Low-salinity-based enhanced oil recovery literature review and associated screening criteria

A thorough literature review is conducted that pertains to low-salinity-based enhanced oil recovery(EOR).This is meant to be a comprehensive review of all the refereed published papers,conference papers,master’s theses and other reports in this area.The review is specifically focused on establishing various relations/characteristics or"screening criteria"such as:(1)classification/grouping of clays that have shown or are amenable to low-salinity benefits;(2)clay types vs.range of residual oil saturations;(3)API gravity and down hole oil viscosity range that is amenable for low salinity;(4)salinity range for EOR benefits;(5)pore sizes,porosity,absolute permeability and wettability range for low-salinity EOR;(6)continuous low-salinity injection vs.slug-wise injection;(7)grouping of possible low-salinity mechanisms;(8)contradictions or similarities between laboratory experiments and field evidence;and(9)compositional variations in tested low-salinity waters.A proposed screening criterion for low-salinity waterflooding is introduced.It can be concluded that either one or more of these mechanisms,or a combination thereof,may be the case-specific mechanism,i.e.,depending on the particular oil–brine–rock(OBR)system rather than something that is"universal"or universally applicable.Therefore,every OBR system that is unique or specific ought to be individually investigated to determine the benefits(if any)of low-salinity water injection;however,the proposed screening criteria may help in narrowing down some of the dominant responsible mechanisms.Although this review primarily focuses on sandstones,given the prominence of carbonates containing^60%of the world’s oil reserves,a summary of possible mechanisms and screening criteria,pertaining to low-salinity waterflooding,for carbonates is also included.Finally,the enhancement of polymer flooding by using low-salinity water as a makeup water to further decrease the residual oil saturation is also discussed.

低盐水驱对中低渗砂岩采收率及润湿性影响

低盐水驱是一项前沿的改善水驱技术,具有成本低、环境友好等优点。大庆油田中、低渗储层物性较差,化学驱效果不理想,而低盐水驱在中、低渗储层应用前景良好。分别选大庆油田中、低渗透率岩心各5块,采用矿化度为1 000~10 000 mg·L^(-1)盐水开展岩心驱替实验和接触角测试。结果表明:当注入水矿化度由10 000 mg·L^(-1)降为5 000 mg·L^(-1)时,采收率增加,等渗点右移,含油饱和度下降,储层变为水湿;当注入水矿化度从5 000 mg·L^(-1)降为1 000 mg·L^(-1)时,采收率下降,等渗点左移,驱替压力上升,引发黏土膨胀,含油饱和度上升,储层为中性润湿。因此,利用低盐水驱开发大庆油田中、低渗油藏可行,能够提高原油采收率,并改善注入能力,并且矿化度阈值为5 000 mg·L^(-1)。

Effect of water salinity on oil/brine interfacial behaviour during low salinity waterflooding: A mechanistic study

In recent years,controlling the salinity and composition of the injected water has become an emerging enhanced oil recovery(EOR)technique,often described as low salinity(LS)waterflooding.This work is done with the intention to contribute to the ongoing discussions about LS waterflooding mechanism(s).For this purpose,a series of different experiments were conducted.At first,the effect of salinity on the interfacial tension(IFT)and the contact angle was evaluated with a crude oil sample.Then to achieve more accurate results in observing oil/water interface,similar IFT experiments were also carried out on a synthetic oil containing asphaltenes.Thereafter,microscopic visualization using glass micromodel was performed on the interface of the synthetic oil sample and brines.Four brine solutions including Sea Water(SW),it's dilutions and formation water(FW)were used for various experiments.Finally,to investigate the presented mechanism by other authors,a series of Environmental Scanning Electron Microscopy(ESEM)analysis on the synthetic oil was carried out to understand better the phase behaviour after contacting both synthetic oil and water phases from the micromodel experiment.Based on the existing mechanism,there exists an optimal concentration beyond which dilution is no longer an effective process.

Addition of surfactants to Low Salinity Waterflooding in microfluidics system to increase oil recovery

This study was conducted to investigate the phenomenon of oil removal from inside pores using a self-designed microfluidic test kit.An artificial micromodel chip as a representation of porous rocks has been created with a uniform pore structure design and made of PMMA(Polymethyl Methacrylate)material.The micromodel chip has a porosity of 27.8%as well as a permeability of 2.7 Darcy.By using the microfluidic test kit,this study has investigated how low salinity water(LSW)injection with MgCl_(2)divalent ions and the addition of anionic surfactant,linear alkylbenzene sulfonate mixed with nonionic surfactants,nonylphenol ethoxylate(NP-10)affects to oil recovery.The injection of LSW and surfactant solution was carried out with different injection stages,injection rates and surfactant solutions con-centrations.Visual images during the injection process are recorded for analysis,which is the advantage of dynamic testing using this microfluidic test kit over conventional coreflooding.From this study,it is indicated that the selection of ions contained in LSW affects the success of LSW injection.Reducing the surfactant injection rate from 50 mL/min to 20 mL/min can increase the oil recovery from 1.27%to 4.29%.Oil recovery was also higher on surfactant injection which resulted in lower interfacial tension of the system based on the calculation of interfacial tension obtained from the Chun-Huh and Ghosh equations from the Winsor test.From all injection scenarios carried out in this study,the highest increase in oil recovery of 26.87%OOIP was obtained by injecting surfactant solutions directly in the secondary stage without prior LSW injection.

基于DLVO理论的低矿化度水驱对岩石润湿性的影响

为明确润湿性改变机制的主控因素,基于胶体稳定性(DLVO)理论和扩散双电层理论,建立表征岩石-水膜-原油系统界面间相互作用的分离压力数学模型,从微观受力角度对水驱矿化度与离子价型等分离压力影响因素进行敏感性分析;结合Young-Laplace方程和相互作用势能理论,计算不同水驱矿化度与离子价型下的稳定水膜厚度和岩石润湿角。结果表明:水驱离子价型是影响岩石润湿性的主控因素,少量二价阳离子即可产生极负的分离压力,形成厚度为0.375 nm的较薄水膜,水相润湿角维持在约20°;采用一价阳离子水驱时,随着矿化度的降低,分离压力逐渐增大并产生较高的正峰值,形成厚度为5.334 nm的较厚水膜,岩石润湿性转变为完全水湿(水相润湿角为0°),原油最终脱离岩石表面;在油田注水开发过程中,采用一价阳离子的低矿化度水驱在提高采收率上具有更高的潜能。

黏土矿物类型对低矿化度水驱采收率的影响实验

为定量表征不同黏土矿物对低矿化度水驱效果影响程度,分析低矿化度水驱的作用机理,采用黏土悬浮液对石英颗粒表面的高温黏附技术,制作了石英颗粒表面附着不同黏土矿物的填砂模型,并开展了岩心驱替实验和Zeta电位、接触角测试实验。结果表明:低矿化度水驱对纯石英砂填砂模型提高采收率效果不明显,黏土矿物的存在是低矿化度水驱提高采收率的必要条件;附着高岭石的石英砂模型的水驱采收率随注入水矿化度的降低呈提高趋势,附着蒙脱石的石英砂模型的水驱采收率在初期也随矿化度降低而逐渐升高,但存在一个最高采收率的临界矿化度,其后随注入水矿化度的进一步降低,最终采收率又呈现降低趋势;而蒙脱石黏土遇低矿化度水后,会使附着原油的蒙脱石颗粒膨胀运移而提高洗油效率,但随着离子质量浓度的降低,脱落的微粒增多,堵塞渗流通道,又会影响水驱效果;附着混合黏土岩心和附着蒙脱石岩心具有相似的水驱采收率变化规律,附着混合黏土的岩心模型的水驱效果要好于附着单一黏土矿物的岩心模型。

碳酸盐岩油藏低矿化度水驱作用机理实验

碳酸盐岩油藏低矿化度水驱应用潜力巨大,为了更好地推广其矿场应用而针对性开展作用机理的实验研究。首先,岩心驱替实验研究注入水矿化度和关键离子组成对采收率的影响;而后,润湿角测定实验分析注入水矿化度和关键离子组成对碳酸盐岩表面润湿性的影响;最终,根据实验结果建立碳酸盐岩油藏低矿化度水驱作用机理。研究发现:低矿化度水驱能有效改变碳酸盐岩表面润湿性进而提高油藏采收率,存在最优矿化度使得碳酸盐岩表面润湿性变化最大、采收率最高;Mg^2+和SO4^2-对碳酸盐岩表面润湿性和原油采收率的影响效果不同;随着溶液中Mg^2+浓度升高,碳酸盐岩表面润湿性变化不断增强、原油采收率不断升高;随着溶液中SO4^2-浓度增加,碳酸盐岩表面润湿性变化先增强后减弱、原油采收率先增加后稳定。碳酸盐岩油藏低矿化度水驱作用机理在于润湿性的改变:①SO4^2-吸附在正电性的碳酸盐岩矿物表面,中和表面电荷,促进了Mg^2+向矿物表面运动;②Mg^2+与碳酸盐岩矿物表面的Ca2+发生取代反应,造成原油组分的解离。

二价阳离子在低盐水改变砂岩润湿性中的作用

根据岩心自渗吸实验及Zeta电位测试结果,在宏观上研究二价阳离子改变砂岩表面润湿性的机理;根据极性模拟油组分在砂岩表面吸/脱附实验和分子模拟结果,在微观上阐释二价阳离子改变砂岩表面润湿性的机理。结果表明:原油中的酸性组分和砂岩表面硅醇基团被电离而带负电,酸性组分主要通过二价阳离子架桥吸附于砂岩表面,并不能通过一价阳离子架桥吸附及范德华力吸附,砂岩表面亲水性减弱;盐水盐度降低使酸性组分、砂岩表面负电性增强,两者静电斥力增大,酸性组分脱附,导致砂岩表面亲水性增强。

水驱油藏特高含水阶段提高采收率可行性研究及技术对策

常规砂岩油田注水开发最终采收率多为35%~50%。基于大量室内实验、应用实例和中外油田案例类比,分析了特高含水开发阶段进一步提高水驱油藏驱油效率的可行性。讨论了水驱油藏在周期注水、关停老井侧钻、多油层逐层上返或沿断层面钻加密井等扩大注水波及体积基础上,长期高孔隙体积倍数注水、低矿化度水驱等经济可行的提高驱油效率思路和方法。室内研究和矿场实践结果表明,长期注水开发砂岩油藏润湿性由偏亲油性向偏亲水性转化,残余油饱和度降低,有利于提高驱油效率。依据成熟开发油田大量类比实例,在油层和流体性质较为有利的条件下,强天然水驱油藏依靠天然能量开采,或弱天然能量油藏通过注水开发最终采收率可达70%。采用自流水注水、低矿化度水驱、同井注采工艺等技术已证实是经济可行的。特高含水开发阶段老油田已有的大量开发井和配套设施为进一步提高采收率提供了基础。应用经济可行的长期高孔隙体积倍数注水思路有望将水驱开发油田采收率进一步提高至50%~70%。

鄂尔多斯盆地延长组致密砂岩油藏低盐度水驱作用规律

目前低盐度水驱研究主要集中于中高渗透、高黏土质量浓度的砂岩油藏,是否适用于致密砂岩油藏有待于深入研究。基于这种情况,以鄂尔多斯盆地致密油藏岩心和原油为研究对象,利用岩心驱替实验、润湿角测定实验、界面张力以及界面扩张流变测定实验开展致密砂岩油藏低盐度水驱作用规律研究。实验结果表明:低盐度水驱适用于致密砂岩油藏,调整注入水离子组成改变岩石表面润湿性以及油水相互作用,即可实现采收率的提高;其中,降低Ca^(2+)质量浓度或增加SO_(2)质量浓度可促进极性原油组分脱离岩石表面,增强岩石表面水湿性;与此同时,降低Ca^(2+)质量浓度或增加SO_(2)质量浓度可促进极性原油组分在油水界面的吸附,降低界面张力并增强界面黏弹性;降低Ca^(2+)质量浓度或增加SO_(2)质量浓度对提高采收率有较好效果。研究成果为低盐度水驱在致密砂岩油藏中的应用提供了理论参考。

纳米SiO_(2)膨胀驱油剂提高采收率

渗透压作为低矿化度水驱提高采收率新机理近年来得到了广泛研究,注入水中水分子在渗透压作用驱动下进入被油滴包裹的水滴中,使原油发生表观膨胀现象.但目前仅靠渗透压作用对原油膨胀的效果不明显,且对于原油膨胀的研究仅限于定性研究,缺乏定量分析.本研究引入3种纳米SiO_(2)作为原油膨胀强化驱油剂,以油包水(W/O)乳状液模拟油藏中原始油水分布,观察W/O乳状液液滴的膨胀效果,并计算膨胀倍数.实验结果表明:亲水和疏水纳米SiO_(2)均能起到强化原油膨胀的效果,且由于亲水硅溶胶(HS-40)具有更小的粒径和较高的Zeta电位绝对值,对原油的膨胀效果更好.随着HS-40质量分数增加,在吸附作用下,油水界面处的表面活性物质进入原油内部,加速原油膨胀;在HS-40质量分数为0.20%时原油膨胀倍数达到最高,为3.29倍;当HS-40质量分数继续增加,纳米SiO_(2)颗粒将阻碍水分子在油水界面处的传质.当地层水与注入水之间存在较大的矿化度差异时,纳米SiO_(2)的存在能加速原油表观膨胀现象,该现象为低矿化度水驱提供了一个新思路.

Impact of the injected water salinity on oil recovery from sandstone formations:Application in an Egyptian oil reservoir

In the last decade,there has been an increasing interest in understanding the effects of changing injected water salinity on the performance of oil reservoirs.This paper aims to investigate the effects of injected water salinity on oil recovery of an Egyptian oil reservoir(Bahariya formation).An experimental work program has been performed using 25 core plugs and 5 different water salinities to study the effects of changing water salinity during both secondary and tertiary stages of waterflooding.The objectives of the experimental work were to(1)investigate the effects of the low water salinity on oil recovery and(2)identify the optimum water salinity and the main reservoir parameters for application of low salinity waterflooding project(LSWF)in Bahariya formation.The results revealed that there is an optimum salinity for waterflooding in the secondary flooding stage.However,for the tertiary flooding stage,the results showed that the controlling factor is not decreasing the salinity,but rather changing the salinity(e.g.either increasing or decreasing).It was also clear that applying the optimum salinity in the secondary recovery stage is more effective than applying it in the tertiary recovery stage.Furthermore,the results showed that the positive impact of LSWF may be expected in reservoirs with high amount of kaolinite,high values of CEC,and low amounts of plagioclase feldspar.This study is an original contribution to develop guidelines for designing optimum salinity waterflooding projects in sandstone reservoirs.

Role of the injected water salinity and ion concentrations on the oil recovery in carbonate reservoirs

Low salinity water flooding(LSWF)was initially considered using water with a low concentration of dissolved salts and was later extended to include modifying the ionic content of injected brines.This work investigates the effects of changing water salinity and composition along with the concentration of sulfate and iodide ions on oil recovery in carbonate reservoirs during the tertiary recovery stage.An experimental study was carried out using crude oil of 29°API,8 core samples extracted from the Eocene carbonate reservoir(Egypt),and 6 different water salinities.The results showed additional oil recovery up to 5%of the original oil in place(OOIP)in the tertiary recovery stage with changing water salinity and water composition.Injection of high salinity(HS)and low salinity(LS)brines with high sulfate concentrations increased the incremental oil recovery by a value ranging from 1.7 to 3.8%of the OOIP.On the contrary,injection of HS and LS brines with low sulfate concentrations showed insignificant incremental oil recovery(less than 1%of the OOIP).Furthermore,injection of water with potassium iodide(KI)after injection of water with high sulfate brines showed additional oil recovery of about 1.7%of the OOIP.On the other hand,injection of water with KI after injection of water with low sulfate concentration showed insignificant incremental oil recovery(less than 0.4%of the OOIP).The concentration of sulfate in the injected water appeared to be key parameter to achieve effective waterflooding(WF)projects in carbonate reservoirs.Moreover,the results revealed that the multi-component ion exchange(MIE)mechanism seems to be the primary recovery mechanism for LSWF in carbonate reservoirs.The results and conclusions of this study can be used to develop guidelines for designing waterflooding projects in carbonate reservoirs with optimum salinity.

低矿化度水驱中的微粒运移机理及其开发效果

低矿化度水驱作为一种经济可行的精细化注水技术,其产生的微粒运移机理能有效地改变储层物性与吸水剖面,进而达到均衡驱替和提高采收率的效果.本文基于胶体稳定性Derjaguin-Landau-Verwey-Overbeek (DLVO)理论与扩散双电层理论,从微观角度分析了注入水矿化度、离子价型等因素对黏土微粒受力与运移量的影响,通过最大滞留体积分数方程建立了微粒运移量与渗透率损伤程度间的关系.针对纵向非均质油藏特高含水期层间干扰严重的问题,开展了特高含水期转注低矿化度水驱的数值模拟研究.微粒受力分析与数值模拟结果表明,特高含水期转注低矿化度水后,分流量较多的高渗层会产生大量的黏土微粒水化膨胀、运移与堵塞作用,造成高渗层渗透率明显下降,注入水被更多地分流到水驱程度较小的中、低渗层,有效地调节了吸水剖面并缓解了层间干扰问题,相比常规海水驱可提高约3%的原油采收率,进而达到提高层间均衡动用程度与原油采收率的效果.

Modern methods of underground hydromechanics with applications to reservoir engineering

In the report the basic principles of new approach to the study of transport processes in porous medium are represented. The ＂percolation＂ approach has arisen as an attempt to overcome the traditional phenomenological approach in the underground hydromechanics, based on the assumption of continuity of saturated porous media, which does not allow to explain and to model a number of effects arising from the fluids flow in porous media. The results obtained are very interesting not only from the scientific point of view but as the scientific basis for a number of enhanced oil recovery technologies.