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；Mg²⁺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Mg²⁺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Mg²⁺向矿物表面运动；②Mg²⁺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。     

低矿化度注水提高砂岩储集层采收率的微观机理

低矿化度注水是一项前沿技术,因在碳酸盐岩和砂岩储集层中能提高驱油效果,目前受到广泛关注。本文梳理了砂岩储层低矿化度注水提高采收率的主要微观机理,即润湿性的改变、黏土的膨胀与运移、双电层的扩散等。低矿化度水的质量浓度、离子类型能改变多种黏土内部力平衡及黏土与原油之间的力平衡,造成双电层扩散,最终使黏土出现润湿性的改变以及膨胀运移的现象。低矿化度注水能提高大部分砂岩油藏的采收率。国内大部分砂岩油藏开发已进入中后期,进行低矿化度注水的微观机理研究对砂岩油藏开发有极大的指导意义。     

低矿化度水驱提高原油采收率研究进展

低矿化度水驱是指向地层中注入矿化度为1～5 g/L 的水来提高采收率。目前,关于低矿化度水驱提高原油采收率的机理仍存在争议。通过梳理低矿化度水驱技术的发展历程,总结了砂岩油藏低矿化度水驱提高采收率的机理大致可分为微粒运移和润湿性改变两大方面。简述了碳酸盐岩油藏低矿化度水驱提高采收率的机理,主要包括由于矿物溶解引起的双电层的变化和离子反应。浅析了适用低矿化度水驱技术的油藏条件,总结了低矿化度水驱和其他驱油工艺结合的新技术,介绍了分子模拟技术在低矿化度水驱方面的应用,并对未来的发展提出了建议。     

基于井间连通性的碳酸盐岩油藏注采关系优化

碳酸盐岩油藏储集层非均质性强,注水开发时注入水易沿高渗通道窜进,导致生产井发生水窜或水淹、含水率上升速度加快、开发效率低。基于井间连通性原理,根据缝洞型碳酸盐岩油藏的地质特征、开发动态等,可定量表征井间的连通性参数传导率和连通体积,构建碳酸盐岩纵向多层油藏井间连通性模型,进而获取油藏各层注水井平面注水劈分系数、注水利用率等。结合自动历史拟合方法和生产优化算法,实现对油水井生产动态的实时优化和预测。现场应用表明,该方法年增油1.1×10⁴ m³,具有较好的增油效果,对同类型油藏的高效开发有重要指导意义。     

离子组成及矿化度对低矿化度水驱采收率的影响

低矿化度水驱提高采收率对注入水和地层水的离子组成有一定的要求。在室内砂岩岩心驱替实验的基础上,采用对比的方法,研究了注入水和地层水的离子组成对低矿化度水驱提高采收率的影响。结果表明：在进行三次采油模式下的低矿化度水驱时,地层水中含有二价阳离子Ca²⁺或Mg²⁺均可提高采收率,且Ca²⁺的效果要好于Mg²⁺;只有注入水的矿化度低于油藏油水系统低矿化度效应启动阈值时,采收率才会提高。分析实验结果确定,地层水中含有二价阳离子Ca²⁺或Mg²⁺,以及注入水的矿化度低于由油藏油水系统决定的矿化度阈值,是实现低矿化度水驱提高采收率的必要条件。     

高邮凹陷高含水砂岩油藏储层物性变化特征及影响因素分析

高含水砂岩油藏经过长期注水后,其物性会发生变化,对油藏开发产生明显的影响。为此,通过利用不同渗透率的岩心开展了水冲刷实验研究,并在实验基础上分析了黏土矿物、孔喉特征及岩石润湿性等对储层物性变化的影响。实验结果表明,渗透率较大的样品随着注水倍数的增加,渗透率逐渐增大;渗透率较小的样品随着注入倍数的增加,渗透率逐渐减小;且不同注入速度会影响物性的最后变化程度;黏土矿物含量、孔喉特征和岩石润湿性三者对储层物性变化有影响,其中黏土矿物含量对物性变化影响最大,孔喉特征和岩石润湿性影响较小。     

注气驱油技术发展现状与启示

我国注气驱油提高采收率技术发展较晚,且存在注CO₂与氮气谁更优的争议。根据国内外１０ a来注气开采发展的相关数据,从储层岩性、储层渗透率、储层深度、温度、原油饱和度、黏度等方面分析了国内外注气技术的发展状况。分析结果表明：发展注CO₂提高采收率技术具有广阔的应用前景;受温室气体减排的影响,国际上注CO₂驱油项目主要以注气混相驱发展最快,而我国注气试验主要采用商品CO₂气,并且存在混相困难的问题;碳酸盐岩油藏注气项目超过砂岩油藏,而传统认为碳酸盐岩油藏具有裂缝,注气要窜,故不适合注气开采;国际上在砂岩油藏注气开采的渗透率并不是太低（大于10×１０^-3 μm^２）,而我国注气试验都是超低渗透率（小于10×１０^-3 μm^２）;多数油藏是在注水后再进行注气,而过去认为注水后对注气效果不利;国外注空气目前主要采用高温氧化开采轻油,而不是稠油,而传统认为热采适合于稠油。针对我国目前注气情况和国外发展趋势,就如何开展注气驱油工作提出了建议。     

低渗透油藏精细水驱提效再认识

低渗透油藏储层岩性致密,具有孔喉细、压力系数低、裂缝发育等特点。注水开发单井产量低、产量递减快,稳产基础薄弱;储层非均质严重,动用程度和驱替程度较低;易水淹水窜,采油速度及采收率难以提高。为了克服这些问题,持续攻关形成了精细油藏刻画技术,配套精细分层注水工艺,在低渗透油藏开发中成功应用。油藏精细描述是实施精细水驱的基础,主要包括单砂体精细刻画、裂缝精细表征、储层微观孔隙结构精细刻画等技术。精细水驱包括井网加密调整技术、精细分层注水技术、智能分层注水技术、纳米微球调驱技术、温和超前注水技术等,可解决低渗透油藏注水开发水平及垂向注采不平衡的矛盾,有效提高采收率。温和超前注水技术对克服裂缝开启、地层破裂、启动压力梯度三者间的矛盾具有重要意义,使地层压力维持在相对平均的稳定状态,有利于延长油田稳产期。相对于常规水驱,精细水驱技术预期提高低渗透油藏采收率5%以上。     

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%。     

辽河油田高3618区块火线预测及注采参数优化

辽河油田高升稠油油藏高3618区块受储集层强非均质性、井间干扰、孔喉堵塞等影响,火线推进不均匀,火驱效益低,为此,通过火驱物理模拟实验,明确原油不同氧化阶段的温度界限,利用阿伦尼乌斯方程修正动力学参数,在基础井网上建立井间连通性模型,定量表征注采井间连通程度。并用高温气体示踪剂模拟方法验证连通性模型合理性,两者结合表征火线的运移轨迹,拟合精度提高到85%。通过数值模拟方法优化注采参数来调控火线,减缓气窜,增大了火驱波及系数,提高了原油采收率。如I5-0151C2井与I51-156井初始日注气量均为10 000 m³,I5-0158C井为10 500 m³,注气井月增注气量3 000 m³,水平井定液量100 m³ /d,参数优化后能够有效维持火线均匀推进,火驱波及系数扩大了8.74%,采收率提高了6.37%。     

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.     

Efficiency of enhanced oil recovery by injection of low-salinity water in barium-containing carbonate reservoirs

When low-salinity water containing sulfate ions is injected into carbonate reservoirs, rock dissolution and in situ precipitation occur, altering rock permeability and wettability. Particularly, when barium ions are present in formation water, they react chemically with \({\text{SO}}_{4}^{2 - }\), and BaSO₄ is precipitated. These reactions can cause a serious impact on the efficiency of enhanced oil recovery (EOR). Therefore, the main purpose of this study was to identify EOR efficiency induced by low-salinity waterflooding (LSWF) when Ba²⁺ is present in carbonate reservoirs. From the experimental results, it was confirmed that the permeability calculated by the measured pressure difference was improved because of rock dissolution predominating over in situ precipitation for the case of low Ba²⁺ concentrations. In the analysis of wettability alteration through the measurements of relative permeabilities before and after LSWF, the higher Ba²⁺ concentration case consumed more \({\text{SO}}_{4}^{2 - }\) in precipitating the BaSO₄, resulting in weaker wettability alteration due to the reduction of sulfate activity. These phenomena ultimately influenced EOR efficiency, i.e., the oil recovery was greater for the lower Ba²⁺ concentration.     

Experimental and modeling study of wettability alteration through seawater injection in limestone: a case study

Water flooding is widely applied for pressure maintenance or increasing the oil recovery of reservoirs. The heterogeneity and wettability of formation rocks strongly affect the oil recovery efficiency in carbonate reservoirs. During seawater injection in carbonate formations, the interactions between potential seawater ions and the carbonate rock at a high temperature can alter the wettability to a more water-wet condition. This paper studies the wettability of one of the Iranian carbonate reservoirs which has been under Persian Gulf seawater injection for more than 10 years. The wettability of the rock is determined by indirect contact angle measurement using Rise in Core technique. Further, the characterization of the rock surface is evaluated by molecular kinetic theory(MKT) modeling. The data obtained from experiments show that rocks are undergoing neutral wetting after the aging process. While the wettability of low permeable samples changes to be slightly water-wet,the wettability of the samples with higher permeability remains unchanged after soaking in seawater. Experimental data and MKT analysis indicate that wettability alteration of these carbonate rocks through prolonged seawater injection might be insignificant.     

致密油储层微观特征及其形成机理——以鄂尔多斯盆地长6-长7段为例

鄂尔多斯盆地陇东地区长（延长组）6段和长7段富含大量致密油,但由于对其微观特征与成因缺乏深入了解,阻碍了该区致密油的有效开采。为此,根据岩石孔隙铸体薄片、场发射扫描电镜等技术,对研究区长6段和长7段致密油储层微观特征及其成因进行了深入研究。结果表明：研究区致密油储层形成于三角洲前缘远端远砂坝-席状砂及半深湖-深湖重力流沉积环境,岩石粒度细（主要为极细砂岩、粉砂岩、泥质粉砂岩及粉砂质泥岩）、杂基含量高（8%~10%）,几种储集岩的孔隙均极不发育,面孔率低,平均1.8%,孔径小（平均30 μm）,喉道细（平均0.08 μm）,平均孔隙度9%,渗透率基本上都低于0.3×10^-3 μm²,物性差。孔隙类型主要为粒间杂基微孔、长石及岩屑溶孔、胶结物晶间微孔。不同岩石类型其微观特征存在差异。沉积环境决定了其粒度细、粘土杂基高,细粒高粘土杂基岩石抗压性差,强烈的压实作用导致大量的原生孔隙损失,孔喉变得更加细小;孔喉细小的岩石由于孔隙中各种流体离子的半渗透膜效应引起强烈的碳酸盐和粘土矿物胶结,尤其是伊利石搭桥状和丝网状胶结,使岩石孔隙度渗透率进一步变差,后期酸性流体也难以进入发生溶蚀作用;云母与水云母杂基及碳酸盐胶结物对石英的强烈交代导致岩石抗压性变差以及固体体积增加,最终导致岩石的致密化。     

鄂尔多斯盆地镇北地区长4+5储层微观孔隙结构研究

鄂尔多斯盆地镇北地区延长组长4+5以成岩型低渗透储层为主,常规方法较难评价该类储层微观孔隙结构品质。利用铸体薄片、扫描电镜和物性分析等方法对影响储层微观孔隙结构特征的因素进行了定性分析,恒速压汞方法对储层微观孔隙结构特征参数进行了定量表征。研究表明:镇北地区长4+5低渗透储层微观孔隙结构与成岩作用密切相关,主要表现为机械压实作用和碳酸盐胶结作用越弱,长石溶蚀作用越强烈,粒间孔和溶蚀孔越发育,孔喉连通性越好,渗透率越大;微观孔隙结构和渗透率受大于0.12μm的喉道控制明显,主要表现为平均喉道半径越大,渗透率越大,孔喉半径比越小,微观孔隙结构越好,储层品质因子越大,试油产液量越高,尤其当平均喉道半径小于1.60μm时。喉道是影响低渗透储层微观孔隙结构品质的主要因素。     

Enhanced oil recovery from carbonate reservoirs by spontaneous imbibition of low salinity water

An experimental study was performed to investigate the impact of low salinity water on wettability alteration in carbonate core samples from southern Iranian reservoirs by spontaneous imbibition. In this paper, the effect of temperature, salinity, permeability and connate water were investigated by comparing the produced hydrocarbon curves. Contact angle measurements were taken to confirm the alteration of surface wettability of porous media. Oil recovery was enhanced by increasing the dilution ratio of sea water, and there existed an optimum dilution ratio at which the highest oil recovery was achieved. In addition, temperature had a very significant impact on oil recovery from carbonate rocks. Furthermore, oil recovery from a spontaneous imbibition process was directly proportional to the permeability of the core samples. The presence of connate water saturation inside the porous media facilitated oil production significantly. Also, the oil recovery from porous media was highly dependent on ion repulsion/attraction activity of the rock surface which directly impacts on the wettability conditions. Finally, the highest ion attraction percentage was measured for sodium while there was no significant change in pH for all experiments.     

低矿化度水驱研究进展及展望

针对国外低矿化度水驱已运用于矿场实践而国内相关研究还未开展的现状,对低矿化度水驱机理 及其存在的问题进行了综述,并对低矿化度水驱的发展趋势作了展望。对于砂岩油藏,低矿化度水驱提高 采收率的机理主要为类碱驱、微粒运移以及多组分离子交换引起的储层润湿性改变;而对于碳酸盐岩油 藏,低矿化度水驱提高采收率的机理则主要是多组分离子交换引起的储层润湿性改变。原油性质、储层 性质、地层水及注入水性质、地层温度等因素均可以影响低矿化度水驱提高采收率的效果。目前低矿化度 水驱存在的问题主要包括提高采收率机理不清、低矿化度水源限制、油田储层适应性问题等。最后指出, 低矿化度水驱若与现有油田开发技术、煤层气生产技术、低渗透油田及高含水油田开发技术相结合,将会 是经济、环保、潜力巨大的提高采收率新技术。     

Recent advances in application of nanotechnology in chemical enhanced oil recovery: Effects of nanoparticles on wettability alteration,interfacial tension reduction,and flooding

Chemical methods of enhanced oil recovery (CEOR) are applied for improving oil recovery from different kinds of oil reservoirs due to their ability for modifying some crucial parameters in porous media, such as mobility ratio (M), wettability, spreading behavior of chemical solutions on rock surface and the interfacial tension (IFT) between water and oil. Few decades ago, the surfactant and polymer flooding were the most common CEOR methods have been applied for producing the remained hydrocarbon after primary and secondary recovery techniques. Recently, more attention has been focused on the potential applications of the nanotechnology in enhanced oil recovery (EOR). For this purpose, many studies reported that nanoparticles (NPs) have promising roles in CEOR processes due to their ability in changing oil recovery mechanisms and unlocking the trapped oil in the reservoir pore system. This paper presents a comprehensive and up-to-date review of the latest studies about various applications of nanoparticles (NPs) within the surfactant (S), polymer (P), surfactant-polymer (SP), alkaline-surfactant-polymer (ASP) and low salinity waterflooding processes, which exhibits the way for researchers who are interested in investigating this technology. The review covers the effects of nanoparticles on wettability alteration, interfacial tension reduction and oil recovery improvement, and discusses the factors affecting the rock/fluid interaction behavior in porous media through the nanofluid flooding.