Synergistic anionic/zwitterionic mixed surfactant system with high emulsification efficiency for enhanced oil recovery in low permeability reservoirs

Emulsification is one of the important mechanisms of surfactant flooding. To improve oil recovery for low permeability reservoirs, a highly efficient emulsification oil flooding system consisting of anionic surfactant sodium alkyl glucosyl hydroxypropyl sulfonate(APGSHS) and zwitterionic surfactant octadecyl betaine(BS-18) is proposed. The performance of APGSHS/BS-18 mixed surfactant system was evaluated in terms of interfacial tension, emulsification capability, emulsion size and distribution, wettability alteration, temperature-resistance and salt-resistance. The emulsification speed was used to evaluate the emulsification ability of surfactant systems, and the results show that mixed surfactant systems can completely emulsify the crude oil into emulsions droplets even under low energy conditions. Meanwhile,the system exhibits good temperature and salt resistance. Finally, the best oil recovery of 25.45% is achieved for low permeability core by the mixed surfactant system with a total concentration of 0.3 wt%while the molar ratio of APGSHS:BS-18 is 4:6. The current study indicates that the anionic/zwitterionic mixed surfactant system can improve the oil flooding efficiency and is potential candidate for application in low permeability reservoirs.

A novel profile modification HPF-Co gel satisfied with fractured low permeability reservoirs in high temperature and high salinity

Conformance control and water plugging are a widely used EOR method in mature oilfields.However,majority of conformance control and water plugging agents are unavoidable dehydrated situation in high-temperature and high-salinity low permeability reservoirs.Consequently,a novel conformance control system HPF-Co gel,based on high-temperature stabilizer(CoCl_(2)·H_(2)O,CCH)is developed.The HPF-Co bulk gel has better performances with high temperature(120℃)and high salinity(1×10^(5)mg/L).According to Sydansk coding system,the gel strength of HPF-Co with CCH is increased to code G.The dehydration rate of HPF-Co gel is 32.0%after aging for 150 d at 120℃,showing excellent thermal stability.The rheological properties of HPF gel and HPF-Co gel are also studied.The results show that the storage modulus(G′)of HPF-Co gel is always greater than that of HPF gel.The effect of CCH on the microstructure of the gel is studied.The results show that the HPF-Co gel with CCH has a denser gel network,and the diameter of the three-dimensional network skeleton is 1.5-3.5μm.After 90 d of aging,HPF-Co gel still has a good three-dimensional structure.Infrared spectroscopy results show that CCH forms coordination bonds with N and O atoms in the gel amide group,which can suppress the vibration of cross-linked sites and improve the stability at high temperature.Fractured core plugging test determines the optimized polymer gel injection strategy and injection velocity with HPF-Co bulk gel system,plugging rate exceeding 98%.Moreover,the results of subsequent waterflooding recovery can be improved by 17%.

Advances in enhanced oil recovery technologies for low permeability reservoirs

Low permeability oil and gas resources are rich and have great potential all over the world, which has gradually become the main goal of oil and gas development. However, after traditional primary and secondary exploitation, there is still a large amount of remaining oil that has not been recovered.Therefore, in recent years, enhanced oil recovery(EOR) technologies for low permeability reservoirs have been greatly developed to further improve crude oil production. This study presents a comprehensive review of EOR technologies in low permeability reservoirs with an emphasis on gas flooding, surfactant flooding, nanofluid flooding and imbibition EOR technologies. In addition, two kinds of gel systems are introduced for conformance control in low permeability reservoirs with channeling problems. Finally,the technical challenges, directions and outlooks of EOR in low permeability reservoirs are addressed.

Research and Application of CO₂Flooding Enhanced Oil Recovery in Low Permeability Oilfield

This paper discusses the new progress and field application of CO2 flooding in low permeability reservoirs enhanced oil recovery. The study shows that CO2 flooding can improve the oil recovery rate of low permeability oilfield by more than 10%. The practice shows that the liquid CO2 injection in low permeability reservoir is easier than water injection, and the reservoir generally has better CO2 storage.

Liquid injectivity in a SAG foam process:Effect of permeability

Foam is utilized in enhanced oil recovery and CO_(2) sequestration.Surfactant-alternating-gas(SAG)is a preferred approach for placing foam into reservoirs,due to it enhances gas injection and minimizes corrosion in facilities.Our previous studies with similar permeability cores show that during SAG injection,several banks occupy the area near the well where fluid exhibits distinct behaviour.However,underground reservoirs are heterogeneous,often layered.It is crucial to understand the effect of permeability on fluid behaviour and injectivity in a SAG process.In this work,coreflood experiments are conducted in cores with permeabilities ranging from 16 to 2300 mD.We observe the same sequence of banks in cores with different permeabilities.However,the speed at which banks propagate and their overall mobility can vary depending on permeability.At higher permeabilities,the gas-dissolution bank and the forced-imbibition bank progress more rapidly during liquid injection.The total mobilities of both banks decrease with permeability.By utilizing a bank-propagation model,we scale up our experimental findings and compare them to results obtained using the Peaceman equation.Our findings reveal that the liquid injectivity in a SAG foam process is misestimated by conventional simulators based on the Peaceman equation.The lower the formation permeability,the greater the error.

Study on Reducing Injection Pressure of Low Permeability Reservoirs Characterized by High Temperature and High Salinity

In view of the problems of high injection pressure and low water injection rate in water injection wells of low permeability reservoirs featuring high temperature and high salinity,two new surfactants were synthesized,including a quaternary ammonium surfactant and a betaine amphoteric surfactant.The composite surfactant system BYJ-1 was formed by mixing two kinds of surfactants.The minimum interfacial tension between BYJ-1 solution and the crude oil could reach 1.4×10^(-3) mN/m.The temperature resistance was up to 140℃,and the salt resistance could reach up to 120 g/L.For the low permeability core fully saturated with water phase,BYJ-1 could obviously reduce the starting pressure gradient of low permeability core.While for the core with residual oil,BYJ-1 could obviously reduce the injection pressure and improve the oil recovery.Moreover,the field test showed that BYJ-1 could effectively reduce the injection pressure of the water injection well,increase the injection volume,and increase the liquid production and oil production of the corresponding production well.

Low-tension gas process in high-salinity and low-permeability reservoirs

Polymer-based EOR methods in low-permeability reservoirs face injectivity issues and increased fracturing due to near wellbore plugging,as well as high-pressure gradients in these reservoirs.Polymer may cause pore blockage and undergo shear degradation and even oxidative degradation at high temperatures in the presence of very hard brine.Low-tension gas(LTG) flooding has the potential to be applied successfully for low-permeability carbonate reservoirs even in the presence of high formation brine salinity.In LTG flooding,the interfacial tension between oil and water is reduced to ultra-low values(10^-3 dyne/cm) by injecting an optimized surfactant formulation to maximize mobilization of residual oil post-waterflood.Gas(nitrogen,hydrocarbon gases or C02) is co-injected along with the surfactant slug to generate in situ foam which reduces the mobility ratio between the displaced(oil) and displacing phases,thus improving the displacement efficiency of the oil.In this work,the mechanism governing LTG flooding in low-permeability,high-salinity reservoirs was studied at a microscopic level using microemulsion properties and on a macroscopic scale by laboratory-scale coreflooding experiments.The main injection parameters studied were injected slug salinity and the interrelation between surfactant concentration and injected foam quality,and how they influence oil mobilization and displacement efficiency.Qualitative assessment of the results was performed by studying oil recovery,oil fractional flow,oil bank breakthrough and effluent salinity and pressure drop characteristics.

Displacement of Oil in a Porous Medium on Diphasic Flow by Water Injection

The purpose of this article is to show the role and influence of fluid injection, porosity on two-phase flows in porous media for the purpose of improving and increasing recovery efficiency assisted by oil. An experimental study was carried out in porous media, it is a plexiglass cylinder filled with sands saturated with crude oil. Pressure drop and data processing for two-phase flow are measured and processed using a differential pressure sensor connected to an acquisition computer. It thus makes it possible to determine the pressure difference between the inlet and the outlet of the porous medium over time. In this experiment, the flow rates at the inlet and the outlet of the porous medium were measured as a function of time using a flow rate and a pump. To describe these flows we will use Darcy’s model.

低渗透油藏压驱技术现状及发展趋势

压驱技术是近年来针对低渗透油藏高效开发而提出的一种增加储层动用程度、提高原油采收率的储层改造技术。压驱技术先通过高压小排量向地层注入大量携带化学剂的液体,然后进行焖井,通过压力的扩散和化学剂与裂缝孔隙中的原油充分置换而达到增产的目的。文中结合国内外压驱技术的最新研究动态,从压驱技术现状、设计原则、设计方法、应用分析及发展趋势等方面展开论述,重点分析了压驱技术与水力压裂技术的区别、增产机理和设计方法以及现场应用效果等,同时也指出了当前压驱技术理论研究方面的欠缺,展望了该技术的发展趋势和应用前景。

乳化沥青提高原油采收率研究进展

乳化沥青具有注入性能好、封堵强度高等优点,作为一种选择性堵剂在油田提高采收率领域比其他化学剂体系更具应用潜力。本文总结了国内乳化沥青堵水体系的开发历程及现场选择性堵水的应用效果。通过调研近年来国内外文献,概述了乳化沥青堵水的作用机理,一种是作为乳液的作用机理,主要是乳液颗粒被变形捕获产生贾敏效应和乳液液滴的机械滞留使水的流动阻力增大;另一种是其分散相也就是乳液破乳后沥青的作用机理,主要是沥青黏附在岩壁上起到的堵水作用。同时,总结了乳化沥青稳定的主要影响因素,包括温度、水相中的电解质浓度和pH值以及分散相中的沥青质,并且论述了各因素影响乳化沥青稳定性的作用机理。最后,详细叙述了乳化沥青应用于油田调剖堵水领域的最新研究进展,研究表明乳化沥青不仅具有优异的封堵效果,还具有独特的封堵选择性。此外,乳化沥青还能与CO_(2)吞吐、泡沫调驱组成复合增产技术进行现场应用,并且指出了乳化沥青应用于调剖堵水领域存在的问题与未来展望。

稠油油藏大段塞调驱后提高采收率新技术及应用

H1块为普通稠油区块,开展多轮次调驱后,取得较好的增油效果。但随着大段塞调驱剂注入,后期压力维持在较高水平,含水率持续上升,同时注入井吸水能力下降,油井产液能力下降,产量递减加大,亟需有效开发接替技术。为进一步改善开发现状,室内设计了在大段塞调驱段塞后,注入降黏剂进一步提高采收率。室内通过大量实验,筛选出了具有良好降黏性以及界面活性降黏剂JN-1,当质量分数达到0.2%时,降黏率可达82.0%,降低油水界面张力至4.72×10^(-3)mN·m^(-1)。室内物模实验表明,在注入0.3PV调驱段塞后,继续注入0.2%降黏剂段塞0.3PV,可充分启动残余油,进一步提高采收率16.8%。现场开展降黏驱4井组先导实验,设计注入质量分数0.2%、0.14 PV降黏剂,注入后平均单井日增油0.8 t,综合含水率下降6%。

油藏微生物在CCUS领域的应用前景

CCUS是应对全球环境问题的关键技术,也是能源行业实现绿色低碳发展的重要途径。目前能源行业开展CCUS技术中还存在一些难题,其中CO_(2)驱替技术普遍存在气窜严重,驱替效率低的难题;CO_(2)封存方面也存在地面、注入井泄漏及封存效率低等难题。这些问题是制约我国CCUS技术工业化推广的瓶颈。作为CO_(2)驱替、封存的主要场所,油藏等地下环境存在种类丰富的微生物类群。国内外相关机构和研究人员开展了大量研究,室内模拟及现场试验证实地下环境中的微生物类群以不同的方式参与CO_(2)地下循环及封存过程,其中腐生菌、厌氧发酵菌、产甲烷古菌与CO_(2)代谢直接相关,它们可以将油藏作为厌氧反应器,通过代谢协同促进CO_(2)的CH_(4)转化,实现资源化利用;同时油藏中普遍存在的硫酸盐还原菌、铁还原菌、硝酸盐还原菌等微生物通过菌体代谢过程参与CO_(2)的封存过程,促进CO_(2)的结构封存、溶解封存和矿化封存。此外,一些微生物可以在地下产生大分子胞外多糖及生物膜结构封堵地下大孔隙及裂缝结构,改善地层非均质,缓解CO_(2)驱替过程中的窜流及CO_(2)封存泄漏难题,从而大幅提高CO_(2)驱效率和封存效率。生物技术是一项绿色、低碳、低成本的高新技术领域,在不同产业中都发挥着重要的作用,开展CO_(2)与地下微生物间的互作机理研究,加快微生物技术在CCUS技术领域的应用研究,可以有效解决CCUS关键环节的技术瓶颈,提高CCUS地下各环节的效率,对CCUS技术的发展具有非常重要的意义。

高温中低渗油藏智能纳米黑卡驱提高采收率技术

当前化学驱储量接替严重不足,亟需攻关突破高温中低渗油藏提高采收率技术。智能纳米黑卡驱油技术是当下极具前瞻性的纳米驱油技术,可大幅度提高采收率。针对河南油田高温中低渗油藏,开展高温条件下纳米黑卡静态性能评价,并通过高温岩心驱替实验评价不同渗透率条件下智能纳米黑卡驱油效果。结果表明,智能纳米黑卡具有优异的耐高温性能,分散稳定性好,能够降低油水界面张力至10^(-1)mN/m,并具有改变润湿性和快速乳化与破乳性能。同时,纳米黑卡具有高效的洗油能力,在95℃下注入0.3 PV的质量分数为0.005%的智能纳米黑卡溶液,在目标油田不同渗透率(50×10^(-3)~450×10^(-3)μm^(2))条件下可提高采收率15.8百分点~20.0百分点。因此,智能纳米黑卡驱油技术适用于河南油田高温中低渗油藏提高采收率。

苏北盆地石港特低渗储层微观特征及提高采收率对策研究

苏北盆地石港油田属低孔、特低渗砂岩油藏,油井自然产能低,采用水力压裂后注水开发可提高产油能力,但油田开发中呈现低采油速度、低采出程度和开发效果差的特点,开发矛盾加剧。因此,需明确低效开发原因,探究提高采收率对策,为提高石港油田开发效果提供理论依据。通过全岩矿物成分分析、气测岩心孔渗参数、岩心敏感性评价等方法,从岩石矿物组成、孔喉结构和岩石敏感性等方面分析了其储层的微观特性;通过油藏数值模拟以及室内岩心实验研究了压裂水驱后剩余油的分布特征;通过核磁共振在线驱替实验探究了提高采收率的对策。结果显示,储层岩心呈现出典型的低孔、特低渗特征,且在开发过程中具有一定的速度敏感性和水敏感性。压裂水驱后,岩心中剩余油主要分布在0.01~1μm中小孔径的孔道中,使用表面活性剂驱及二次水驱将岩心中剩余油采收率提高了14.81%。储层渗透率特低、微孔隙和微裂缝发育、速敏、水敏等是其低效开发的主要原因。注水开发会导致岩石矿物膨胀、运移,增大流动阻力,所以区块经压裂水驱仅明显提高主流线上剩余油的采出程度,整体动用程度不高,剩余油仍有较多富集。建议采用化学驱及多轮次驱替以增强中小孔道中原油动用程度,进一步提升油田开发效果。

海上低渗油藏CO_(2)混相驱可行性实验研究

海上珠江口盆地陆丰凹陷低渗、特低渗储量丰富,水驱开发难度大,注气开发需求迫切。CO_(2)驱是提高采收率的主要技术之一,但目前海上CO_(2)综合利用方面应用较少。以陆丰凹陷L油藏为例,开展了目标油藏原油注CO_(2)驱油机理实验和长岩心CO_(2)驱油效果评价实验,重点对比CO_(2)注入前后原油相态特征的变化,并对不同开发方式驱油效果进行了对比优化研究,为目标油田CO_(2)驱可行性提供依据。实验结果表明,CO_(2)可以有效提高低渗油藏的开发效果,提高采收率幅度可以在水驱的基础上提高11.75%,交替驱可以作为后期注CO_(2)防窜和进一步提高采收率的技术手段。实验研究结果对海上低渗油藏CO_(2)注气开发提供技术支持。

DES+CTAB复配驱油剂体系提高低渗致密砂岩油藏采收率机理

针对低渗致密油藏注水困难、采收率低等问题,利用尿素基深共晶溶剂(DES)与十六烷基三甲基溴化铵(CTAB)复配的驱油剂体系,对驱油剂在低渗致密油藏中的降压增注和提高采收率机理进行了研究。研究结果表明:①驱油剂体系可以将油水界面张力降低至10^(-3)mN/m以下,大大提高了洗油效率;②驱油剂体系可有效抑制黏土矿物水化,避免了低渗致密砂岩中黏土矿物水化膨胀带来的流体敏感性损害;③驱油剂体系可对砂岩表面进行界面修饰,驱油剂溶液浸泡后样品的油相接触角由25.8°增加至61.4°,亲水性增强,亲油性减弱,有助于吸附在岩石孔隙壁面的油膜脱落;④超前注入驱油剂的注入压力降低率平均为79.64%,采收率平均为50.96%,远大于常规水驱(一次注水→注驱油剂驱→二次注水)的采收率。

纳米淀粉流体提高原油采收率

为了进一步促进纳米驱油技术在低渗透油藏中的高效应用,亟需开发新型的纳米驱油产品。纳米淀粉颗粒作为一种环境友好型的材料,分布广、价格相对低廉、性能优异,具备大幅度提高采收率的潜力。通过室内静态实验、岩心驱替实验、微观可视化实验、CT扫描实验等手段,从纳米淀粉流体的基本物性、提高驱油效果、扩大波及体积等方面研究了其提高采收率的过程和机理。研究结果表明,质量浓度为5000 mg/L的纳米淀粉流体因其亲水性和较小的粒径(30 nm)可改变水分子的赋存状态,使水相变温度从102℃升高至110℃,使得岩石表面的润湿接触角从78°降至34.2°,使油水界面张力从20 mN/m降至0.56 mN/m,注入压力下降39.6%。在微观可视化模型中,纳米淀粉流体可以明显降低多孔介质中的含油饱和度,特别是多孔介质固体表面的油膜量明显减少,提高驱油效果明显。在低渗透岩心中,纳米淀粉溶液的驱替前沿更加均匀,与水驱相比具有更大的波及体积。由于较大的波及体积、较高的驱油效率以及良好的润湿性等,注入0.4 PV质量浓度为5000 mg/L的纳米淀粉流体后,低渗透岩心的采收率增幅达21百分点。研究结果可为低渗透油藏的提高采收率提供一种新的技术参考。

原位二氧化碳泡沫驱提高采收率实验

原位CO_(2)泡沫驱是一种很有潜力的提高采收率技术。通过原位CO_(2)泡沫驱提高采收率实验,优化了生气体系、泡沫体系以及注入参数,得到了最佳的注入量、注入速度和适用的渗透率级差范围。研究结果表明,在温度为70℃,地层水矿化度为10 000 mg/L条件下,得到可以作用于地层深部的原位CO_(2)泡沫体系,其配方为:2.1%碳酸氢铵+1.6%醋酸+9.5%氯化铵+0.1%α-烯烃磺酸钠AOS+0.1%油酸酰胺丙基甜菜碱DHSB,泡沫体积可达810 mL,泡沫综合指数为15552 mL·min。该体系形成的泡沫在油藏中部具有较高黏度和较大弹性的特性,能够有效封堵高渗通道,表现出良好的封堵能力。在渗透率级差为6左右时,原位CO_(2)泡沫体系注入速度控制在1.0mL/min左右,注入段塞量控制在0.3 PV,能够发挥最佳的调驱效果。研究还发现,该泡沫体系在渗透率级差为3.9~13.7的非均质储层中能有效提高采收率,而在渗透率级差为15.6的条件下,虽然未能显著提高低渗层采收率,但在高渗管中仍然有一定的洗油作用。本研究为原位CO_(2)泡沫驱技术的应用和优化提供了重要参考。

改性片状纳米流体的洗油效率及机理

纳米流体提高采收率已然成为油气勘探开发的研究热点。利用研发的改性片状纳米流体,在自制的可视化模型中研究固体界面油膜在接触到质量浓度为50mg/L的改性片状纳米流体后的收缩规律,并开展油砂洗油实验,明确50mg/L的改性片状纳米流体在不同条件下的洗油效率。研究结果表明,模拟地层水环境下,固体界面油膜收缩速率较慢,并未出现楔形区域;改性片状纳米流体环境下,固体界面油膜在收缩过程中出现明显的楔形区域,且出现两条接触线:外接触线和内接触线,外接触线的收缩速率为8.5817×10^(-5)cm/s,内接触线的收缩速率为0.6617×10^(-5)cm/s。油砂洗油实验表明,改性片状纳米流体的洗油效率随油砂尺寸的增大和温度的提升逐渐增加,随着油砂浸泡时间的延长先急剧增加后缓慢上升,存在最佳浸泡时间(8±2)h,油砂洗油效率可高达95.7%。该项研究成果突破了只有高浓度球形纳米颗粒才能形成结构分离压力的限制,为片状纳米流体在矿场的应用提供了可能性,也为矿场施工工艺提供了技术参考。

渗吸置换提高原油采收率研究进展

渗吸置换作用已逐渐成为非常规油藏和低渗、特低渗裂缝性油藏提高原油采收率的一种重要方式,大量裂缝的存在及细小孔隙发育为渗吸作用的发生创造了有利条件。首先,基于毛细管压力与重力对渗吸的贡献程度,对渗吸模式进行分类;而后,主要聚焦于影响渗吸的各类因素,详细阐述如储层类型、孔渗物性、边界条件、流体(包括原油与渗吸液体)性质等因素对渗吸的影响规律及作用机制,总结了目前使用的研究渗吸的各种实验手段;最后,根据渗吸作用的研究进展,探讨在实验条件确定、黏土水化影响、界面张力优化和渗吸模式选择等方面所面临的问题,并对这些问题的研究前景进行展望。