模拟延长油田CO_2驱油过程原油结蜡特性研究

通过对某CO2驱油区块的不同CO2分压条件下原油结蜡倾向和原油结蜡特性评价,计算出原油的结蜡速率、结蜡率及蜡含量,分析了原油的析蜡曲线特性。结果表明,CO2分压增大时原油的结蜡速率和结蜡率提高,蜡含量降低,蜡析出更明显;经CO2处理作用后原油析蜡点向低温方向移动,其蜡含量也相应地比未处理油样的蜡含量降低。     

Changes in the properties of conventional crude oil before and after CO2 flooding

Abstract

In order to enhance oil recovery of a conventional oil reservoir by CO₂ flooding, the changes in the properties of the crude oil before and after CO₂ flooding are systematically investigated by on-site sampling and experimental testing. The results show that, after CO₂ flooding, the light hydrocarbons of the produced crude oil is increased and the heavy hydrocarbons of the produced crude oil is decreased due to the deposition of resins and asphaltenes in the pores of the formation. In addition, the produced fluid (a mixture of oil and water) has a high water separation rate, the oil- water interface has a high tension value, and the crude oil has a high acid value and a low viscosity. The conclusions can provide a certain guidance for high-efficiency development of a conventional oil reservoir by CO₂ flooding.     

CO2 miscible flooding in low permeability sandstone reservoirs and its influence on crude oil properties

Miscible CO₂ injection process has become widely used technique for the enhanced oil recovery in low permeability reservoirs. Core flooding experiments and field test of CO₂ miscible flooding in low permeability sandstone reservoirs and its influence on crude oil properties was studied. The results showed that CO₂ miscible flooding in low permeability sandstone reservoirs can enhance oil recovery both in laboratory study and field test. The permeability of sandstone reservoirs decreased during CO₂ miscible flooding due to the precipitation of asphaltene of crude oil. The precipitation of asphaltene lead to a reduction of asphaltene content and the apparent viscosity of crude oil. A further study on inhibitors and removers for asphaltene deposits from crude oil should be investigated to prevent and remove asphaltene deposits in low permeability sandstone reservoirs.     

Influence of pressure and CO2 content on the asphaltene precipitation and oil recovery during CO2 flooding

During CO₂ flooding, the crude oil is treated with CO₂, and meanwhile it is displaced by CO₂. Based on the two processes, the influence of pressure and CO₂ content on the asphaltene precipitation and oil recovery efficiency are systematically investigated by indoor simulation experiment. With the increase of the pressure or CO₂ content during CO₂ treatment, the amount of asphaltene precipitation can be increased to a certain value. Correspondingly, the degrees of the changes of oil-water interface, the compositions of crude oil, and reservoir permeability are positively correlated with the amount of asphaltene precipitation. However, during the process, the oil recovery has an optimal value due to the combined action of asphaltene precipitation and the improvement of flow performance of the crude oil. These conclusions can provide a basis for high efficiency development of low permeability oil reservoirs by CO₂ flooding.     

The effect of dynamic cooling on the flow properties of PPD-treated crude oil

Abstract

By means of DSC, test of flow parameters, and microscopic observation, this paper studied the relation between the influence on the low temperature flow properties and that on the waxy crystal of the PPD-treated crude oil due to different final temperature of dynamic cooling. It has been experimental confirmed that the influence caused by the final temperature of dynamic cooling on low temperature flow properties and waxy crystal vary from the different final temperature of dynamic cooling. With this temperature increases, the depressive effects first get worse, then improved and finally kept nearly unchanged at higher temperature.     

Influence of injection pressure and injection volume of CO2 on asphaltene deposition

To further improve the oil displacement effect by CO₂ flooding, the trends and conditions of asphaltene deposition under different injection pressures and injection volumes of CO₂ were studied by SDS solid phase deposition testing system, high temperature and high pressure microscope, and P-X phase diagram. When the mole fraction of CO₂ in crude oil increases to a certain value, asphaltene deposition appears. The lower the pressure, the lower the mole fraction of CO₂ in crude oil causing the asphaltene deposition there is. After the onset of asphaltene deposition, the degree of deposition increases with an increase in pressure. The amount of the deposited asphaltene under miscible displacement is the highest, under near-miscible displacement is the second highest, and under immiscible displacement is the lowest. When the dissolution of CO₂ in crude oil reaches the saturation point, the asphaltene deposition becomes slow. Besides, it is feasible to prevent or reduce the asphaltene deposition by adjusting the thermodynamic parameters according to the phase behaviors of the CO₂-crude oil system. The experimental results can provide theoretical basis for optimization design of the parameters of CO₂ flooding.     

Investigation of immiscible CO2 and C1 injection and comparison with water injection for enhanced oil recovery in naturally fractured reservoirs

Reservoir oil and gas content tends to rise up to the surface as long as their potential energy levels are sufficient. In order to amplify this energy, either during the time when oil is uprising on its inherent energy or since after, so as to facilitate the traveling of oil to the surface, enhanced oil recovery (EOR) methods come into play. Furthermore, the increasing demand for oil from one hand, and the shrinkage of producible reserves on the other hand, have made it unavoidable to undertake EOR techniques. Built in this research was a 10-element model of reservoir fluid to simulate its behavior. Furthermore, slim tube simulation was undertaken to determine minimum miscibility pressure for various gases. Then, different scenarios of natural depletion, CO₂ injection, methane injection, and water injection were simulated by ECLIPSE 300 software package with the results of different scenarios compared. The results indicated water injection to be associated with higher recovery factor.     

高温高压条件下CO2 / 原油和N2 / 原油的界面张力

在油藏温度下,采用ADSA（axisymmetric drop shape analysis）技术测定了不同压力下CO₂/原油和N₂/原油体系的平衡界面张力。实验发现,原油与超临界CO₂接触的初始阶段存在强烈的扩散作用,原油中的轻质组分被超临界CO₂溶解抽提,并且随着压力的增加,这种溶解抽提作用增强;原油与N₂接触时,也存在相互扩散作用,但在本实验所测试的压力范围内（小于36 MPa）并不明显。两种体系的平衡界面张力随着压力的升高逐渐降低,其中CO₂/原油体系的平衡界面张力降低的幅度明显大于N₂/原油体系;N₂/原油体系的平衡界面张力随压力基本呈线性变化。在CO₂/原油体系中,当压力低于17.7MPa时,平衡界面张力下降非常快;当压力大于17. MPa时,CO₂/原油体系的平衡界面张力下降较慢。     

Change of the chemical and physical properties of heavy oil before and after CO2 treatment

In order to improve the heavy oil displacement effect by CO₂ flooding, the change of the chemical and physical properties of heavy oil before and after CO₂ treatment is systematically investigated by indoor simulation experiment. Experimental results show that CO₂ treatment can decrease the amount of the saturates but increase that of the aromatics, and yet has little impact on those of resins and asphaltenes. Besides, the corresponding consequence is that there has an increase in the viscosity of the heavy oil and the particle size of the asphaltene micelle, and a decrease in the conductivity of the heavy oil and n-heptane systems and the stability of the asphaltene micelle after CO₂ treatment. The conclusions can provide a certain guidance for high-efficiency development of heavy oil reservoir by CO₂ flooding.     

The effect of cationic surfactant additives on flow properties of crude oil

Pretreatment of the crude oil with flow improver or pour point depressants has received the greatest acceptance due to its simplicity and economy. Three cationic surfactants Bola form based on urea were prepared by quaternization reaction with alkyl dihalides of different chain length (hexayl, decyl-, and dodecyl-dibromide). The prepared compounds (U6, U10, and U12) were evaluated as surface active agents as well as pour point depressant for crude oil compared to monosurfactant (U12a) corresponding to (U12). The surface parameters of each synthesized surfactant were calculated from their surface tension profile including the critical micelle concentration, maximum surface excess (Γ_max), and the minimum surface area (A_min). The free energies of micellization (ΔG°_mic) and adsorption (ΔG°_ads) were also calculated. Its pour point and viscosity decreased significantly after adding surfactants. FTIR studies of crude-surfactant mixture showed remarkable decrease in concentration of viscosity enhancing groups such as alkanes, alcoholic, and acidic groups, indicating the effectiveness of both the surfactants.     

The Effects of Miscible CO2 Injection on Oil Biomarker Parameters

The purpose of this research was to study the effect of CO₂ injection on the geochemistry of crude oil in order to determine the probability of using geochemical parameters for monitoring CO₂ injection. In this process, four oil samples from different offshore oil fields were collected, synthetic steady state oil reservoir (porous media) were made by slim tube apparatus, then CO₂ injection process was done in different pressures. Various geochemical analyses were also carried out on the injected oil before and after the injection. The results show that the bulky changes on oil sample by CO₂ injection. CO₂ injection is more likely to precipitate complex and large molecules such as asphaltenes-resins and also large normal alkanes. In this case, the percentage of aromatic molecules was increased during injection. In general view on chromatograms, the height and abundance of all saturated compound peaks after CO₂ injection were significantly decreased. However, biomarker analysis shows that CO₂ injection has a tendency to change source and maturity biomarker parameters.     

Modeling crude oil gasification

Abstract

The characteristics of CO₂-gasification of crude oil under steady-state condition were studied using a simulator. The model was developed using the minimization Gibbs free energy minimization. The effects of reactor temperature and CO₂/crude oil ratio on gas composition and lower heating value (LHV) of the produced syngas were investigated. As a result, the maximum LHV was obtained at a CO₂/crude oil ratio of 0.1 and gasification temperature of 800?°C.     

注CO2过程中含沥青质原油渗流规律数值模拟研究

为进一步了解注CO2过程中含沥青质原油在油藏中的渗流规律及其对生产动态的影响，在前人研究的基础上，综合考虑沥青质的沉积、吸附及堵塞和含沥青质原油在低压力梯度时的非牛顿特性，建立了注CO2过程中含沥青质原油组分模型。为检验该模型的准确性，对一组长岩心实验数据进行数值模拟对比研究，结果表明，与常规组分模型相比，该模型模拟结果与实验数据更接近；建立单注单采模型研究注CO2对生产动态的影响，结果表明沥青质沉积吸附降低了原油采收率、沥青质沉积吸附推迟了生产井气体突破时间、含沥青质原油的流变性对原油产量的影响主要表现在气体注入初期，因此，注CO2过程中沥青质的沉积吸附及其流变性对原油产量的影响不应被忽视。图4表3参30     

An Investigation of Asphaltene Precipitation During Natural Production and the CO2 Injection Process

Some of Iranian oil reservoirs suffer from operational problems due to asphaltene precipitation during natural depletion, so widely investigation on asphaltene precipitation is necessary for these reservoirs. In this study, a reservoir that is candidate for CO₂ gas injection process is selected to investigate asphaltene precipitation with and without CO₂ injection. In this case, asphaltene precipitation is monitored at various pressures and reservoir temperature. Then, a series of experiments are carried out to evaluate the amount of precipitated asphaltene by injection different molar concentrations (25%, 50%, and 75%) of CO₂. The results show that during primary depletion the amount of precipitated asphaltene increases with pressure reduction until bubble point pressure. Below the bubble point the process is reversed (i.e., the amount of precipitated asphaltene at bubble point pressure is maximum). The behavior of asphaltene precipitation versus pressure for different concentrations of CO₂ is similar to primary depletion. Asphaltene precipitation increases with CO₂ concentration at each pressure step. In the modeling part, solid model and Peng-Robinson equation of state are employed which show a good match with experimental results.     

The Evaluation of Variable-Injection Rate Waterflooding,Immiscible CO2 Flooding,and Water-alternating-CO2 Injection for Heavy Oil Recovery

Abstract

Despite the existence of studies for separate evaluation of waterflooding, immiscible CO₂ flooding, and CO₂ water-alternating gas (WAG) for heavy oil recovery, there is a lack of an experimental, comparative evaluation of these three methods. The authors conducted tests for comparative evaluation of variable-injection rate waterflood (VIWF), immiscible CO₂ flood, and CO₂ WAG. The results illustrate the (a) effectiveness of VIWF, immiscible CO₂ flood, and CO₂ WAG; (b) effect of permeability and oil viscosity on VIWF, immiscible CO₂ flood, and CO₂ WAG; (c) effect of injection rate on VIWF; and (d) effect of slug ratio on CO₂ WAG.     

The Impact of Pore Pressure on CO2-Methane Displacement

Abstract

The intricate behavior of carbon dioxide at supercritical conditions is considered to influence the ultimate recovery of additional hydrocarbon reserves through the application of CO₂-enhanced gas recovery projects. Mixing in such a system is a diffusion-like process, which definitely depends on the physical properties of the displacing and displaced phases and the heterogeneity of the medium. The authors' aim was to experimentally investigate the consequence of pore pressure on the recovery efficiency and multiphase gas flow in a reservoirs porous medium. The displacement tests were carried out at five different pore pressures ranging from 10.34 to 40.68 MPa, temperature of 433.15 K, and displacement rate of 10 cm/hr. Results determined that improved recovery by approximately 40% can be obtained by applying the highest pore pressure in comparison with the test conducted at low pore pressure.     

Oil recovery and CO2 storage in CO2 flooding

In this study, the interfacial tension (IFT) of crude oil-carbon dioxide mixtures was measured to determine the minimum miscibility pressure. CO₂ flooding with sand packs, long cores, and heterogeneous cores was conducted to investigate the oil recovery and storage efficiency. The experiment results show that the interfacial tension decreases linearly with increasing pressure at two different pressure ranges. Under immiscible condition, the oil recovery and storage efficiency are increased by 30.1% and 52.4% when the injection pressure is increased from 13 to 22 MPa, and improved by 16.3% and 22.04% when the permeability is decreased from 270 to 10 mD, respectively. Under miscible condition, increase of injection pressure can only lead to much slower increase of oil recovery and storage efficiency, and permeability almost has no influence on oil recovery and storage efficiency. The oil recovery and storage efficiency can be remarkably reduced by heterogeneity. Water alternating CO₂ injection can improve the oil recovery and storage efficiency by 35.5% and 13.55%, respectively, compared with continuous injection.     

Operation Parameters on CO2-Foam process

Abstract

Reducing the mobility of CO₂ by means of generating in situ foam is an effective method for improving the oil recovery in CO₂ flooding processes. Implementation of the CO₂-foam technique typically involves the co-injection of CO₂ and surfactant solution into the porous medium. The surfactant molecules form bubble films that trap the flowing CO₂ molecules. The effectiveness of the CO₂-foam process is measured in terms of foam mobility. The mobility of CO₂-foam is affected by different operation parameters, such as pressure, temperature, foam quality, and brine concentration. However, surfactant type governs the overall efficiency of the CO₂-foam process. This paper presents the results of a series of experiments conducted to study the effect of various parameters on the CO₂-foam process. Bottle tests were conducted for four commercially available surfactants and among them, Chaser CD-1045 was found to be the most effective surfactant for CO₂-foam flow under reservoir conditions. It was observed that an increase in pressure from 1, 200 psi to 1, 500 psi leads to increase of the mobility of CO₂-foam, and an increase in temperature from 72 to 122°F reduces the mobility. Also, as the foam quality increases from 20 to 80%, the mobility decreases. It was observed that there was no significant effect on the mobility with an increase in brine concentration from 1 to 3 wt%.     

Evaluations of the effect of selected wax inhibitive chemicals on wax deposition in crude oil flow in sub-sea pipe-lines

Comparative studies were made on the effect of different wax inhibitive chemicals on the wax deposition volume during crude oils flow in pipeline. Two crude oils from Ovhor and Jisike oil fields in the southern part of Nigeria were used in the study. The four identified chemicals: Alkyl sulphonates (wax dispersant), polyethylene (wax inhibitors/crystal modifier), acrylate ester copolymer (pour point depressant, PPD) and xylene (wax solvents) inhibit wax deposition to varying degree of between 14.6–44.9% for crude oil A, and between 21.6–41.4% for crude oil B when 1500 ppm of each chemical was mixed with the crude oil sample. The optimal wax inhibition formulation of polyethylene, xylene, acrylate ester polymer and alkyl sulphonate contains 40.4, 19.2, 27.6, 12.8% and 36.3, 21.5, 25.8, 16.4% for crude oil A and B respectively. Applications of the optimal formulated mixtures of the above chemicals inhibit wax deposition by 58.9% and 62.4% for crude oil A and B respectively.     

CO2多次抽提作用对地层油析蜡温度影响的实验研究

利用SDS固相沉淀测试系统,针对胜利大芦湖油田樊124断块地层原油特性,研究了CO2混相驱条件下,CO2的多次抽提对地层油组分和析蜡温度的影响.研究表明:CO2对地层油中的轻烃具有很强的抽提作用,经CO2多次抽提后,地层油的析蜡温度大幅度升高,甚至超过地层温度,说明在CO2混相驱后期,会在樊124地层油中产生石蜡沉淀,因此,在矿场实施时需采取有效预防措施.