Emulsion particle size in porous media and its effect on the displacement efficiency

The emulsification process in reservoirs was simulated using core displacement experiments. Emulsions with different particle sizes were prepared using different permeability cores, and the different emulsion particle sizes formed using different permeability cores were studied. The emulsion particle size was graded against the core throat diameter, and the displacement efficiency of the different particle size emulsions was studied. The displacement mechanism of the emulsion was analyzed. The results indicated that the emulsion is mostly pore-throat scale formed in the porous media, with a particle size distribution similar to that of the core throat diameter, and the emulsion particle size increases with the increase of core permeability. The recovery percentage of emulsion flooding is greater when the matching ability of the emulsion was favorable, it is 17.07% when the matching factor is 1.08. The pore-throat scale emulsion can block high permeability zones and expand sweep volume. Moreover, due to deformation of the emulsion, the elastic stress can make the residual oil migrate forward and improve the efficiency of oil displacement.     

Foam Flooding with Ultra-Low Interfacial Tension to Enhance Heavy Oil Recovery

Severe viscous fingering during water flooding of heavy oil leaves a large amount of oil untouched in the reservoir. Improving sweep efficiency is vital for increasing heavy oil recovery. Previous researches have proved that foam flooding can increase the sweep efficiency and oil recovery. The polymers could make the foam more stable and have better plugging capacity, but the interfacial tension (IFT) of oil and water increase which could decrease the displacement efficiency of the heavy oil. In view of the deficiency of conventional foam flooding, it is necessary to research the ultra-low interfacial tension foam which could improve macro-swept volume and micro-displacement efficiency in heavy oil reservoir. In this paper a novel foam agent is developed by the combination of surfactant and additives to lower the IFT of oil and water. The operating parameters including foam injections modes and gas liquid ratio were investigated by core flooding experiments. Field test performance shows that oil production per day increased from 85.6 to 125.7 t, water cut declined from 92.1 to 83.6% after 3 months injection. This study provides a novel method to improve heavy oil recovery with an ultra-low interfacial tension foam flooding system.     

Experimental Validation of the Temperature-Resistant and Salt-Tolerant Xanthan Enhanced Foam for Enhancing Oil Recovery

Xanthan enhanced foam (XGF) is a newly developed chemical agent for enhanced oil recovery in high-temperature and high-salinity reservoirs. In this paper, laboratory experiments were performed to characterize the morphology and foam properties of XGF, to study its performance under different temperature and different salinity conditions, respectively. Based on simulate reservoir formation conditions of Xidaliya field, a series of research on XGF were conducted. The experimental results showed that the scanning electron microscopy of XGF reflected a more viscoelastic and stable nature of the foam system. High temperature had a great adverse impact upon the stability of XGF, and the increase of salinity in the solution helped to improve the stability of foam. The foam stability increased remarkably when XG4 is added, and an increase in ambient pressure made enhancement of foam stability became more noticeable. In the presence of crude oil, Xanthan could enhance the stability of emulsions and was more favorable to stabilize foam. XG4 enhanced foam had dramatic properties for mobility controlling and oil displacement in the porous media.     

中低渗透高温高盐油藏驱油共聚物P(AM/AMPSNa/AANa)的合成及性能

在中低渗透高温高盐油藏聚合物驱技术中, 超高相对分子质量聚丙烯酰胺(HPAM)存在不易注入、剪切降粘显著和耐温抗盐性能差等问题。 本文以丙烯酰胺(AM)和2-丙烯酰胺基-2-甲基丙磺酸(AMPS)为单体, 采用过硫酸胺(NH₄)₂S₂O₈和甲基丙烯酸N, N-二甲氨基乙酯(DMAEMA)作为支化结构复合引发体系, 通过共聚后水解工艺, 合成含支化结构耐温抗盐驱油共聚物P(AM/AMPSNa/AANa)。 研究了引发温度、链转移剂用量、引发剂用量对共聚物特性黏数的影响, 并通过红外光谱(IR)和¹³C NMR表征了产物结构。 筛选特性黏数1915 mL/g左右的共聚物, 进行性能评价。 实验结果表明, 共聚物具有优异的耐温抗盐性能、抗剪切性能、抗老化性、注入性和驱油性能, 可应用在中低渗透高温高盐油藏三次采油中。     

Improvement of Sweep Efficiency by Alkaline Flooding for Heavy Oil Reservoirs

Severe viscous fingering during water flooding of heavy oil leaves a large amount of oil untouched in the reservoir. Improving sweep efficiency is vital for enhancing heavy oil recovery. This study presented a laboratory study for improving sweep efficiency by alkaline flooding in heavy oil Reservoirs. This included glass-etched micromodel flooding tests, one-dimensional flooding experiments and three-dimensional physical model study. The micromodel tests show that W/O droplet flow plays a prominent role in the alkaline flooding to improve sweep efficiency. There is a minimum alkaline concentration that generates the W/O droplet flow, and the W/O droplet flow is more obvious with the alkaline concentration increasing. A series of flood tests were conducted using 325 mPa · s, 2000 mPa · s, and 3950 mPa · s heavy oils to assess the effectiveness of W/O droplet flow in alkaline flooding for enhanced heavy oil recovery. The flood tests results demonstrate the considerable potential for improved heavy oil recovery by alkaline flooding, and moreover, the incremental oil recovery has been found to increase as the alkaline concentration increases. The result obtained in three-dimensional physical model study indicates that the sweep area can be greatly improved by the formation of W/O droplet flow in alkaline flooding.     

Graded regulation technology for enhanced oil recovery and water shutoff in pore-cavity-fracture carbonate reservoirs

Although a single type of chemical agent (eg, gels, microspheres, surfactants, etc.) has achieved some effects in enhanced oil recovery of carbonate reservoirs, for pore-cavity-fracture carbonate reservoirs, the use of a single type of chemical agent does not perform well. The main objective of this study is to study the effect of different types of chemical agents in enhanced oil recovery of complex carbonate reservoirs. In order to determine the screening principle of chemical agents, the types of water channeling in the North Troyes reservoir were analyzed. For complex fractures, step by step plugging, multi-agent and multi-slug comprehensive intervention is carried out to ensure the plugging of high-permeability channels and inhibit the seepage of large channels. It can plug channeling fracture channel, adjust secondary dominant channel and reduce matrix flow resistance, so as to expand macroscopic swept volume and improve microscopic water flooding efficiency. The results show that it is difficult to comprehensively control water channeling in pore-cave-fracture carbonate reservoir, and the reservoir heterogeneity in the test area can be improved by mixing different types of control and flooding agents and carrying out deep profile control. The plugging rate of gel is 97.18 %, and the oil–water selection ratio is 0.45 in fractured core; the expansion rate of nano - microspheres is more than 3 times; the wetting modifier can improve the imbibition oil displacement efficiency by 14.76%, and the test result shown that nano - microspheres and wetting modifier have good synergistic oil displacement effect. The field application result shown that daily oil production of oil well in the test area increased by 5.0 m³/d and the daily water rate decreased by 19.0% compared with that before the control flooding. The findings of this study can help for better understanding of enhanced oil recovery in pore-cave-fracture carbonate reservoir.     

Synthesis,Characterization, and Property Evaluation of a Hydrophobically Modified Polyacrylamide as Enhanced Oil Recovery Chemical

A novel hydrophobically modified polyacrylamide p(AM/NaA/OP-10-AC/BOAM) was successfully synthesized via an aqueous micellar copolymerization method from acrylamide (AM), sodium acrylate (NaA), octylphenol polyoxyethylene acrylate (OP-10-AC), and small amounts of N-benzyl-N-octylacrylamide (BOAM), with the aim of investigating the copolymer's rheological behaviors under various conditions such as polymer concentration, shearing, temperature, and salinity. The copolymer was characterized by infrared spectroscopy, scanning electron microscopy, and atomic force microscope. Scanning electron micrographs show large aggregates in solution formed by the association from the hydrophobic groups of the copolymer. Compared with partially hydrolyzed polyacryamide (HPAM), the copolymer shows a much higher thickening capability and a much greater ability to resist shearing, heat, and salts. This good property of the copolymer is attributed to its three-dimensional dimensional network structure. According to the core flooding test, it can be obtained that oil recovery is enhanced about 4.3% by the copolymer flooding contrasted to the HPAM flooding in mid-low permeability cores under conditions of 1500 mg/L of polymers and 45°C. All the results prove that the copolymer has the capability of increasing oil recovery by improving waterflood sweep efficiency in high-salinity reservoirs.     

Experimental Study of Microscopic Displacement Efficiency of Polymer Microspheres Using Low-Field NMR

For reservoirs in high water cut exploitation period, profile control and water plugging is one of the important ways to improve oil recovery. Cores with different permeability were flooded to analyze the displacement results and displacement mechanisms for different grain size of polymer microspheres. Fluid distribution in cores was measured by NMR spectroscopy after water flooding, polymer microspheres flooding, and subsequent water flooding. The range of pore sizes from which oil was swept out was also calculated. The results showed that microspheres can effectively sweep remaining oil in different pore size of the cores. The suitability of different grain size of polymer microspheres with cores is different, microspheres with micron size are suitable for high-permeability cores, and microspheres with nanometer size are suitable for low-permeability cores.     

The displacement efficiency and rheology of welan gum for enhanced heavy oil recovery

The displacement efficiency of welan gum on enhanced heavy oil recovery has been investigated by comparing that of xanthan gum which is commonly used for polymer flooding, and it is found that the displacement efficiency of biopolymer welan gum is higher (>7.0 % at the normal permeability) than that of xanthan gum. In‐depth rheological investigations show that both storage modulus and loss modulus of welan gum solution are higher than those of xanthan gum solutions at the same concentration, temperature and salinity. The higher displacement efficiency for enhanced heavy oil recovery by welan gum is mainly caused by its stronger ability to form aggregates. Although the molecular weight of welan gum is lower than that of xanthan gum, the aggregates of welan gum molecules help to improve the sweep efficiency. It is proposed that welan gum improves oil recovery by drawing and dragging on the residual oils which is derived from the interlinked network structures formed by the adjacent double helices in the arrangement of the zipper model. The intermolecular structures formed by zipper model are stable in high temperature and high salinity condition. Copyright © 2014 John Wiley & Sons, Ltd.     

Synthesis and characterization of a novel amphiphilic copolymer containing β-cyclodextrin

In this article, maleic anhydride was used to attain the modified β-cyclodextrin (MAH-β-CD), and the MAH-β-CD was copolymerized with acrylamide (AM), acrylic acid (AA), and 2-acrylamido-2-methyl propane sulfonic acid (AMPS) via free radical copolymerization. The polymerization conditions were optimized through single-variable method. Subsequently, the copolymer structure was characterized through Fourier transform infrared (FTIR) spectroscopy, proton nuclear magnetic resonance (¹HNMR) spectroscopy, and scanning electron microscopy (SEM). The three-dimensional network structure formed in aqueous solutions was observed via experimental results of SEM. Subsequently, several aspects of the properties of the copolymer, such as temperature tolerance, shear tolerance, salt resistance, and oil displacement ability, were investigated by comparing with hydrolyzed polyacrylamide (HPAM). Results indicate that the copolymer showed better performances than HPAM; thus, it could be concluded that the introduction of β-cyclodextrin in the polymer chain was helpful in enhancing the oil displacement efficiency in high-temperature and high-salinity oil field.     

可用于尾矿库区污染控制的生态修复剂的制备及性能研究

采用种子乳液聚合法,以水性聚氨酯为分散液,醋酸乙烯酯(VAc)、马来酸二丁酯(DBM)、丙烯酸(AA)为主单体,2-丙烯酰胺基-2-甲基丙磺酸(AMPS)为功能单体,成功制备了羧基型共聚乳液,进一步考察了AMPS用量对乳液基本性能的影响,并首次将其用于尾矿库区的生态修复。实验结果表明:当AMPS用量在3%时,该共聚乳液用于尾矿库区固定尾砂的效果最好,且该共聚乳液形成胶膜的拉伸强度与固定尾砂时抗压强度呈现正相关性。另外,通过共聚乳液对尾砂的抗热老化、抗冻耐温、保水性及固定重金属离子稳定性等研究发现,羧基型共聚乳液能够有效实现尾矿库区的污染控制。微生物实验说明,羧基型共聚乳液作为尾矿库区修复剂使用时,具有良好的生态效应。这表明所制备的羧基型共聚乳液能够用于尾矿库区的污染控制与生态修复。     

预交联凝胶调驱剂的研究现状与应用进展

综述了预交联凝胶调驱剂的实验室合成研究和矿场应用进展,重点介绍了PPG性能改良（包括耐温耐盐性能、柔性弹性及小尺度智能材料及缓膨性能改良）及预交联凝胶调驱剂在高盐高温油藏、低温低盐砂岩厚油层、聚驱应用及复合使用弱凝胶封堵高渗区域和大裂缝中的应用。并对预交联凝胶调驱剂的发展方向进行了展望。参考文献48篇。     

用深部处理剂JY-8提高注聚区残余聚合物的利用率

针对目前各油田聚合物驱转为水驱后,一般出现含水上升快,产油量大幅度下降的情况,以及油层内残余的大量聚合物未得到利用,而目前开发的残余聚合物再利用技术存在一些缺点,未得到推广应用,研制出新型复合处理剂JY-8。新型复合处理剂JY-8可与聚合物形成强度较高的凝胶体,将地层内残余聚合物有效地固定和絮凝,是很好的固定剂和絮凝剂,实现了“二剂合一”,达到对地层进行深部调剖、驱油的目的;同时,通过调整复合处理剂JY-8的加量等可调节成胶时间和凝胶强度。室内评价和现场应用表明,与以前的技术相比,复合处理剂JY-8可使油层内的残余聚合物利用率从原来的8％提高到15.65％,使聚合物驱后续水驱的采收率增加值从原来的10.33％提高到18.1％,在油井上起到了很好的增油、控水效果。     

Preparation, morphology and properties of nanocomposites of polyacrylamide copolymers with monodisperse silica

To improve oil recovery (IOR) performance of polyacrylamide polymer media, the paper presented the nanocomposites (PA-B-S) of acrylamide-styrene-AMPS copolymers (PA-S) with monodisperse SiO₂ particles. The monodisperse particles from 17 to 100 nm with low size deviation were adopted as an inorganic phase, and their nanocomposite properties and morphology were investigated with viscosity measurements, thermal degradation (TGA), flooding test and transmission electron microscopy (TEM) techniques. For 66.7 nm SiO₂ particles at 0.5 wt% load, the nanocomposites produced viscosity enhancement at critical concentration, high salt-tolerance behavior, and the high degradation temperature at 411 °C, which were obviously higher than those of pure PA-S copolymers. These inorganic-organic synergistic or nano size effects were shown in a series of prepared nanocomposite samples. TEM morphology proved that PA-B-S solution at LCST formed uniform dispersion of the SiO₂ particles encapsulated with this associating copolymer and formed stable drop-like emulsion patterns.In flooding experiments, the PA-B-S solutions at critical viscosity gave the resistance factor of 9.38 and residual resistance factor of 3.39, compared with those of 5.20, 1.51 for pure PA-S, respectively. Such improved properties of PA-B-S were suitable for producing high shearing behavior and sweep volume in IOR or EOR. As the controllable characters of monodisperse SiO₂ particles, the results from their nanocomposites were the good references to the multi-disperse particles acted as IOR media.     

Influence on Emulsification in Binary Flooding of Oil Displacement Effect

As one of the important mechanisms of EOR for SP binary flooding, emulsification attracts much attention of researchers. But there have not yet unified methods or clear understandings of evaluation of the emulsion function on flooding system and emulsification's impact on enhanced oil recovery. A comprehensive evaluation method of emulsifying properties is established in this paper for the first time. It characterizes the emulsifying properties of different flooding system by using the emulsifying integrated index, and examines the corresponding core flooding results of different emulsifying properties. Results of Berea core test show that the flooding system runs better with a higher emulsifying composite index in cores whose permeability is 300 ～ 400 mD. When emulsifying integrated index increases from 23.9% to 80.2%, the corresponding oil displacement efficiency reaches 12%. When emulsifying integrated index is under the medium level of 50% or less, the SP flooding system efficiency increases rapidly with the index changes, then increases slowly. The influencing rule of emulsification of SP binary flooding is obtained in this paper, which is important to optimize the formulation of SP binary flooding system, provide an important basis and technical support for the design of field experiments and SP flooding promotion.     

Mechanism for viscoelastic emulsion displacing oil film – A numerical simulation approach

The reservoir characteristics and fluid property of Daqing reservoir were taken as the research platform. For simulating the emulsifying process in the reservoir, injecting different concentrations of emulsifier solution into the core after water flooding, the viscoelasticity of the emulsion was measured. According to the value of the emulsion viscoelasticity, the numerical model of emulsion displacing oil film was established. Elastic stress acting on the oil film was calculated when the emulsion migrates. The deformation and transportation of the oil film were analyzed at bearing the elastic stress. The results show that the emulsion has favorable viscoelasticity. When the emulsifier concentration is higher, the emulsion elasticity is favorably increased. The oil film can deform and transport forward by the elastic stress. The elastic stress increases as the emulsion elasticity increases.     

Coreflooding and Pore-Scale Visualization of Foamed Gel Flowed in Porous Network Media

To investigate the mechanisms of enhancing oil recovery and the flow behaviors of foamed gel in porous media, foamed gels with characteristics of excellent strength and viscosity were prepared with polymer, crosslinking agent, foam agent, and formation water. The breakthrough-vacuum method and a rotary viscometer were used to evaluate the strength and viscosity of foamed gel. Coreflooding and pore-level visualization experiments were performed in heterogeneous reservoir models. Laboratory results illustrate that high strength and viscosity of foamed gel can be prepared by 0.15% NJ-8, 0.2% polyacrylamide solution, and 1.5% foaming agent. The strength and viscosity of the foamed gel reached 0.06 MPa and 10,000 MPa · s, respectively. The results of coreflooding experiments in heterogeneous cores show that oil recovery can be improved by approximately 36.9% after injecting 0.3 pore volume of the foamed gel, and enhanced oil recovery is mainly attributed to the improving sweep efficiency of mid- to low-permeability layers. Images of visualization flooding demonstrate that foamed gel exhibits good oil resistance and elasticity when used with crude oil. Furthermore, the new amoeba effect, Jamin effect, fluid-diverting effect, and extruding effect between foamed gel and oil in porous media can enhance oil recovery by improving sweep efficiency.     

Experimental Study on Stability and Improving Sweep Efficiency with Microfoam in Heterogeneous Porous Media

In this paper, we attempted to prepare microfoam by using a sandpack filled with glass beads with co-flowing gas and foaming solution, the microfoam stability and effectiveness in improving profile control capacity at micromodel and pore media were evaluated by micromodel tests and double-core experiments. The results of micromodel tests showed that microfoam stability was increased with increasing xanthan gum concentration due to a higher solution viscosity and viscoelasticity of liquid film. The xanthan gum-stabilized microfoam had a longer propagation distance through the low permeable region of heterogeneous micromodel at time of breakthrough than common microfoam, the optimum performance of microfoam for fluid diversion was multiple bubble trapping and mobilization rather than lamella division. According to the results of double-core experiments, the microfoam could plug the high permeability sandpack and improve the sweep efficiency in the low permeability sandpack, which could improve the water injection profile of porous media effectively. The increase in profile control effects had a good correspondence with the increase of xanthan gum concentration. The presented results were useful in understanding and designing microfoam injection in reservoirs for enhanced oil recovery.     

High-temperature wine making using the thermotolerant yeast strain Kluyveromyces marxianus IMB3

Kluyveromyces marxianus IMB3 yeast cells were immobilized on delignified cellulosic material, apple, and quince separately. Both immobilized and free cells were used in high-temperature wine making, and their fermented grape must contained 3 to 4% alcohol. Semisweet wines were produced by the addition of potable alcohol to the fermented must. Preliminary sensory evaluation of the produced semisweet wines showed good flavor and aroma. The final product contained extremely low levels of higher and amyl alcohols while ethyl acetate was at levels usually present in wines. The ferment produced may be blended with other products to improve their quality.     

Investigating the generation of ferrous sulfide nanoparticles in the produced fluid after acidizing oil wells and its influence on emulsifying stability between oil and water

Studies show that after acidizing operation of oil wells using the alkali/surfactant/polymer (ASP) flooding technology, the produced fluid is emulsified. Since the produced emulsion is stable, it affects the oil–water separation performance. In order to analyze the generation of stable emulsion in the produced fluid after acidizing an oil well, innovative separation experiments were carried out on real oil wells. During the experiments, solid particles in the middle layer of the emulsifying system in the produced fluid after acidizing ASP flooding were extracted and characterized. The generation of the stable emulsifying system in the produced fluid was studied through stability experiments and molecular dynamics simulations. The results showed that the synergistic effect of ferrous sulfide nanoparticles and surfactants was the fundamental reason for the strong emulsifying stability of the produced liquid after acidizing of the ternary composite system. The generation of ferrous sulfide solid particles mainly included two steps. First, sulfate reducing bacteria in injected water by ASP flooding reacted with sulfate in formation water to form hydrogen sulfide. Then, the hydrogen sulfide reacted with iron metal in oil wells and casing of wellbore to form ferrous sulfide particles. It was found that surfactants are adsorbed on the surface of ferrous sulfide nanoparticles. Subsequently, the control ability of surfactant on oil and water phases in the liquid film was enhanced. The performed analyses demonstrate that the adsorption of solid particles to the oil phase was enhanced, while the free motion of molecules in the oil phase at the liquid film position was weakened. The strength of the interfacial film between oil and water was further increased by the synergistic effect of ferrous sulfide nanoparticles and surfactant. The present study is expected to provide a guideline for a better understanding of the efficient treatment of produced fluids in ASP flooding.