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.     

X油藏注气混相驱可行性实验研究

针对X底水油藏油井注水后综合含水上升过快的问题,利用HB70/300型高压物性分析仪开展了该区块原油相态特征实验、注气相态特征实验,并运用细管法开展了注CO₂最小混相压力实验。对比分析了CO₂和N₂两种性质气体注入前后原油的相态特征变化,确定了该区块原油注CO₂最小混相压力,为X油藏注气提高采收率可行性提出依据。实验结果表明,X油藏原始地层压力为46.01 MPa,原油饱和压力为11.06 MPa,注N₂后饱和压力上升迅速,在原始地层条件下难以实现混相,表现出典型的非混相特征;注CO₂后饱和压力上升较平缓,细管法测得的最小混相压力为28.03 MPa,说明利用CO₂可实现CO₂的混相驱替,而且最终的驱替效果比较理想。说明该油藏可开展注CO₂混相驱,为进一步的开发方案调整提供了依据和合理的建议。      

Visualization of CO2 and oil immiscible and miscible fl ow processes in porous media using NMR micro-imaging

CO₂ flooding is considered not only one of the most effective enhanced oil recovery（EOR） methods,but also an important alternative for geological CO₂ storage.In this paper,the visualization of CO₂ flooding was studied using a 400 MHz NMR micro-imaging system.For gaseous CO₂ immiscible displacement,it was found that CO₂ channeling or fingering occurred due to the difference of fluid viscosity and density.Thus,the sweep efficiency was small and the final residual oil saturation was 53.1%.For supercritical CO₂ miscible displacement,the results showed that piston-like displacement occurred,viscous fingering and the gravity override caused by the low viscosity and density of the gas was effectively restrained,and the velocity of CO₂ front was uniform.The sweep efficiency was so high that the final residual oil saturation was 33.9%,which indicated CO₂ miscible displacement could enhance oil recovery more than CO₂ immiscible displacement.In addition,the average velocity of CO₂ front was evaluated through analyzing the oil saturation prof ile.A special core analysis method has been applied to in-situ oil saturation data to directly evaluate the local Darcy phase velocities and capillary dispersion rate.     

Effects of hydrocarbon solvents on simultaneous improvement in displacement and sweep efficiencies during CO2-enhanced oil recovery

The addition of hydrocarbon solvent such as liquefied petroleum gas (LPG) to the CO₂ stream leads to miscible conditions in reservoirs at lower pressures by reducing the minimum miscibility pressure (MMP). Under miscible conditions, improved displacement and vertical sweepout occur simultaneously. The influences of LPG concentration and composition on the displacement and sweep efficiencies during CO₂-LPG enhanced oil recovery (EOR) were investigated. Enhanced displacement efficiency was assessed through oil viscosity reduction and oil saturation change. Moreover, the miscible flooding induced by LPG addition, which resulted in increased solvent viscosity and a lower density difference between the injected fluid and reservoir oil, provided a smaller viscous gravity number, and improved the sweep efficiency, alleviating the impact of solvent gravity override. For CO₂-LPG EOR, oil recovery increased up to 52% as compared with that for CO₂ flooding. The amount of incremental oil recovery with 100% butane in the LPG was 16%, as compared with the 100% propane case. Mitigated gravity override enabled CO₂-LPG EOR to enhance sweep efficiency. Results indicated that the compositional modeling of the EOR process with the addition of LPG provided more accurate prediction on the performance of CO₂-LPG EOR.     

Evaluation of miscible and immiscible CO2 injection in one of the Iranian oil fields

Carbon dioxide (CO₂) flooding is one of the most important methods for enhanced oil recovery (EOR) because it not only increases oil recovery efficiency but also causes a reduction of greenhouse gas emissions. It is a very complex system, involving phase behavior that could increase the recovery of oil by means of swelling, evaporation and decreasing viscosity of the oil. In this study, a reservoir modeling approach was used to evaluate immiscible and miscible CO₂ flooding in a fractured oil field. To reduce simulation time, we grouped fluid components into 10 pseudo-components. The 3-parameter, Peng–Robinson Equation of State (EOS) was used to match PVT experimental data by using the PVTi software. A one-dimensional slim-tube model was defined using ECLIPSE 300 software to determine the minimum miscibility pressure (MMP) for injection of CO₂. We used FloGrid software for making a reservoir static model and the reservoir model was calibrated using manual and assisted history matching methods. Then various scenarios of natural depletion, immiscible and miscible CO₂ injection have been simulated by ECLIPSE 300 software and then the simulation results of scenarios have been compared. Investigation of simulation results shows that the oil recovery factor in miscible CO₂ injection scenario is more than other methods.     

Simulation Study of Different Modes of Miscible Carbon Dioxide Flooding

Carbon dioxide flooding has been applied worldwide as a successful enhanced oil recovery. Carbon dioxide flooding may be applied as a continuous injection or as water-alternating-gas (WAG) process. Optimization of the injection mode of carbon dioxide is important for economical field application. This paper focuses on using a fully compositional simulation model for “AEB-3C” sandstone oil reservoir of one of the Western Desert oil fields in Egypt to predict the impact of CO₂ miscible flooding on the reservoir oil recovery and net present value (NPV), to define the best mode of operation that is straight CO₂ injection or water alternating gas (WAG) processes and to show the difference between pure and impure CO₂. Moreover, several sensitivity runs were done on the oil price to show minimum profitable value of oil price when applying such a tertiary method in the subject field.The reservoir under study has been producing under a successful water flooding project since May-2010. The recovery factor by the end of water flooding project is predicted as 32%. CO₂ flooding processes have started by the end of water flooding. A significant increase in the oil recovery factor was noticed due to applying this method; it reached up to 57%. Comparisons between different modes of operations were shown which showed better results when applying WAG process than that with straight CO₂ injection. Moreover; sensitivities were done on the cycle periods in WAG processes and showed increase in the recovery factor with shortening the cycle periods. In addition to a comparison between pure and impure CO₂ which showed very close results.     

浅层油藏稠油热水/CO2驱油效率实验模拟研究

新疆油田九_6区齐古组浅层稠油油藏已进入蒸汽开采中后期,油藏开采经历了蒸汽吞吐、加密调整、蒸汽驱过程,采出程度为37%。现阶段单一蒸汽驱效果明显下降,地层亏空严重,蒸汽热利用效率低,吸汽不均,波及程度差异大,油水流度比大,采收率低。热水复合CO_2驱油充分利用热水热效应和发挥CO_2溶解降黏等作用,是提高原油采收率的有效方法。因此,针对九_6区稠油开展不同混合方式热水/CO_2驱油模拟实验,分别研究了纯热水驱、热水与CO_2混注、热水与CO_2段塞的驱油效率。结果表明,纯热水驱累积驱油效率为49.19%,热水/CO_2混注累积驱油效率最大为71.25%,段塞驱累积驱油效率高达85.96%。同时,分析了驱出原油及岩心残余油组分变化。     

A laboratory investigation of carbon dioxide-enhanced oil recovery by focusing on CO2-oil physical properties

Carbon dioxide (CO₂) miscible flooding has become an important method in enhanced oil recovery (EOR) for recovering residual oil. In addition it may help in protection of the environment as (CO₂) is widely viewed as an important agent in global warming. Knowledge of the interactions between (CO₂) and reservoir crude oil is very critical for any (CO₂)-enhanced oil recovery (EOR) projects. This paper shows the effect of (CO₂) miscible flooding application for Egyptian oil fields by swelling studies. The swelling test is a laboratory simulation of the process of injecting gradually different percentage of (CO₂) gas into a reservoir containing under-saturated oil. The gas (injection solvent) can dissolve, causing the reservoir fluid to swell. This paper presents a summary of a wide range of laboratory tests conducted on ten different crude oils varying from 26.4 to 40.5 API. These were used to invested the use of (CO₂) and its effect on parameters such as viscosity, density, gas solubility and swelling factor as a function of pressure at temperature from 620.3 to 706.0?°R.     

Modeling of Asphaltene Deposition During Miscible CO2 Flooding

The authors present the results of numerical tests and simulations to investigate and analyze the likelihood of asphaltene precipitation and deposition during CO₂ flooding in a reservoir. The effects of asphaltene precipitation on oil properties such as oil viscosity and density during miscible CO₂ flooding process were elaborated by using Winprop software of Computer Modeling Group. Also oil properties change during CO₂ miscible flooding by numerical slim tube were investigated by a compositional simulator (GEM). A fluid sample of Saskatchewan Reservoir that had been flooded miscibly with CO₂ was chosen for performing the sensitivity analyses. The results showed that asphaltene precipitation reduces the oil viscosity and density that is in favor of production increasing. On the other hand asphaltene deposition causes resistance in oil production due to porosity and permeability reduction. The competition between these two effects declares the positive or negative effect of asphaltene on recovery that could be different for each reservoir. The results also show that decreasing the rate of CO₂ injection leads to an increase in asphaltene deposition near the injective well. Due to this phenomenon in higher injecting rates the increment in well bottom-hole pressure becomes less.     

Modeling CO2 miscible flooding for enhanced oil recovery

The injection of fuel-generated CO2 into oil reservoirs will lead to two benefits in both enhanced oil recovery (EOR) and the reduction in atmospheric emission of CO2. To get an insight into CO2 miscible flooding performance in oil reservoirs, a multi-compositional non-isothermal CO2 miscible flooding mathematical model is developed. The convection and diffusion of CO2-hydrocarbon mixtures in multiphase fluids in reservoirs, mass transfer between CO2 and crude, and formation damages caused by asphaltene precipitation are fully considered in the model. The governing equations are discretized in space using the integral finite difference method. The Newton-Raphson iterative technique was used to solve the nonlinear equation systems of mass and energy conservation. A numerical simulator, in which regular grids and irregular grids are optional, was developed for predicting CO2 miscible flooding processes. Two examples of one-dimensional (1D) regular and three-dimensional (3D) rectangle and polygonal grids are designed to demonstrate the functions of the simulator. Experimental data validate the developed simulator by comparison with 1D simulation results. The applications of the simulator indicate that it is feasible for predicting CO2 flooding in oil reservoirs for EOR.     

A simulation approach in economic assessment and risk analysis of the CO2 miscible flooding process

Due to high cost and technical uncertainty of recovery processes, predictive models developed for CO₂ miscible flooding processes should be used to evaluate the production performance of projects. This study presents the reservoir simulation study and probabilistic cash flow analysis of CO₂ miscible flooding projects in West Virginia. An extended black oil reservoir simulator was used in this study. Historical data and information from a CO₂ injection pilot in Granny's Creek Field of Clay County in West Virginia were used. A history match was done, and then alterative matched cases were run, such as pure CO₂ injection and water-alternate-gas (WAG) injection. A PC-based probabilistic cash flow analysis (PCFA) model was developed to analze the economic evaluation of the CO₂ miscible flooding project on a popular spreadsheet.Statistical analysis of the results shows: (1) the WAG case is more profitable than the pure CO₂ injection case; (2) the pure CO₂ injection case and the WAG case are more economical than the base case. Therefore, given current oil prices, the CO₂ processes have a higher potential to succeed in tec technical aspects but not in economical aspects. This study initiates the adaptation of the model to specific parameters of West Virginia oil fields. The newly formulated microcomputer PCFA model overcomes some of the problems commonly found in the conventional Monte Carlo simulation. Thus, the simulation approach in economic assessment and risk analysis can be readily adopted in future projects.     

江苏油田CO2混相驱现场试验研究

对江苏油田富14断块进行的可行性研究结果表明,复杂小断块油藏可以进行经济有效的CO₂混相驱。江苏油田富14断块在保持最低混相压力的状态下,于1998年末开始进行了CO₂—水交替(WAG)的注入试验。进行了6周期的注入试验后,水气比由0.86:1升至2:1。油井见到了明显的增油降水效果,水驱后油层中形成了新的含油富集带。试验区采油速度由0.5%升至1.2%,综合含水率由93.5%降至63.4%。到目前为止,CO₂波及区采收率已提高4%,CO₂利用率为1240m³/t(油)。试验仍在继续进行。富14断块CO₂混相驱的成功为提高复杂小断块油藏采收率和丰富国内三次采油技术提供了重要的依据。     

注CO_2混相驱油藏合理采收率确定

为确定CO2混相驱油藏合理采收率,基于水驱油分流量方程、Buckley-Leverett水驱油非活塞理论及CO2混相驱特性(即混相驱油藏不存在界面张力,各相渗透率与对应相饱和度成正比),将水驱油分流量方程进行适当改进,其物理性影响因素更加明显,更适用于CO2混相驱油藏,并推导出CO2气体分流系数关系式和原油采出程度与累积注气量之间的关系式,用来设计和预测CO2混相驱开发参数。同时对采出程度与累计注气量之间的数学关系式求导,得到了注CO2混相驱油藏合理采收率导数方程的数学模型,可为计算合理注入CO2量及注CO2混相驱最终采收率提供参考。     

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.     

An Experimental Study on the Applicability of Water-alternating-CO2 Injection in the Secondary and Tertiary Recovery in One Iranian Reservoir

Abstract

The objective of this study was to experimentally investigate the performance of water-alternating gas (WAG) injection in one of Iran's oil reservoirs that encountered a severe pressure drop in recent years. Because one of the most appropriate studies to evaluate the reservoir occurs generally on rock cores taken from the reservoir, core samples drilled out of the reservoir's rock matrix were used for alternating injection of water and gas. In the experiments, the fluid system consisted of reservoir dead oil, live oil, CO₂, and synthetic brine; the porous media were a number of carbonate cores chosen from the oilfield from which the oil samples had been taken. All coreflood experiments were conducted using live (recombined) oil at 1,700 psi and reservoir temperature of 115°F. A total of four displacement experiments were performed in the core, including two experiments on secondary WAG injection and others on the tertiary water and gas invaded zones WAG injections. Prior to each test porosity and permeability of dried cores were calculated then 100% water-saturated cores were oil-flooded to obtain connate water saturation. Therefore, all coreflooding tests started with the samples at irreducible water saturation. Parameters such as oil recovery factor, water cut, and gas-oil ratio and production pressure of the core were recorded for each test. The most similar experimental work with the main reservoir condition, indicated that approximately 64% oil were recovered after 1 pore volume of WAG process at 136,000 ppm brine salinity. Although tests show ultimate recovery of 79% and 55% for secondary and tertiary injection in gas and water invaded zones, respectively, immiscible WAG injection efficiency in the gas and water invaded zones will not be proper. In the similar test to field properties, the average pressure difference about 70 Psig was observed, which shows stable front displacement. These experiments showed that there was significant improvement in the oil recovery for alternating injection of water and CO₂, especially in the secondary recovery process. Water breakthrough time in almost all of the tests shows frontal displacement of injected fluid in cores and produced gas-oil ratio changes a little whenever the injection is miscible and increases rapidly in immiscible processes.     

The Experimental Investigation of Nitrogen and Carbon Dioxide Water-alternating-gas Injection in a Carbonate Reservoir

Abstract

Floods were conducted using rock–fluid systems consisting of carbonate cores from Binak reservoir, which is located in southwest of Iran, oil and brine. The coreflood protocol consisted of a series of steps including brine saturation, absolute permeability determination, flooding with oil to initial oil saturation, endpoint oil permeability determination, and, finally, nitrogen and carbon dioxide water-alternating-gas (WAG) injections. The effect of slug size on oil recovery was investigated using immiscible nitrogen (N₂) WAG injection and the amount of oil recovered was compared with continuous injection of N₂. Experimental results show that ultimate oil recovery is not very sensitive to changing the slug sizes for N₂ WAG injection, although the slug size of 0.15 pore volume (PV) injection is better than others. As less PV is injected, a higher oil production rate is achieved. Also, N₂ WAG flood appeared to be better in performance than continuous gas injection (CGI) of nitrogen. Carbon dioxide (CO₂) injection was performed in three modes, including CGI, WAG injection, and hybrid WAG. Experimental results show that for optimization of oil recovery in CO₂ floods, a continuous gas slug of 0.4–0.5 PV followed by 1:1 WAG needs to be injected.     

Integrated Investigation of Enhanced Oil Recovery in South Slattery Minnelusa Reservoir,Part 2: CO2 Miscible Injection

Abstract

The authors used experiment and full-field reservoir modeling to investigate and optimize the design of a CO₂ miscible flooding project for the Minnelusa reservoir of the South Slattery field. Minimum miscibility pressure and core flooding tests were conducted to estimate the CO₂ injection feasibility at Slattery conditions. A full-field CO₂ model with finely gridded patterns was built using oil saturations and pressures at the end of history in the waterflood model. The CO₂ model identified the best patterns for CO₂ flooding and was instrumental in selecting a strategy for sizing the initial flood area and in determining the size, location, and timing of future expansions of the CO₂ flood. Continuous CO₂ miscible injection (CMI) and alternating (WAG) were simulated. WAG injections were simulated mainly to observe the improvement of low sweep efficiency caused by override and unfavorable mobility ratio. The integrated recovery efficiency comparison of CMI and WAG was used to demonstrate the mobility control of the WAG process.     

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.     

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.     

特低渗砂岩油藏CO2-低界面张力黏弹流体协同驱油机理研究

目的 特低渗油藏储层物性差、层间非均质性强,造成CO₂驱易发生气窜,提高采收率效果欠佳,其中,CO₂水气交替驱作为结合CO₂驱和水驱优势的方法,具有较高的适用性。为进一步改善CO₂-水交替驱的开发效果,开展了CO₂-低界面张力黏弹流体协同驱油研究。方法 通过界面张力和润湿性能测试评价低界面张力黏弹流体基本性能,并利用微观可视化驱油实验及岩心驱油实验等,探究了不同驱替方式的驱油效果和CO₂-低界面张力黏弹流体协同驱油过程中二者之间的“协同作用”机理。结果 低界面张力黏弹流体具备良好的界面活性和改变岩石表面润湿性能力,水驱后开展CO₂驱、低界面张力黏弹流体驱、CO₂-低界面张力黏弹流体交替协同驱,采收率可在水驱基础上分别提高0.91%、10.66%、16.25%,其提高采收率机理包括降低界面张力、改善流度比、改变岩石表面润湿性及乳化作用的协同效应等。结论 CO₂-低界面张力黏弹流体协同驱既可有效...