Surfactant induced reservoir wettability alteration: Recent theoretical and experimental advances in enhanced oil recovery

Reservoir wettability plays an important role in various oil recovery processes.The origin and evolution of reservoir wettability were critically reviewed to better understand the complexity of wettability due to interactions in crude oil-brine-rock system,with introduction of different wetting states and their influence on fluid distribution in pore spaces.The effect of wettability on oil recovery of waterflooding was then summarized from past and recent research to emphasize the importance of wettability in oil displacement by brine.The mechanism of wettability alteration by different surfactants in both carbonate and sandstone reservoirs was analyzed,concerning their distinct surface chemistry,and different interaction patterns of surfactants with components on rock surface.Other concerns such as the combined effect of wettability alteration and interfacial tension (IFT) reduction on the imbibition process was also taken into account.Generally,surfactant induced wettability alteration for enhanced oil recovery is still in the stage of laboratory investigation.The successful application of this technique relies on a comprehensive survey of target reservoir conditions,and could be expected especially in low permeability fractured reservoirs and forced imbibition process.     

Silica nanofluid flooding for enhanced oil recovery in sandstone rocks

Enhanced oil recovery is proposed as a solution for declining oil production. One of the advanced trends in the petroleum industry is the application of nanotechnology for enhanced oil recovery. Silica nanoparticles (SiNPs) are believed to have the ability to improve oil production, while being environmentally friendly and of natural composition to sandstone oil reservoirs.In our work, we investigated the effect of silica nanoparticles flooding on the amount of oil recovered. Experiments were carried using commercial silica of approximately 20 nm in size. We used sandstone cores in the core flooding experiments. For one of the cores tertiary recovery is applied where brine imbibition was followed by nanofluid imbibition. While in the other cores secondary recovery was applied where primary drainage is directly followed by nanofluid imbibition. We investigated the effect of concentration of nanofluid on recovery; in addition, residual oil saturation was obtained to get the displacement efficiency. Silica nanofluid of concentration 0.01 wt%, 0.05 wt%, 0.1 wt% and 0.5 wt% were studied.The recovery factor improved with increasing the silica nanofluid concentration until optimum concentration was reached. The maximum oil recovery was achieved at optimum silica nanoparticles concentration of 0.1 wt%. The ultimate recovery of initial oil in place increased by 13.28% when using tertiary flooding of silica nanofluid compared to the recovery achieved by water flooding alone. Based on our experimental study, permeability impairment was investigated by studying the silica nanoparticles concentration, and the silica nanofluid injection rate. The permeability was measured before and after nanofluid injection. This helped us to understand the behavior of the silica nanoparticles in porous media. Results showed that silica nanofluid flooding is a potential tertiary enhanced oil recovery method after water flooding has ceased.     

Microbial improved oil recovery—bacterial induced wettability and interfacial tension effects on oil production

Microbial Improved Oil Recovery (MIOR) utilizes the effect of oil degrading bacteria that grow on the oil–water interface. It has been demonstrated that the presence of growing bacteria in an oil and water saturated sandstone core can result in significant increased oil recovery upon water flooding [Torsvik, T., Gilje, E. and Sunde, E., Aerobic Microbial Enhanced Oil Recovery, Paper presented at the 5th International Conference on Microbial Enhanced Oil Recovery, Dallas TX, USA, Sep. 11, 1995]. Several mechanisms are proposed to explain this observed effect, among which are reduction in the oil–water interfacial tension (IFT) and changes in the wettability of the system. The experimental results from the present study indicate that bacterial growth can both reduce IFT and change the wettability towards less water-wet conditions. A subsequent simulation study shows that a change in wettability towards a less water-wet behavior can reproduce the increased oil recovery observed during the core flood reported by Torsvik et al. Furthermore, the simulations also indicate that a gradual and strong reduction in IFT can reproduce the same experimental data. Both the effect of changed wettability and reduction in IFT was included in the simulation model as changes to the relative permeability curves, constructed from general theory on IFT reduction and wettability alteration.     

原油组分对化学驱表面活性剂界面张力的影响

为提高化学驱油技术的使用效率,有效掌握表面活性剂的界面张力变化因素,开展了原油组分对表面活性剂界面张力的影响研究。应用原油分离提纯技术、GC-MS、红外光谱和核磁共振分析方法,从原油中分离出石油酸,分析其组分间的相互关系,总结界面张力变化规律。实验结果表明,原油组分中石油酸是影响界面张力的主要成分,其中异构脂肪酸是降低界面张力的重要贡献者。     

The effects of interfacial tension,injection rate,and permeability on oil recovery in dilute surfactant flooding

Surfactant flooding as a potential enhanced oil recovery technology in depleted reservoirs after water flooding has been documented for several decades and has attracted extensive attention. This research explored the effect of interfacial tension among crude oil and surfactant, injection rate, and permeability on oil recovery in dilute surfactant flooding. The results indicated that the additional oil recovery increased with the reduction of the interfacial tension and the increase of the permeability. The additional oil recovery increased and later decreased with the increase of injection rate. The research is instructive for surfactant flooding application for enhanced oil recovery.     

Improvement of heavy oil recovery and role of nanoparticles of clay in the surfactant flooding process

Increasing demand and dwindling supply of crude oil have spurred efforts toward enhancing heavy oil recovery. Recently, applications of nanoparticles (NPs) for heavy oil recovery have been reported. In this study, the use of clay NPs is investigated for enhanced oil recovery. Surfactant solutions and newly developed nanosurfactant solutions with 1600–2000 ppm SDS were tested. The crude oil had a viscosity of 1320 mPa.sec at test conditions. In this study, the role of NPs in the adsorption of surfactant onto solid surfaces of reservoir core is studied. The core flooding experiments showed high potential of using nanoclay for enhancing heavy oil recovery, where 52% of surfactant flooded heavy oil was recovered after injecting the NPs solvent. Moreover, nanoclay has generally better performance in enhancing the oil recovery at surfactant solution, near CMC conditions. The nanoclay surfactant solutions improved oil recovery. The nanoclay, however, showed improved performance in comparison with clay.     

Synthesis hydrophilic hybrid nanoparticles and its application in wettability alteration of oil-wet carbonate rock reservoir

In this study, synthesized SiO₂/ZnO hybrid nanoparticles were used to change the wettability of carbonate rock from highly oil-wet to strongly water-wet state. The SiO₂/ZnO nanoparticles were synthesized by modified sol-gel method. In this method, TEOS was used to increase the functional groups on the surface of the ZnO nanoparticles to produce highly hydrophilic nanoparticles. The contact angle measurements were conducted on the rock surface before and after nano-treatment. The contact angle of oil droplet with the rock changed from 0° to 150°, 161°, 164° and 170° after impregnation the rock with 0.01, 0.033, 0.07 and 0.33 wt.% nanofluids.     

无碱二元体系的黏弹性和界面张力对水驱残余油的作用

三元复合驱含碱驱油体系会大幅度降低聚合物溶液的黏弹性,引起地层粘土分散和运移、形成碱垢及导致地层渗透率下降。为此提出利用不加碱可形成超低界面张力的聚合物/甜菜碱表面活性剂二元复合体系驱油。通过流变性实验及微观模型驱油实验,分析了表面活性剂对聚合物表面活性剂二元复合体系黏弹性的影响和聚合物表面活性剂二元复合体系的黏弹性及界面张力对采收率的影响。对聚合物表面活性剂二元复合体系提高水驱后残余油采收率机理的研究表明:在驱替水驱后残余油过程中,聚合物表面活性剂二元复合体系利用了聚合物溶液的黏弹特性和表面活性剂的超低张力界面特性,水驱后残余油以油丝和乳状液形式被携带和运移,随着二元驱油体系的黏弹性的增加和界面张力的降低,水驱后二元驱后的采收率增加,降低界面张力的驱油效果(指达到超低)比提高体系的黏弹性的效果更明显。     

Application of ion-engineered Persian Gulf seawater in EOR:effects of different ions on interfacial tension,contact angle,zeta potential,and oil recovery

In this study,we initially performed interfacial tension(IFT)tests to investigate the potential of using the Persian Gulf sea-water(PGSW)as smart water with dif...     

Feasibility study on application of the recent enhanced heavy oil recovery methods (VAPEX,SAGD, CAGD and THAI) in an Iranian heavy oil reservoir

Enhanced oil recovery (EOR) methods assisted by gravity drainage mechanism and application of sophisticated horizontal wells bring new hope for heavy oil extraction. Variety of thermal and non-thermal EOR techniques inject an external source of energy and materials such as steam, solvent vapor, or gas through a horizontal well at the top of the reservoir to reduce in-situ heavy oil viscosity. So, the diluted oil becomes mobile and flows downwards by gravity drainage to a horizontal producer located at the bottom of the reservoir.

In this paper, a sector model of an Iranian fractured carbonate heavy oil reservoir was provided to simulate and evaluate capability of some EOR techniques such as Vapor Extraction (VAPEX), Steam Assisted Gravity Drainage (SAGD), Combustion Assisted Gravity Drainage (CAGD), and Toe to Heel Air Injection (THAI) at its reservoir conditions and fluid properties. The simulation results demonstrated that wet CAGD in comparison with other nominated methods could improve heavy oil recovery factor to around 19% much more than each of SAGD, THAI, and VAPEX techniques. It could also reduce the total energy to produced oil ratio index up to 82% with respect to SAGD process in a year.

Although lower oil recovery has been gained by VAPEX process, but using a proper vaporized solvent could produce a kind of de-asphalted and upgraded oil with increased API gravity up to 29°API with no considerable solvent loss.     

乐安油田草4块稠油热水驱及热化学驱实验研究

利用化学驱物理模拟流程装置及填砂管模型研究了乐安油田草4块不同温度下稠油的热水驱与热化学驱的驱油效果及变化规律.结果表明,提高油藏注入水的温度,可以明显降低原油粘度,提高稠油的采收率.而对于油水界面张力达到超低(10<'-3>mN/m数量级)的热化学驱,虽然通过油水界面张力降低,提高了驱油效果,但由于驱替通道阻力减小,后期实际驱替液流动的波及体积减小,导致最终采收率与同温度下单纯水驱相比低3%-5%.因此,单纯的热化学驱不适合乐安油田草4块稠油开发.