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。     

鄂尔多斯盆地裂缝性低渗透油藏渗吸驱油研究

裂缝性低渗透油藏储层岩性致密,裂缝发育,非均质性强,注水开发效果差,利用水的自发渗吸作用驱油是一种经济有效的开发手段。文中利用鄂尔多斯盆地延长油田西区采油厂的天然露头岩心,通过自发渗吸实验,研究了边界条件、润湿性、温度、原油黏度、界面张力及渗透率等因素对渗吸驱油作用的影响。实验结果表明:润湿性、黏度、界面张力及渗透率是影响渗吸驱油的主要因素,岩石越亲水,原油黏度越低,渗吸驱油效果越好。对于亲水岩心,渗透率相近时,界面张力为0.04 m N/m时渗吸效果最佳;岩石渗透率差异明显时,渗透率为2.94×10~(-3)μm~2时渗吸效果最佳。实验结果为鄂尔多斯盆地裂缝性低渗透油藏渗吸驱油提供了重要的指导作用。     

Numerical Simulation of the LSWI Effect on Hydrocarbon Recovery From Carbonate Rocks

Wettability alteration mechanism is still believed to be the main contributor to low salinity water injection (LSWI) effect on oil recovery from carbonate rocks. The authors investigated the main mechanism and contributor to the LSWI effect on oil recovery from carbonate rocks through history matching recently published corefloods using the UTCHEM simulator. The history match results suggest that wettability alteration has negligible effect on water relative permeability, which could be related to the double electric layer expansion mechanism. This paper provides a basis to develop a LSWI model to predict oil recovery from carbonate rocks.     

束缚水饱和度、岩石性质对自吸的影响

自吸是裂缝性油藏采油的一个特别重要的方面。影响自吸的因素有很多,中主要研究束缚水饱和度和岩石性质自吸速度及采收率的影响。研究中使用的多孔介质分别为高渗砂岩、低渗砂岩、石灰岩。结果表明,束缚水饱和度对砂岩体系自吸速度有较强的影响。当束缚水饱和度Ｓｗｉ小于６％时,自吸速度随Ｓｗｉ增加而减小,在Ｓｗｉ为６％～１５％的范围内自吸速度达最低,当Ｓｗｉ在１５％～３０％的范围内,自吸速度随束缚水饱和度增高而升     

低盐度注水提高碳酸盐岩油藏采收率

碳酸盐岩油藏基质致密,且发育裂缝和溶洞,使得注水开发过程中含水率上升快、采收率低。 低盐 度注水是一项成本低廉、效果显著的注水提高采收率技术,始于 20 世纪 90 年代,近年来在国内外均受 到广泛关注。 梳理了碳酸盐岩油藏低盐度注水的增产机理、室内实验评价方法和矿场实施条件。 综合分 析指出,低盐度注水提高碳酸盐岩油藏采收率的主要机理是润湿性反转和孔喉连通性改善。 润湿性反 转由表面电荷改变或者矿物溶解引起,其实质是水相中的关键二价离子（SO₄^2-,Ca²⁺ ,Mg²⁺ ）与岩石表面发 生了化学反应;孔喉连通性改善主要由矿物溶解引起。 低盐度注水主要的室内实验评价方法有水驱实 验、自吸测试、表面张力测定、接触角测定、核磁共振、离子成分分析及 Zeta 电势测定等。 开展低盐度注 水能够有效降低注入压力,提高洗油效率,增加波及体积。 我国碳酸盐岩油藏分布广泛,开展低盐度注 水提高采收率技术的机理研究和应用研究,具有重大的现实意义。     

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.     

Wettability Alteration by Salinity and Calcium Bridge in a Crude Oil/Brine/Rock System

Wettability alteration has been considered to be a key factor behind low salinity water effect. Though the wettability alteration is widely accepted to be determined by oil components, mineral surfaces and ions in aqueous phase, how the brine chemistry (ionic type and strength) impacts the wettability is still unknown. In this study, the auhtors conducted spontaneous imbibition, contact angle, and zeta potential measurements to investigate: (a) how the ions of the thin film of water between oil and mineral interact with oil and rock to alter the wettability of crude oil/brine/rock system and (b) the mechanism of wettability alteration behind low salinity water effect.     

Wettability Modification of Fractured Carbonates Using Sodium Metaborate,Part I: Laboratory Results and Simulation Procedure

Abstract

Chemical-based wettability modification has become important for the worldwide abundance of fractured carbonates with the potential to enhance water imbibition to expel more oil from matrix to the fractures. The authors present systematic experimental and modeling approach on the combined benefit of wettability alteration for enhanced water imbibition and interfacial tension reduction. Brine, alkali, and alkali surfactant solutions were injected sequentially to improve oil recovery from a fractured mix-wet carbonate core. The experiments were successfully modeled with a simulator capable of modeling wettability alteration. Part I presents the experimental procedure and the results. The history match of the waterflood is also presented. In another article the authors describe the procedure to model alkali and alkali surfactant floods including sensitivity simulations of some key parameters.     

New approach for reservoir assessment using geochemical analysis: Case study

Spontaneous imbibition is an important IOR process, especially for fractured carbonate reservoirs with low permeability matrix blocks. If the chalk is oil-wet, the process will not take place. Previous studies have shown that seawater may increase the water-wetness. The sulphate ions in seawater may alter the wetting conditions of the chalk surface, especially at high temperatures.One-dimensional imbibition tests of water into vertically placed, preferentially oil-wet chalk cores were performed, with non-sulphate formation water as a reference. The cores were sealed and only open to flow at one or both end faces. For core plugs with both ends open, a delay period was observed if the core initially was 100% oil saturated, and the difference in oil recovery from top and bottom was about 2–4% of OOIP. For core plugs with initial water saturation, the difference was increased to 14% of OOIP with higher oil production from the top. For cores with only the upper end face open to flow, only countercurrent imbibition takes place. Higher oil recovery was observed with seawater than with formation water as imbibing brine. Cleaned core plugs can be more easily rendered partially oil-wet. A numerical model was developed to describe the seawater imbibition process, including the effect of wettability alteration, and used to simulate the experiments. The model includes molecular diffusion and adsorption of salts (sulphate), and gravitational and capillary forces. The salts in the seawater diffuse into the formation water initially present in the core, absorb onto the rock surface and induce wettability alteration.Two measured capillary pressure curves are used in the simulation. The curve with seawater is taken as the water-wet extreme, and the curve with non-sulphate formation water is taken as the oil-wet extreme. The capillary pressure curve is dynamically shifted from oil-wet to water-wet conditions proportionally to the absorb amount of salt. The simulation results match the experimental data well. The inclusion of the dynamic shift of the wettability condition controlled by molecular diffusion results in delayed oil recovery, in line with the experimental results.The model can easily be extended to include different types of ion concentration, e.g. of magnesium and calcium, to include more of the chemical reactions taking place.     

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。     

Enhanced gas-condensate production by wettability alteration to gas wetness

Many gas-condensate reservoirs experience a sharp drop in gas production due to condensation near the wellbore as pressure drops lower than the dew point. Wettability alteration approach has been demonstrated successful in laboratory. However few experiments have been conducted in real reservoir rock with a low permeability. The gas-condensate reservoirs impaired by condensation near the wellbore usually have low permeabilities. In this study, we conducted experiments in the rock sampled from the target gas field (Dongpu). Firstly a new and cheaper chemical was developed to change the rock wettability from preferential water- to gas-wetness effectively. This chemical was thermally stable at a temperature of 170 °C. Experimental results also showed that this chemical was effective at very high salinity. Secondly spontaneous water imbibition tests were run to show the effect of wettability alteration on recovery. Thirdly relative permeability data of gas and water were measured with and without wettability alteration to preferential gas-wetness. Experimental results demonstrated that the relative permeabilities of both the gas and the water phases were increased significantly after the wettability alteration to preferential gas-wetness. The residual water saturation was decreased and the gas production was enhanced greatly due to the wettability alteration.     

Effect of acid number of crude oil on oil recovery of smart water coupled with silica nanoparticles

Spontaneous imbibition (SI) is one of the most important mechanisms in reservoir engineering. In order to activate of this mechanism completely in carbonate reservoirs, wettability of these oil wet rocks should be altered to water-wet. Multi-step spontaneous imbibition tests were designed and conducted in this study. Results indicated that mixture of smart water and nano silica could increase oil recovery up to 5 percent. Effect of acid number of crude oil on oil recovery of this mixture was investigated by using three samples of crude oil during SI tests: A (0.38 mg KOH/g), B (0.25 mg KOH/g) and C (0.18 mg KOH/g). Maximum oil recovery of SI tests was recorded for oil sample C which had lowest acid number. Ion analysis of imbibing fluids indicated sharp reductions in concentration of sulfate ion in each step of SI tests which confirmed occurrence of ion exchange mechanism in the rock surface of core samples.     

微观孔隙结构对致密砂岩渗吸影响的试验研究

目前对于渗吸的研究多集中于润湿性和界面张力,微观孔隙结构作为影响自发渗吸的主要因素之一常被忽略。利用核磁共振技术对致密砂岩渗吸过程中的油水分布变化进行了研究,同时采用恒速压汞、氮气吸附、高压压汞等试验手段求取了平均孔喉比、比表面、孔隙尺寸等表征微观孔隙特征的参数,并在此基础上分析研究了微观孔隙结构对渗吸的影响。试验结果表明:在致密砂岩渗吸过程中,中等尺寸的孔隙采出程度最大;孔隙度与渗吸采收率相关性不大,而渗透率越大,储层品质越好,渗吸采收率越高;平均孔喉比和比表面均与渗吸采收率负相关,比表面越大,中小喉道分布越多,孔喉比越大,越不利于渗吸流体的吸入和非润湿相的排出;中等孔隙比例越大,渗吸采收率越高,而由于黏滞力的作用部分小孔隙无法进行有效的渗吸,小孔隙比例增大对于渗吸采收率的提高不利。因此,储渗性能较好、中等孔隙占比较高的致密砂岩储层更适宜采用渗吸采油。      

Wettability Alteration of Low-permeable Carbonate Reservoir Rocks in Presence of Mixed Ionic Surfactants

Abstract

Altering the wettability of the carbonate reservoir rocks from oil-wet to water-wet has figured prominently as one of the enhanced oil recovery methods in recent years. The authors measured the effect of different ionic surfactants on the wettability alteration of the rock, saturated with crude oil, and the consequent improvement in oil production was investigated by spontaneous imbibitions of solutions containing cationic, anionic, and cationic-anionic surfactant mixtures. A very low-permeable carbonate rock from one of the Iranian oil reservoirs was selected for this study. The results of imbibition tests were furthermore supported by measuring IFT, taking pictures of producing oil drops from different exterior core plug surfaces and also observing the distribution of the remaining oil in cores at the end of experiments. The results show that cationic surfactants at concentrations higher than CMC can cause a remarkable oil production through alteration of wettability and, moreover, the extent of oil production increases with temperature. In contrast, it is observed that the anionic surfactants are not able to change the wettability of an oil-wet surface and their combination with the cationic type would reduce the oil production potential of cationic surfactants.     

Effect of shape factor, characteristic length, and boundary conditions on spontaneous imbibition

Spontaneous imbibition is vital for oil recovery in porous media, especially when considering fluid flow behavior in fractured reservoirs. Small-scale laboratory tests on reservoir rock samples show that spontaneous imbibition becomes crucial in estimating field behavior according to oil recovery by imbibition performance. This paper presents experimental work on oil recovery by spontaneous water imbibition on kerosene/brine/Berea systems. The main objectives of this study were to investigate the effect of shape factor (SF), characteristic length (CL), and boundary conditions (BC) on the rate of spontaneous imbibition, and improve oil production simulation by spontaneous imbibition from naturally fractured reservoirs using derived shape factors. General mathematical definitions for shape factor and characteristic length are typically derived using irregular geometric shapes, but this investigation utilized regular geometric shapes of core samples (i.e., cylindrical, square prism, and triangular prism) for simplicity. Experiments were conducted on different sizes of core samples with cylindrical shapes yielding the highest imbibition rates and triangular prisms the lowest imbibition rates. Characteristic length had an inverse effect on the rate of spontaneous imbibition within the same shape family of core samples. Boundary condition (BC) experiments were performed to investigate the effect of the boundary on the rate of spontaneous imbibition. The four different boundary conditions applied to the samples were (1) all faces open (AFO), (2) two ends closed (TEC), (3) two ends open (TEO), and (4) one end open (OEO) systems. BC experiments showed that an increase in total surface area open to imbibition promoted the rate of spontaneous imbibition. In this study, kerosene/brine/Berea systems showed that imbibition recovery rates increase with an increase in shape factor while decreasing in characteristic length specific to the same shape of core samples.     

Effect of wettability on oil recovery and breakthrough time for immiscible gas flooding

The effect of wettability on oil recovery at higher water saturation is still not fully understood, especially in the case of mixed wettability. This study was conducted to examine the effects of wettability on oil recovery and breakthrough time through experiments for two wettability conditions (water-wet and mixed-wet) and three water saturations (20%, 40%, and 60%). Clashach sandstone core with a porosity of 12.8% and a permeability of 75 md was utilized as the porous media. Immiscible gas flooding was performed by injecting nitrogen gas into the core at room temperature and pressure. The results showed 54.3% and 48.8% of the initial oil in place (IOIP) as the ultimate oil recovery at 40% water saturation from mixed-wet core and water-wet core respectively. In contrast, the water-wet core displayed better results (32.6% of the IOIP) in terms of breakthrough time compared to the results of water-wet core (10.6% of the IOIP) at the same water saturation. In conclusion, oil recovery was found highly dependent on water saturation while breakthrough time was mainly affected by the wettability of the cores.     

Effects of low-salinity water coupled with silica nanoparticles on wettability alteration of dolomite at reservoir temperature

Wettability alteration in porous media is one of the mechanisms for enhancing oil recovery through injecting low-salinity water into carbonate reservoirs, in which active ions can remove the carboxylic oil component from the rock surface, altering the rock's wettability toward a water-wet condition. This study investigated the concomitant effects of low-salinity water and hydrophilic SiO₂ nanoparticles on oil-wet dolomite rock. Results revealed that low-salinity water coupled with hydrophilic nano-SiO₂ in oil-wet dolomite rock remarkably affected the wettability alteration of the rock, showing that the simultaneous presence of ions in water and hydrophilic nano-SiO₂ led to considerable wettability alteration compared with using just low-salinity water.     

The Influence of Surfactant Solution Injection in Oil Recovery by Spontaneous Imbibition

Imbibition is the spontaneous displacement of fluids through porous media that occurs until capillary equilibrium is reached. Factors such as wettability and high interfacial tensions may negatively affect the process, requiring additional work to enhance oil recovery. This work aims to explain some aspects of the dynamics of oil recovery by spontaneous imbibition using different fluids. Static imbibition and contact angle experiments were performed using sandstones of the Botucatu Formation (Brazil). The plug samples were exposed to immersion in brine and in surfactant solutions, and the progression of oil recovery was monitored with time. The results showed that the capillary imbibition rate and the oil recovery factor were higher when an ionic surfactant was used. The inverse Bond number and the shape of the recovery profile showed different trends of the capillary imbibition dynamics. Higher oil recovery factors for ionic surfactant were also an effect of the contact angles observed.     

压裂液存留液对致密油储层渗吸替油效果的影响

统计长庆油田罗*区块2015年存地液量与油井一年累积产量的关系发现,存地液量越大,一年累积产量越高,与常规的返排率越高产量越高概念恰恰相反,可能与存地液的自发渗吸替油有关。核磁实验结果表明,渗吸替油不同于驱替作用,渗吸过程中小孔隙对采出程度贡献大,而驱替过程中大孔隙对采出程度贡献大,但从现场致密储层岩心孔隙度来看,储层驱替效果明显弱于渗吸效果。通过实验研究了影响自发渗吸效率因素,探索影响压裂液油水置换的关键影响因素,得出了最佳渗吸采出率及最大渗吸速度现场参数。结果表明,各参数对渗吸速度的影响顺序为:界面张力 > 渗透率 > 原油黏度 > 矿化度,岩心渗透率越大,渗吸采收率越大,但是增幅逐渐减小;原油黏度越小,渗吸采收率越大;渗吸液矿化度越大,渗吸采收率越大;当渗吸液中助排剂浓度在0.005%~5%,即界面张力在0.316~10.815 mN/m范围内时,浓度为0.5%（界面张力为0.869 mN/m）的渗吸液可以使渗吸采收率达到最大。静态渗吸结果表明:并不是界面张力越低,采收率越高,而是存在某一最佳界面张力,使地层中被绕流油的数量减少,渗吸采收率达到最高,为油田提高致密储层采收率提供实验指导。      

裂缝性油藏低渗透岩心自发渗吸实验研究

裂缝性低渗透油藏注水开发时,注入水沿裂缝窜流,油井含水率高,地下注水波及效果差,油层水淹后仍有大量原油滞留在基质岩块中.渗吸排油是裂缝性低渗透油藏重要的采油机理,为研究各种因素对渗吸效果的影响,采用胜利油区纯梁采油厂天然低渗透岩心,通过在地层水和表面活性剂溶液中的自发渗吸实验,研究了润湿性、温度、粘度、界面张力等因素对渗吸的影响规律.实验结果表明:温度不是影响渗吸的直接因素,而是通过改变模拟油的粘度来间接影响渗吸;润湿性、模拟油粘度以及界面张力是影响自发渗吸的主要因素,岩石越亲水,模拟油粘度越低,渗吸采收率越高;对于亲水岩心,渗透率和界面张力控制着渗吸发生的方式;不同渗透率级别对应一个最佳的界面张力范围,在该范围内,渗吸的采收率最高;对于亲水—弱亲水岩心,岩心渗透率越大,所对应的最佳界面张力越低.