Experimental Investigation of Contact Angles Under Oil-Microbial Solution on Carbonate Rocks

Contact angles are used to measure the wetting behavior of two immiscible fluids on a solid surface. Fluids are considered wettings if their contact angles with surface are less than 90°, and they are considered nonwetting, if their contact angles are greater than 90°. Because of its influence on other petrophysical properties of reservoir rocks, such as relative permeability, capillary pressure, and the residual oil saturation after a flood, wettability and its direct measure, the contact angle, play a significant role in affecting the recovery from both primary and improved recovery processes. In this work, contact angle alteration occurring in microbial enhanced oil recovery processes (MEOR) are quantified and described, along with a study of the factors that would enhance such contact angle alteration. An experimental method for the measurement of contact angles has been developed in which the contact angle is measured as a function of time. Measurements of contact angle and interfacial tension for four different types of UAE crude oil and four different mineralogical rock composition over a range of microbial concentration, salinity, and temperature are reported. Results showed that contact angles for the studied systems increased with temperature, crude oil sulfur concentration and microbial concentration up to a certain concentration, beyond which the bacteria concentration exhibited no effect on the contact angle. Crude oils containing low asphaltene concentration produced a stable contact angle and oils containing high asphaltene concentration produced surfaces with unstable wettability. The mineralogical composition of limestone rocks had no effect on the contact angle of microbial-oil system.     

原油沥青质在油藏岩石表面的吸附特性

选用两种原油沥青质样品，对沥青质在岩石孔隙表面的吸附及吸附所引起的润湿性变化进行了实验研究。对润湿性的测定结果表明，油藏岩石润湿性改变的程度主要取决于沥青质的来源和地层水的离子组成，同时也与离子浓度和岩样的束缚水饱和度有关。通过使用分光光度法测定沥青质在砂岩上的吸附量，初步建立了润湿指数（ＷＲ）与沥青质吸附量（ａ）之间的定量关系。对于某一给定的原油沥青质，ＷＲ值随ａ值增加而趋于降低。图４表３参１０（邓春萍摘     

无机盐与沥青质的协同作用对油藏润湿性的影响

选用两种原油沥青质样品,对沥青质在岩石孔隙表面吸附所引起的润湿性改变进行了实验研究。测定结果表明,岩样润湿性改变的程度主要与沥青质的来源和岩样所含盐水的组成有关。盐水中无机阳离子的类型对沥青质所引起的油藏岩石润湿性改变有十分重要的作用。在浓度相同的情况下,阳离子价数越高,对润湿性的影响越大。盐水中的无机阴离子对沥青质引起的润湿性改变影响很小。在油气开采过程中,地层水和注入水的离子组成,特别是所含阳离子的类型,是影响油藏岩石润湿状态的一个不可忽视的因素。     

声波振动与岩石表面润湿性

通过水与岩石表面接触角的测定、声被驱油实验和理论分析,研究考察了声波振动对原油─岩石、水─岩石界面特性的影响,从界面化学角度对岩石表面的润湿性和声波驱油机理进行了探索。结果表明:经原油浸泡后,由于原油中极性化合物(胶质、沥青质等)在岩石表面的吸附,岩石表面由水相润湿为主转变为油相润湿为主;无论岩石表面以水相润湿为主还是油相润湿为主,在水浸泡过程中,声波振动可促进其表面亲油性减弱和亲水性增强,毛细管阻力降低;伴随着岩石表面润湿性的改变,原油对岩石表面的粘附功明显降低;减弱了原油与岩石表面间的粘滞力,使原油更易于从岩石表面上剥离,提高原油采收率;岩石的渗透率越低,声波振动作用越显着。     

A rapid method for interfacial tension calculation between rock plug and crude oil based on contact angles,application for EOR

Interfacial tension and contact angle are two specific important parameters to take decisions for enhanced oil recovery, for instance, proper chemicals to use for surface tension reduction, expected wettability of solids, interaction between crude oil and rock. For this purpose, the article presents a method for easy calculation of the solid-liquid interfacial tension based on contact angle measurements applying Neumann's correlation and Young's equation. The main idea stands on the calculation of the rock parameters, like wettability, with known substances and extend these results to crude oils. It was possible, based on the results obtained, to establish a relationship between solid-liquid interfacial tension and contact angle for the crude oil – rock system, which can definitively be used for the calculation of interfacial tension of any other fluid spread out on the same kind of rock. A linear regression was obtained with an accuracy as good as R² = 0.9989. Viscosity as a function of contact angle could also be obtained for the studied crude oils in the same kind of rock.     

非烃化合物引起的润湿性的变化

润湿性是控制油藏中流体的位置、流动和分布的主要因素 ,原油中的非烃化合物对油藏润湿性起着重要作用 ,但其中影响润湿性的主要因素至今尚未确定。作者对塔里木盆地的海相和陆相两类原油进行组分分离 ,利用人造岩心 ,按照Amott方法测定和分析了非烃化合物与沥青质的浓度对润湿指数的影响 ,并研究了原油中各组分的含量与润湿性的关系。实验表明 :①同种原油中非烃和沥青质对润湿性的影响情况相似 ,但不同原油中的非烃或沥青质对润湿性的影响有很大差异。据红外光谱分析 ,含强极性基团的非烃化合物比含弱极性基团的非烃化合物对润湿性的影响大。②油湿指数与原油中的烃类、非烃中的胺和吡咯氮等馏分的含量之间无确定关系 ,但与非烃中的吡啶氮馏分的含量呈正相关关系     

硫酸盐浓度对水驱提高采收率的影响

水驱提高采收率对注入水的离子组成有一定的要求,为了验证润湿性改变不是硫酸盐水驱提高原油采收率的唯一因素,在岩心润湿性为水湿的条件下进行水驱,研究了硫酸盐浓度、温度、注入速率和原油类型对硫酸盐水驱采收率的影响。结果表明,在水驱过程中,原油采收率随着硫酸盐浓度的增加而增加。在40℃下水驱提高采收率无明显增幅,随着温度的升高水驱效果增强。在高温条件下,高浓度硫酸盐水驱的原油采收率比不含硫酸盐水驱的提高10%。原油类型及驱替速率对水驱效果的影响较大,原油中的沥青质含量越高、驱替速率越大,水驱效果越好。在岩心润湿性没有改变的条件下,SO₄^2-仍有助于原油采收率的提高,岩心润湿性改变不是硫酸盐水驱提高原油采收率的唯一因素。     

Variations in wetting behavior of mixed-wet cores resulting from probe oil solvency and exposure to synthetic oil-based mud emulsifiers

Mixed wettability (MXW) results from adsorption from crude oil on rock surface which is not overlain by bulk water. Crude oil/brine/rock interactions and their effect on oil recovery are often investigated after replacing the crude oil with a mineral oil. If crude oil is displaced directly by mineral oil, extreme wettability alteration, referred to as MXW-DF (direct flood), is observed. Less change is observed if an intermediate solvent, such as decalin, is used to avoid destabilization of asphaltenes contained in the crude oil; wettability conditions attained by this treatment are referred to as MXW-F (film). The oil used in a displacement test is referred to as the probe oil, the most common choice being either crude oil or mineral oil. There is strong practical interest in developing MXW-F cores that have wetting properties that are comparable to wettability at reservoir conditions. The main objective of this work is to compare the effect of probe oil solvency, characterized by refractive index, on wetting behavior, characterized by spontaneous imbibition, with MXW wettability given by the parent crude oil. The tested probe oils included mineral oils, alkanes, decalin, toluene, alpha-methylnaphthalene (AMN), crude oils and modified crude oils with both increased and reduced solvency, and base oils and solutions of emulsifiers used in synthetic oil-based mud (SBM) formulations. Wettability established by direct displacement of crude oil with an alkane (MXW-DF) showed systematic increase in water wetness with increase in solvency of the probe oil. Other approaches to tuning MXW-F wettability states by choice of probe oil are also presented. Base oils used in the formulation of SBM had essentially no effect on the imbibition behavior of MXW-F, whereas exposure of MXW-F cores to two kinds of emulsifier resulted in persistently suppressed imbibition for a wide range of probe oils.     

Novel application of PEG/SDS interaction as a wettability modifier of hydrophobic carbonate surfaces

Wettability alteration of carbonate reservoirs from oil-wet to water-wet is an important method to increase the efficiency of oil recovery. Interaction between surfactants and polymers can enhance the effectiveness of surfactants in EOR applications. In this study, the interaction of polyethylene glycol (PEG) with an ionic surfactant, sodium dodecyl sulphate (SDS), is evaluated on an oil-wet carbonate rock surface by using contact angle measurements. The results reveal that wettability alteration of carbonate rocks is achieved through PEG/SDS interaction on the rock surface above a critical aggregation concentration (CAC). The behaviour of PEG/SDS aqueous solutions is evaluated using surface and interfacial tension measurements. Furthermore, the effect of PEG and SDS concentrations and impact of electrolyte addition on PEG/SDS interaction are investigated. It is shown that electrolyte (NaCl) can effectively decrease the CAC values and accordingly initiate the wettability alteration of rocks. Moreover, in a constant SDS concentration, the addition of NaCl leads to a reduction in the contact angle, which can also be obtained by increasing the aging time, temperature and pre-adsorption of PEG on the rock surface.     

An evaluation of modified silica nanoparticles’ efficiency in enhancing oil recovery of light and intermediate oil reservoirs

The role of nanoparticles in enhancing oil recovery from oil reservoirs is an increasingly important topic of research. Nanoparticles have the properties that are potentially useful for enhanced oil recovery processes, as they are solid and two orders of magnitude smaller than colloidal particles. This paper presents a comparison between the efficiency of modified silica nanoparticles in enhancing oil recovery from two different Iranian light and intermediate oil reservoirs. The mechanisms used to recover additional oil would be oil–water interfacial tension reduction and wettability alteration. Oil phase contact angles and oil–water interfacial tensions were measured in the absence and the presence of nano fluids’ different concentrations (1–4 g/L). Results showed that the interfacial tension reduces dramatically in the presence of nanoparticles for both light and intermediate oil. In addition oil phase contact angle results showed a transformation of rock wettability from water-wet toward oil-wet condition. However, these nanoparticles are more capable in the reduction of the interfacial tension and the alteration of wettability in the case of light oil reservoir. A comparison between recovery results indicated that these nanoparticles are more efficient in light oil reservoirs and produce more incremental amount of oil after primary and secondary processes.     

表面活性剂与页岩油岩石和流体作用机理的试验研究

页岩油藏由于特殊的成藏模式和储层特征,储层非常致密,纳米级孔隙、喉道发育,原油流动阻力大,页岩油整体的采收率较低。通过开展接触角、界面张力和洗油试验等研究,明确不同类型的表面活性剂与页岩油岩石和原油之间相互作用的机理,判断是否可以采用表面活性剂来提高页岩油采收率。试验结果表明,表面活性剂可以改变页岩油岩石表面润湿性、降低界面张力,并能起到乳化的作用,最终实现提高洗油效率的效果。     

FLUID-FLUID AND SOLID-FLUID INTERFACIAL INTERACTIONS IN PETROLEUM RESERVOIRS

The distribution and flow behavior of crude oil, gas and brine in the porous rock medium of petroleum reservoirs are controlled largely by the interactions occurring at the interfaces within the various fluids and by the interactions between the fluids and the rock surface. With an objective to correlate the macroscopic multiphase flow behavior with fundamental interfacial interactions, the recent developments in the field of fluid-fluid and solid-fluid interactions and their applications in petroleum engineering are presented in this contribution.

A computerized drop shape analysis technique and its application to the measurement of fluid-fluid interfacial tension at elevated pressures and temperatures are discussed. A recently developed technique that is capable of measuring dynamic (advancing and receding) contact angles at realistic conditions encountered in petroleum reservoirs is presented. Its effectiveness in making reproducible and rapid measurements relative to the conventional techniques is demonstrated with several reservoir case studies.

Attempts are made to correlate the interfacial phenomena of adhesion and spreading in solid-liquid-liquid systems with dynamic contact angles as well as to extend the applicability of the critical surface tension concept from the conventional solid-liquid-vapor systems to the rock-oil-brine systems of interest in petroleum engineering. These interfacial concepts have been applied to the practical problems of asphaltene destabilization from crude oils and the effect of temperature on wettability alteration in heavy oil fields. A simple procedure is outlined to enable the estimation of interfacial adhesion forces and to demonstrate the significant role they play relative to the capillary forces in retaining the fluids within the porous rock medium.     

FLUID–FLUID AND SOLID–FLUID INTERFACIAL INTERACTIONS IN PETROLEUM RESERVOIRS

The distribution and flow behavior of crude oil, gas and brine in the porous rock medium of petroleum reservoirs are controlled largely by the interactions occurring at the interfaces within the various fluids and by the interactions between the fluids and the rock surface. With an objective to correlate the macroscopic multiphase flow behavior with fundamental interfacial interactions, the recent developments in the field of fluid–fluid and solid–fluid interactions and their applications in petroleum engineering are presented in this contribution.

A computerized drop shape analysis technique and its application to the measurement of fluid–fluid interfacial tension at elevated pressures and temperatures are discussed. A recently developed technique that is capable of measuring dynamic (advancing and receding) contact angles at realistic conditions encountered in petroleum reservoirs is presented. Its effectiveness in making reproducible and rapid measurements relative to the conventional techniques is demonstrated with several reservoir case studies.

Attempts are made to correlate the interfacial phenomena of adhesion and spreading in solid–liquid–liquid systems with dynamic contact angles as well as to extend the applicability of the critical surface tension concept from the conventional solid-liquid-vapor systems to the rock-oil-brine systems of interest in petroleum engineering. These interfacial concepts have been applied to the practical problems of asphaltene destabilization from crude oils and the effect of temperature on wettability alteration in heavy oil fields. A simple procedure is outlined to enable the estimation of interfacial adhesion forces and to demonstrate the significant role they play relative to the capillary forces in retaining the fluids within the porous rock medium.     

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。     

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.     

生物酶改变岩石表面润湿性实验研究

根据岩石润湿性的衡量标准,用光学投影法测定岩石接触角,对生物酶改变岩石表面润湿性进行了实验研究,包括生物酶与岩石作用后岩石润湿性的变化、毛管力的变化以及粘附功的变化。实验结果表明,生物酶与岩石作用后,可以明显改变水驱油毛营力的大小,可以加速剩余油的流动,从而提高油藏的采收率。     

Beneficial effects of wettability altering surfactants in oil-wet fractured reservoirs

In fractured reservoirs, an effective matrix-fracture mass transfer is required for oil recovery. Surfactants have long been considered for oil recovery enhancement, mainly in terms of their ability to reduce oil–water interfacial tension. These surfactants are effective when the fractured formations are water-wet, where capillary imbibition of surfactants from the fracture into the matrix contributes to oil recovery. However, another beneficial aspect of surfactants, namely their ability to alter wettability, remains to be explored and exploited. Surfactants capable of altering wettability can be especially beneficial in oil-wet fractured formations, where the surfactant in the fracture diffuses into the matrix and alters the wettability, enabling imbibition of even more surfactant into the matrix. This sequential process of initial diffusion followed by imbibition continues well into the matrix yielding significant enhancements in oil recovery.In order to test this hypothesis of sequential diffusion–imbibition phenomenon, Dual-Drop Dual-Crystal (DDDC) contact angle experiments have been conducted using fractured Yates dolomite reservoir fluids, two types of surfactants (nonionic and anionic) and dolomite rock substrates. A new experimental procedure was developed in which crude oil equilibrated with reservoir brine has been exposed to surfactant to simulate the matrix-fracture interactions in fractured reservoirs. This procedure enables the measurements of dynamic contact angles and oil–water interfacial tensions, in addition to providing the visual observations of the dynamic behavior of crude oil trapped in the rock matrix as it encounters the diffusing surfactant from the fractures. Both the measurements and visual observations indicate wettability alterations of the matrix surface from oil-wet to less oil-wet or intermediate wet by the surfactants. Thus this study is of practical importance to oil-wet fractured formations where surfactant-induced wettability alterations can result in significant oil recovery enhancements. In addition, this study has also identified the need to include contact angle term in the dimensionless Bond number formulations for better quantitative interpretation of rock–fluids interactions.     

How much would silica nanoparticles enhance the performance of low-salinity water flooding?

Nanofluids and low-salinity water(LSW)flooding are two novel techniques for enhanced oil recovery.Despite some efforts on investigating benefits of each method,the pros and cons of their combined application need to be evaluated.This work sheds light on performance of LSW augmented with nanoparticles through examining wettability alteration and the amount of incremental oil recovery during the displacement process.To this end,nanofluids were prepared by dispersing silica nanoparticles(0.1 wt%,0.25 wt%,0.5 wt% and 0.75 wt%)in 2,10,20 and 100 times diluted samples of Persian Gulf seawater.Contact angle measurements revealed a crucial role of temperature,where no wettability alteration occurred up to 80 ℃.Also,an optimum wettability state(with contact angle 22°)was detected with a 20 times diluted sample of seawater augmented with 0.25 wt% silica nanoparticles.Also,extreme dilution(herein 100 times)will be of no significance.Throughout micromodel flooding,it was found that in an oil-wet condition,a combination of silica nanoparticles dispersed in 20 times diluted brine had the highest displacement efficiency compared to silica nanofluids prepared with deionized water.Finally,by comparing oil recoveries in both water-and oil-wet micromodels,it was concluded that nanoparticles could enhance applicability of LSW via strengthening wettability alteration toward a favorable state and improving the sweep efficiency.     

严重生物降解稠油沥青质包裹体中生标的研究

对孤岛原油中的可溶有机质生物标志化合物进行了气相色谱—质谱分析,结果表明,该原油受到了严重的生物降解,部分用于对比的生物标志物受到了破坏,致使有关参数值发生了变化,给油—油对比、油—源对比带来了困难。采用超声萃取技术,分离出沥青质包裹体中抗生物降解的生物标志物,并与原油中的生物标志物进行对比。其结果显示沥青质包裹体组分与原油组分的甾、萜烷非常相似,C₂₇,C₂₈,C₂₉规则甾烷类分布均呈"L"型,而与生物降解程度无关,表明此方法可完全用于强烈生物降解原油的油—油对比和油—源对比研究,在有机地球化学领域的研究中具有重要的指导意义。      

Comparison of in-situ and ex-situ microbial enhanced oil recovery by strain Pseudomonas aeruginosa WJ-1 in laboratory sand-pack columns

Microbial enhanced oil recovery (MEOR) applies biotechnology to improve residual crude oil production from substratum reservoir. MEOR includes in-situ MEOR and ex-situ MEOR. The former utilizes microbial growth and metabolism in the reservoir, and the latter directly injects desired active products produced by microbes on the surface. Taking biosurfactant-producing strain Pseudomonas aeruginosa WJ-1 for research objects, in-situ enhanced oil recovery and ex-situ enhanced oil recovery by biosurfactant-producing strain WJ-1 were comparatively investigated in sand-pack columns.The results showed that P.aeruginosa WJ-1 really proliferated in sand-pack columns, produced 2.66 g/L of biosurfactant, altered wettability, reduced oil-water interfacial tension (IFT) and emulsified crude oil under simulated in-situ process. Results also showed that higher biosurfactant concentration, lower IFT, smaller average diameters of emulsified crude oil were obtained in in-situ enhanced oil recovery experiment than those in ex-situ enhance oil recovery experiment. Similar wettability alteration was observed in both in-situ and ex-situ enhanced oil recovery experiment. The flooding experiments in sand-pack columns revealed that the recovery of in-situ was 7.46%/7.32% OOIP (original oil in place), and the recovery of the ex-situ was 4.64%/4.49% OOIP. Therefore, in-situ approach showed greater potential in enhancing oil recovery in contrast with ex-situ approach. It is recommended that the stimulation of indigenous microorganisms rather than injection of microbial produced active products should be applied when MEOR technologies were employed.