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.     

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.     

国外CO2驱流度控制进一步扩大波及体积方法

CO₂驱油是一种有效的提高采收率方法,矿场成功应用已有60多年。理论上微观驱油效率接近100%,但相对原油,CO₂的低黏度低密度与储层的非均质性导致的黏性指进和重力分离两大典型问题大大降低了气体波及系数。本文综述了国外各种流度控制方法,包括气水交替、聚合物直接稠化CO₂、CO₂泡沫驱、气-化学剂联合方法及气体辅助重力泄油,简要介绍了CO₂驱扩大波及体积的其他方法,分析了每种方法的机理及优缺点,力图为我国CO₂驱油进一步扩大波及体积这一难题积累先进做法和经验。     

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.     

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.     

稠油降黏剂驱提高采收率机理

为系统研究降黏剂驱这一新的开发方式提高采收率机理,应用单管填砂驱油模型、三维填砂驱油模型和微观玻璃刻蚀驱油模型,测试降黏剂驱的驱油效率和波及系数,并对其原因进行分析。实验结果表明,降黏剂驱通过提高驱油效率和增加波及系数提高采收率。与水驱相比,降黏剂驱可提高驱油效率13%,其机理为:①分散乳化,形成水包油的小油滴,有利于通过狭窄的喉道,降低原油的表观黏度;②降低界面张力,增加毛管数,降低残余油饱和度。同时,降黏剂驱将波及系数由水驱时18.8%提高到39.9%,其机理为:①乳液调驱,分散乳化的原油进入水窜通道,水渗流面积减小、阻力增加,后续注入液进入以前未波及区域;②贾敏效应,降黏乳化小油滴聚并成大油滴堵在孔喉处,周围驱替液转向。研究明晰了降黏剂驱提高采收率机理,为后续开发技术界限研究及现场应用奠定基础。     

氢监测技术在含硫输气管线上的应用

采用腐蚀挂片、缓蚀剂残余浓度分析以及氢监测技术,在含硫输气管线上研究了缓蚀剂应用效果,确定了缓蚀剂的有效保护时间。结果表明,氢监测技术能够无损、实时、全周相地监测含硫输气管线腐蚀状况,缓蚀剂残余浓度分析及氢监测结果显示缓蚀剂有效保护时间达到1个月以上。     

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。     

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.     

The Areal Sweep Efficiency of the First-contact Miscible Displacements: An Experimental Approach

Abstract

Solvent flooding using the water alternating gas (WAG) technique is very important for predicting the process performance. This technique has been employed in a number of oil fields. However, little data are available in the literature. Therefore, there is an immense need for the sweep efficiency data resulting from first-contact miscible flooding, particularly in view of conducting reservoir simulation studies. In this article, we conducted a series of WAG displacements through glass bead packs. A number of miscible WAG displacement tests were conducted at WAG ratios of 1:1, 1:2, and 2:1. Constant flow rates were used to mask the effects of capillary number on sweep efficiency. Experimental results revealed that the WAG ratio affects the sweep efficiency of the miscible flooding process. In addition, new correlations of areal sweep as function of mobility ratio at various WAG ratios were developed. The data provided can be useful to the oil industry in conducting analytical and numerical modeling studies of miscible WAG processes.     

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.     

Flow Properties of CO2/Crude Oil in Miscible Phase Flooding

Abstract

The high-temperature and high-pressure three-dimensional (3D) device is used to study miscible flooding of CO₂ and crude oil. The experiment model is a real sand plate. In oil reservoir condition, there is a large difference between production and injection volume. The complex flowing characteristics of CO₂ flooding in pore media are observed in recovery, water cut, and gas–oil ratio curves. By analyzing the water saturation contour plot measured by a saturation probe, CO₂ and oil can be miscible. The viscosity of miscible liquid and flowing pressure decreases. This is the important mechanism of enhanced oil recovery. When the viscosity of miscible liquid and flowing pressure decreases, miscible CO₂ and oil contacted with water can make a similar three phase. This is the important mechanism of enhanced oil recovery. Based on the conclusion, the main reason for the production and injection difference is that high-density CO₂ would flow into pore media in which water and oil cannot flow.     

化学驱波及效率和驱替效率的影响因素研究

在对一个非均质程度严重的油藏进行波及效率和驱替效率定量描述的基础上,利用我国自行研制的ASP数值模拟软件,建立了一系列正韵律二维剖面地质模型,对比研究不同的油藏非均质性对化学驱波及效率和驱替效率的影响.在渗透率层间级差相同的情况下,高渗透层厚度与总厚度的比例不同,聚合物驱和三元复合驱的驱油效果不同;分析研究了重力作用对三元复合驱驱油效果的影响,并提出注采井距的缩小会削弱重力作用的影响.研究表明,地质模型不同,化学驱驱油效果的差异很大.对三元复合驱和聚合物驱进行油藏适应性研究,对提高水驱后采收率有着十分重要的意义.图3表2参7     

化学驱波及效率和驱替效率的影响因素研究

在对一个非均质程度严重的油藏进行波及效率和驱替效率定量描述的基础上,利用我国自行研制的ASP数值模拟软件,建立了一系列正韵律二维剖面地质模型,对比研究不同的油藏非均质性对化学驱波及效率和驱替效率的影响。在渗透率层间级差相同的情况下,高渗透层厚度与总厚度的比例不同,聚合物驱和三元复合驱的驱油效果不同;分析研究了重力作用对三元复合驱驱油效果的影响,并提出注采井距的缩小会削弱重力作用的影响。研究表明,地质模型不同,化学驱驱油效果的差异很大。对三元复合驱和聚合物驱进行油藏适应性研究,对提高水驱后采收率有着十分重要的意义。图3表2参7     

Compositional modeling and simulation of dimethyl ether (DME)- enhanced waterflood to investigate oil mobility improvement

Dimethyl ether (DME) is a widely used industrial compound, and Shell developed a chemical EOR technique called DME-enhanced waterflood (DEW). DME is applied as a miscible solvent for EOR application to enhance the performance of conventional waterflood. When DME is injected into the reservoir and contacts the oil, the first-contact miscibility process occurs, which leads to oil swelling and viscosity reduction. The reduction in oil density and viscosity improves oil mobility and reduces residual oil saturation, enhancing oil production. A numerical study based on compositional simulation has been developed to describe the phase behavior in the DEW model. An accurate compositional model is imperative because DME has a unique advantage of solubility in both oil and water. For DEW, oil recovery increased by 34% and 12% compared to conventional waterflood and CO₂ flood, respectively. Compositional modeling and simulation of the DEW process indicated the unique solubility effect of DME on EOR performance.     

特高含水后期提高采收率物理模拟实验

为了探索特高含水后期剩余油的潜力区和不同驱油方法提高采收率的机理,采用三维大模型物理模拟实验,研究了高倍数水驱、活性剂驱、聚合物驱、二元复合驱、微球-乳化剂驱过程中注入压力、波及系数的变化情况和剩余油饱和度的分布特征。研究结果表明,特高含水后期提高采收率的潜力区为未波及区的剩余油和已波及的弱水洗区和中水洗区,而不是强水洗区;继续高倍数水驱和超低界面张力活性剂驱不能进一步扩大波及系数,提高采收率潜力小,需采用深部调堵+微调驱油相结合的技术。自聚集微球-乳化剂驱具有封堵-驱替-再封堵-再驱替的特点,可扩大波及系数38.6%,提高采收率19.1%,其封堵能力、波及范围和驱油效率均明显高于聚合物驱和二元复合驱,具有良好的应用前景。     

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。      

沙一下油藏CO2混相驱替提高采收率的研究

以沙一下区块油藏为对象,研究了CO2混相驱技术可行性及提高采收率,通过PVT实验和细管模拟实验,确定了油藏原油的最小混相压力为18.41 MPa,原油采收率达90.01%。实验结果表明,注气驱达到混相压力后,注入压力对驱油效率影响不大,而在混相压力以下的近混相区,注入压力对驱油效率影响非常大。通过长岩心驱替模拟实验,对比了水驱和CO2驱替效率,结果表明CO2混相驱提高采收率达40.8%。     

聚合物驱后提高采收率方法室内实验研究

利用三维大型物理模型进行了聚合物驱油实验,研究了非均质砂岩油田聚合物驱油过程中波及系数变化情况和聚合物驱后剩余油分布特征。对4种不同方法的驱油实验对比研究结果表明,在聚合物驱后,高渗层位的波及系数较大,进一步扩大波及体积而降低剩余油饱和度的潜能较小,可通过二元或三元体系驱方式提高驱油效率来进一步挖潜剩余油;而中、低渗透层的波及系数低,含油饱和度高,可采用调剖或高黏度聚合物驱扩大波及体积与三元复合驱提高驱油效率相结合的方法进一步提高最终采收率。     

胜利油田高89区块低渗油藏CO2近混相驱替机理研究

低渗透油藏中CO2驱较难实现混相,而非混相驱驱替效率较低。为实现高效率非混相驱油,以胜利油田高89区块油藏为对象,研究了CO2近混相驱技术可行性及提高采收率机理。通过PVT实验和细管实验,确定了油藏原油的最小混相压力;通过不同相态下的岩心驱替实验,研究了相态变化对CO2驱替效率的影响;通过油藏数值模拟分析了CO2近混相驱提高采收率的机理。实验结果表明,近混相驱与混相驱相似,同样具有溶解、抽提等作用,对于较难实现混相驱的低渗透油藏,近混相驱同样可以达到较好的开发效果。