煤层气(矿井瓦斯)是一种有望替代传统化石燃料，如煤、石油和天然气的非常规气体. 作为可得的清洁能源，它的利用被认为是节能和经济的选择. 在本工作中，非金属原子X(X=H，O，N，S，P，Si，F，Cl)修饰的石墨烯(Gr)被用来代表具有结构异性的煤表面模型. 通过密度泛函理论系统地研究了煤层气组分Y(Y=CH₄，CO₂，H₂O)在非金属原子修饰石墨烯上的吸附作用. 结果表明Y在非金属原子修饰石墨烯上的吸附均为物理吸附. 态密度和差分电荷密度共同表明了这种弱的相互作用.其中，H和Cl对CH₄的作用较大； N、O、F、Cl对CO₂的作用较强； N，Cl对H₂O的影响不容忽视. 总的来说，吸附能大小依次为：H₂O>CO₂>CH₄. 因此，在CH₄富集的煤层里注入H₂O或CO₂可以与CH₄形成竞争吸附，进而提高煤层气采收率. 本工作提供了在分子水平下煤层气与非金属原子修饰石墨烯之间的相互作用的详情，并为煤层瓦斯的开采与分离提供了有用的信息.     

CH4, CO2和H2O在非金属原子修饰石墨烯表面的吸附

煤层气(矿井瓦斯)是一种有望替代传统化石燃料，如煤、石油和天然气的非常规气体. 作为可得的清洁能源，它的利用被认为是节能和经济的选择. 在本工作中，非金属原子X(X=H，O，N，S，P，Si，F，Cl)修饰的石墨烯(Gr)被用来代表具有结构异性的煤表面模型. 通过密度泛函理论系统地研究了煤层气组分Y(Y=CH₄，CO₂，H₂O)在非金属原子修饰石墨烯上的吸附作用. 结果表明Y在非金属原子修饰石墨烯上的吸附均为物理吸附. 态密度和差分电荷密度共同表明了这种弱的相互作用.其中，H和Cl对CH₄的作用较大； N、O、F、Cl对CO₂的作用较强； N，Cl对H₂O的影响不容忽视. 总的来说，吸附能大小依次为：H₂O>CO₂>CH₄. 因此，在CH₄富集的煤层里注入H₂O或CO₂可以与CH₄形成竞争吸附，进而提高煤层气采收率. 本工作提供了在分子水平下煤层气与非金属原子修饰石墨烯之间的相互作用的详情，并为煤层瓦斯的开采与分离提供了有用的信息.     

CH4, CO2和H2O在非金属原子修饰石墨烯表面的吸附

煤层气(矿井瓦斯)是一种有望替代传统化石燃料，如煤、石油和天然气的非常规气体. 作为可得的清洁能源，它的利用被认为是节能和经济的选择. 在本工作中，非金属原子X(X=H，O，N，S，P，Si，F，Cl)修饰的石墨烯(Gr)被用来代表具有结构异性的煤表面模型. 通过密度泛函理论系统地研究了煤层气组分Y(Y=CH₄，CO₂，H₂O)在非金属原子修饰石墨烯上的吸附作用. 结果表明Y在非金属原子修饰石墨烯上的吸附均为物理吸附. 态密度和差分电荷密度共同表明了这种弱的相互作用.其中，H和Cl对CH₄的作用较大； N、O、F、Cl对CO₂的作用较强； N，Cl对H₂O的影响不容忽视. 总的来说，吸附能大小依次为：H₂O>CO₂>CH₄. 因此，在CH₄富集的煤层里注入H₂O或CO₂可以与CH₄形成竞争吸附，进而提高煤层气采收率. 本工作提供了在分子水平下煤层气与非金属原子修饰石墨烯之间的相互作用的详情，并为煤层瓦斯的开采与分离提供了有用的信息.     

CH4, CO2和H2O在非金属原子修饰石墨烯表面的吸附

煤层气(矿井瓦斯)是一种有望替代传统化石燃料，如煤、石油和天然气的非常规气体. 作为可得的清洁能源，它的利用被认为是节能和经济的选择. 在本工作中，非金属原子X(X=H，O，N，S，P，Si，F，Cl)修饰的石墨烯(Gr)被用来代表具有结构异性的煤表面模型. 通过密度泛函理论系统地研究了煤层气组分Y(Y=CH₄，CO₂，H₂O)在非金属原子修饰石墨烯上的吸附作用. 结果表明Y在非金属原子修饰石墨烯上的吸附均为物理吸附. 态密度和差分电荷密度共同表明了这种弱的相互作用.其中，H和Cl对CH₄的作用较大； N、O、F、Cl对CO₂的作用较强； N，Cl对H₂O的影响不容忽视. 总的来说，吸附能大小依次为：H₂O>CO₂>CH₄. 因此，在CH₄富集的煤层里注入H₂O或CO₂可以与CH₄形成竞争吸附，进而提高煤层气采收率. 本工作提供了在分子水平下煤层气与非金属原子修饰石墨烯之间的相互作用的详情，并为煤层瓦斯的开采与分离提供了有用的信息.     

CH4, CO2和H2O在非金属原子修饰石墨烯表面的吸附

煤层气(矿井瓦斯)是一种有望替代传统化石燃料，如煤、石油和天然气的非常规气体. 作为可得的清洁能源，它的利用被认为是节能和经济的选择. 在本工作中，非金属原子X(X=H，O，N，S，P，Si，F，Cl)修饰的石墨烯(Gr)被用来代表具有结构异性的煤表面模型. 通过密度泛函理论系统地研究了煤层气组分Y(Y=CH₄，CO₂，H₂O)在非金属原子修饰石墨烯上的吸附作用. 结果表明Y在非金属原子修饰石墨烯上的吸附均为物理吸附. 态密度和差分电荷密度共同表明了这种弱的相互作用.其中，H和Cl对CH₄的作用较大； N、O、F、Cl对CO₂的作用较强； N，Cl对H₂O的影响不容忽视. 总的来说，吸附能大小依次为：H₂O>CO₂>CH₄. 因此，在CH₄富集的煤层里注入H₂O或CO₂可以与CH₄形成竞争吸附，进而提高煤层气采收率. 本工作提供了在分子水平下煤层气与非金属原子修饰石墨烯之间的相互作用的详情，并为煤层瓦斯的开采与分离提供了有用的信息.     

CH4, CO2和H2O在非金属原子修饰石墨烯表面的吸附

煤层气(矿井瓦斯)是一种有望替代传统化石燃料，如煤、石油和天然气的非常规气体. 作为可得的清洁能源，它的利用被认为是节能和经济的选择. 在本工作中，非金属原子X(X=H，O，N，S，P，Si，F，Cl)修饰的石墨烯(Gr)被用来代表具有结构异性的煤表面模型. 通过密度泛函理论系统地研究了煤层气组分Y(Y=CH₄，CO₂，H₂O)在非金属原子修饰石墨烯上的吸附作用. 结果表明Y在非金属原子修饰石墨烯上的吸附均为物理吸附. 态密度和差分电荷密度共同表明了这种弱的相互作用.其中，H和Cl对CH₄的作用较大； N、O、F、Cl对CO₂的作用较强； N，Cl对H₂O的影响不容忽视. 总的来说，吸附能大小依次为：H₂O>CO₂>CH₄. 因此，在CH₄富集的煤层里注入H₂O或CO₂可以与CH₄形成竞争吸附，进而提高煤层气采收率. 本工作提供了在分子水平下煤层气与非金属原子修饰石墨烯之间的相互作用的详情，并为煤层瓦斯的开采与分离提供了有用的信息.     

CH4, CO2和H2O在非金属原子修饰石墨烯表面的吸附

煤层气(矿井瓦斯)是一种有望替代传统化石燃料,如煤、石油和天然气的非常规气体. 作为可得的清洁能源,它的利用被认为是节能和经济的选择. 在本工作中,非金属原子X(X=H,O,N,S,P,Si,F,Cl)修饰的石墨烯(Gr)被用来代表具有结构异性的煤表面模型. 通过密度泛函理论系统地研究了煤层气组分Y(Y=CH₄,CO₂,H₂O)在非金属原子修饰石墨烯上的吸附作用. 结果表明Y在非金属原子修饰石墨烯上的吸附均为物理吸附. 态密度和差分电荷密度共同表明了这种弱的相互作用.其中,H和Cl对CH₄的作用较大; N、O、F、Cl对CO₂的作用较强; N,Cl对H₂O的影响不容忽视. 总的来说,吸附能大小依次为：H₂O>CO₂>CH₄. 因此,在CH₄富集的煤层里注入H₂O或CO₂可以与CH₄形成竞争吸附,进而提高煤层气采收率. 本工作提供了在分子水平下煤层气与非金属原子修饰石墨烯之间的相互作用的详情,并为煤层瓦斯的开采与分离提供了有用的信息.