Emulsions In Porous Media Research Articles

Experimental and numerical study of the water-in-oil emulsions in porous media

Experimental and numerical study of the water-in-oil emulsions in porous media

Study of the liquid resistance effect of water-in-oil emulsions in porous media

During heavy oil recovery in the Bohai Oilfield, substantial emulsification of oil and water occurred, primarily forming water-in-oil (W/O) emulsions. This phenomenon could alter fluid dynamics within the subsurface porous media, potentially impacting well production performance. To elucidate the properties of water-in-oil emulsions and their associated liquid resistance effects, this study conducted a series of rheological tests, microscopic examinations, and injection experiments. The results show that the droplet size and distribution of water-in-oil emulsions were primarily influenced by shear rate and water content, which in turn modified emulsion viscosity. The stability of water-in-oil emulsions was reduced when they flowed through porous media. The increase in emulsion viscosity and the liquid resistance effect collectively enhanced the seepage resistance of water-in-oil emulsions flowing through porous media. Notably, when the emulsion droplet size exceeded the pore throat size, over 90% of the total seepage resistance was attributable to the liquid resistance effect. Conversely, when the majority of the emulsion droplets were smaller than the pore throat, the viscosity accounted for more than 60% of the seepage resistance. Water-in-oil emulsions flowed through cores with permeabilities ranging from 50 to 100 mD, exhibiting threshold pressure gradients between 35 and 43 MPa/m. At a core permeability of 300 mD, the threshold pressure gradient was significantly reduced to 1 MPa/m. The presence of a water-in-oil emulsion in the reservoir could result in a production pressure differential falling below the threshold pressure, thereby reducing reservoir productivity.

Investigation of microflow mechanisms and emulsion size distribution in porous media

Crude oil in underground porous media can be emulsified by surfactants, which can lead to improved oil recovery. However, there have been limited investigations revealing the interactions between emulsions and grains and comparing the influence of different factors on the distribution of emulsions in porous media at the pore scale. In this study, a solution containing surfactant was injected into an oil-saturated microchip with heterogeneous pore geometries. A series of tests were conducted by varying the injection rate, surfactant concentration, oil viscosity, and displacing phase viscosity. Qualitative analysis of flow mechanisms and quantitative analysis of the distribution of emulsions were performed through pore-scale snapshots. The results demonstrate that emulsions undergo deformation, breakup, and retention in porous media. Furthermore, new micro-interactions between emulsion droplets and grains are discovered, including the impact effect, cutting effect, and the synergy of both effects. A high flow rate of the displacing phase promotes the formation of more and smaller emulsions, while a low flow rate encourages flow diversion. An increase in oil viscosity and a decrease in surfactant concentration are not conducive to the formation of emulsions. However, an increase in the displacing phase viscosity promotes the formation of emulsions and flow diversion. The experiments provide detailed insights into the flow behaviors of emulsions at pore scale and offer valuable information for surfactant flooding.

Studying the Transmission Behavior of Two-Phase Flow Oil-Water Mixing Using a Laboratory Multiple Porous Media Model

The formation and flow of emulsions in porous media are common to all technologies used to extract or process oil. In most cases, oil and water emulsions are formed in a porous medium due to oil spills near watery areas or soils containing water. This emulsion leads to a reaction between oil and water, which finds its way to the porous medium. The detailed flow mechanisms of emulsions through porous media are not well understood. In this study, the soil’s oil percentage variation was studied when sand was introduced or an emulsion, i.e., mixed with water, and two porous media, different in composition and physical properties, were used to find out their effect on oil transmission. The percentage of oil and water was calculated at several points at different distances and times. It was noted that the results differed in both mediums due to the difference in permeability, porosity, arrangement of soil particles, compaction process, and other physical properties. Liquids’ viscosity, density, and chemical composition clearly and significantly affect the results. The time for the oil to reach the last point in the pipe differed for both soils. If the time period in the experiment of pumping oil only in sandy soil took 6 hours and the washing process took 3 hours. In organic soil, the time period for the pollutant pumping stage took about 7 hours and the washing stage about 4 hours because the oil is transmitted in sandy soil is faster, but in the experiment of pumping oil and water together, the time period in the process of pumping oil and water together in sandy soil took 4 hours and the washing process 3 hours In organic soil, the period of pumping oil and water together took 5 hours, and the washing period 3 hours, because the percentage of oil was less than in the experiment of pumping oil only. In the soil, that is, if the period of pumping the pollutant increased for more than 15 hours, the oil may reach a distance of more than 4 meters in the soil. As for the washing process, when the oil is mixed with water, it gives better results when washing it than if the oil enters alone into the soil because the proportions of oil when it enters the soil together with the water, it is little and does not rise much, so it is easy to wash.

Non-linear seepage law and a characterization model of heavy oil-in-water emulsion in porous media

Stable emulsions with different continuous-phase viscosities, dispersed-phase volume fractions, and dispersed droplet sizes were prepared. Seepage experiments using heavy oil-in-water (O/W) emulsion were then conducted in sand packs to analyze the effects of different injection rates, permeabilities, and emulsion characteristics on the seepage law. Finally, an evaluation method for the seepage law was established, and a regression model that considered the factors influencing the non-linear seepage laws was developed using the 1stop software to quantitatively reveal the seepage mechanism. The matching relationship between droplet size and permeability determined the seepage behavior of the O/W emulsion. Emulsions with droplet sizes matched with permeability behaved as a pseudoplastic fluid, with a non-linear flow. With an increase in the dispersed-phase volume fraction, the emulsions displayed a more non-linear behavior due to the accumulated retention and disordered plugging of dispersed droplets. With an increase in the injection rate, the emulsion with a low continuous-phase viscosity had more significant non-linear characteristics than the emulsion with a high continuous-phase viscosity. The correlation of the characterization model was relatively strong under the experimental conditions, with a correlation coefficient of 93.28%. Therefore, the characterization model accurately predicted the effects of the non-linear seepage law for all factors studied.

A Three-Phase Relative Permeability Model for Heavy Oil Emulsion System

Chemical flooding is important and effective enhanced oil recovery processes are applied to improve the recovery of heavy oil reservoirs. Emulsification occurs during chemical flooding processes, forming an oil-in-water (O/W) emulsion system. In this work, the heavy oil emulsion system is characterized as a three-phase (continuous oil phase, dispersed oil phase, and continuous water phase) system. Based on a capillary tube model, a new relative permeability model is proposed to describe the flow of the emulsion system in porous media quantitatively, considering the physicochemical properties of emulsions and the properties of porous media. A resistance factor is derived in this model to describe the additional resistance to the emulsion flow caused by the interaction between dispersed oil droplets and the pore system. Three dimensionless numbers related to the emulsion porous flow process were proposed and their different effects on the three-phase relative permeability are investigated. To validate the reliability of the proposed model, a one-dimensional O/W emulsion–oil displacement experiment is simulated. The maximum absolute error between the simulated results and experimental data is no more than 10%, and the new model can be used to describe the flow behavior of heavy oil emulsions in porous media.

Assessing the apparent viscosity of decane-water emulsion in underground porous media based on the lattice Boltzmann method

The groundwater system is one of the most important subsurface resources on Earth, which offers many important services to humankind, such as irrigated agriculture, household use, and manufacturing. However, the safety of groundwater resources is seriously threatened by contamination from human activities. The emulsion has been proposed as a potential solution for the removal of contaminants due to its high apparent viscosity. Here we reveal the pore-scale mechanism for the viscosity increase in decane-water emulsions by lattice Boltzmann simulations. We assess the effect of phase saturation, interfacial tension, and contact angle, on the apparent viscosity of decane-water emulsions in porous media. Our results show that the apparent viscosity of the emulsion reaches its maximum value when the decane saturation is around 20%. We also find that this maximum viscosity increases with interfacial tension, and it is larger in decane-wet or water-wet systems than it is in intermedia-wet media.

Probing the generation mechanism of emulsion based on shearing actions between multiphase fluids in porous media

The generation, migration, and coalescence processes of emulsions in porous media of the actual formations are relatively complex. However, few studies have been reported about the generation mechanism of emulsions under shearing action, especially under shearing action between multiphase fluids. In this paper, the concept of emulsification caused by fluid shearing was proposed for the first time. An oil-water two phases flow model in porous media was established to study the generation process of emulsion caused by shearing actions between oil and water. Fluid flow velocity, pressure and distribution characteristics of oil and water during this process were recorded. The effects of flow velocity and oil-water interface properties on the generation process of emulsion were investigated. Combined with the microscopic visualization oil displacement model, the generation characteristics of emulsions in porous media were further explored. The results indicated that the complex flow between oil and water in porous media would cause shear emulsification of crude oil. With the increase of flow velocity of oil-water two phases, the shear emulsification capacity was gradually enhanced. The generation capacity of emulsion in the micro shearing unit was mainly affected by the flow velocity of the displacing phase, and the particle size of the emulsion was mainly affected by the flow velocity of the shearing phase. When the interfacial tension between oil and water was lower than 10−1 mN/m, the shear emulsification rate did not change significantly. These results are of great significance for the supplement and improvement of the generation mechanism of emulsions in porous media, providing theoretical guidance for further enhancing oil recovery by regulating emulsification.

Study on the chemical structure characterization and emulsification-stripping of heavy oil

The viscosity of heavy oil is of great importance on crude oil recovery, and the intrinsic relationship between the molecular structure of heavy oil and its viscosity is still unclear. To this end, the chemical structure of heavy oil is characterized by Scanning Electron Microscopy (SEM) and Diffusion-ordered Spectroscopy (DOSY). The relationship between the molecular structure and viscosity of heavy oil is revealed. The morphology of molecular aggregates is dominated by spherical particles, vesicles and films, and the corresponding viscosity increases sequentially. DOSY show that the heavy oil molecules rapidly gathered into aggregates with increasing concentrations. If the saturated aggregation concentration (maximum degree of aggregation) is exceeded, the volume of the single aggregate remains generally fixed but its quantity begins to increase. In addition, the structure-activity relationship between chemical agents and emulsification-stripping, including their mechanism of effect are systematically studied by interfacial tension (IFT), emulsification and micromodel experiments. The results show that the hydrophilic-lipophilic balance (HLB) values of surfactants that stabilize the emulsions are between 13.7 and 14.5. There is no obvious consistency between the emulsification effect of the surfactant and its IFT, and the stripping effect depends on its permeation and wetting action on the solid interface. The formation of emulsions in porous media mainly depends on the rotational disturbance and shear fracture of the displacing fluid, and the wettability of the solid surface determines the peeling rate of the oil film. Comparing with the blockage of large-sized emulsions, the migration of small-sized droplets in the channels as a continuous phase contributes more to the enhanced oil recovery.

Study on the matching relationship between dispersed droplet size in O/W emulsion and reservoir permeability

Formation and percolation of emulsion are important to enhance heavy oil recovery through emulsification. The percolation behavior of emulsion is affected by permeability, concentration of emulsion, oil-water ratio, etc. To ensure the stable flow of emulsion in porous media and improve the oil-carrying capability of emulsion, it is necessary to study the matching relationship between dispersed droplet size in emulsion and reservoir permeability. The emulsion was prepared by a mulser, and then a series of sand pack flow tests were conducted to investigate the effects of the size of dispersion droplet, permeability and oil-water ratio on percolation. Based on the analysis of displacement pressure, variation of droplet size and oil-carrying capability, the paper established a matching relationship between droplet size and permeability. Due to the shear effect of throat and pore, injection pressure increased, and droplet size became smaller as the injection volume increased in the low permeability sand packs, which shown a poor matching relationship. Then, the permeability increased gradually until the flowing droplet size was remained constant, and the injection pressure was relativity stable. At the point, it can be confirmed that the permeability and the injected droplet size matched well. The study of Influencing factor indicated that the matched droplet size increased with the increase of reservoir permeability. In detail, when the permeability was about 2.76 μm2, the matched droplet median diameters (D50) was about 3.60 µm. When the permeability was about 4.34 μm2, the matched D50 was about 7.04 μm. When the permeability was about 5.60 μm2, the matched D50 was approximately 11.03 μm. In addition, increasing the oil-water ratio of emulsion contributed to shortening the breakthrough time of the emulsion, thus the matched droplet size became a little smaller.

Pore-scale investigation on occurrence characteristics and conformance control mechanisms of emulsion in porous media

Microscopic computed tomography (Micro-CT) is used to visualize microscopic flow in sandstone core samples during emulsion flooding. The images obtained during the experiment are processed quantitatively with a series of methods to evaluate the occurrence characteristics and oil recovery enhancement mechanisms of emulsion. (1) The emulsion is distributed in the cores in spherical shape, and its sphericity is significantly different from that of the remaining oil. Sphericity can be taken as a characteristic parameter to identify emulsion. (2) The emulsion with specific size prefers to stay in pores with matching sizes; when the emulsion volume is smaller than the product of the lower limit of pore occupancy and the corresponding pore volume, it will not be able to effectively trap in the pore to achieve conformance control. In the process of emulsion displacement designing, we need to design emulsion with suitable particle size according to the pore distribution of the reservoir. (3) Mobilization ratio of the pores can be increased from 23.1% to 59.3% by emulsion flooding after subsequent water flooding, and the average oil displacement efficiency at the pore-scale can be increased from 22.9% to 75.8% under the test conditions; (4) After emulsion flooding, the clustered remaining oil and the oil phase in the trapped emulsion are the main targets for further EOR.

Emulsions in porous media from the perspective of produced water re-injection – A review

During offshore production, it is typical to discharge produced water into the sea after treating it to a level that meets environmental regulations. A growth in the volumes of produced water and increasingly stringent requirements have drawn attention to re-injection of produced water as a more viable disposal method. Produced water re-injection is regarded as an environmentally friendly and cost-efficient approach that allows integration of produced water with reservoir management. However, loss of injectivity, due to the plugging of pores by oil droplets and particles present in produced water, limits implementation of re-injection. This review discusses engineering challenges during re-injection and summarizes the knowledge and the gaps in the literature on the permeability reduction due to the flow of dilute oil-in-water emulsions. First, a short introduction into the origins of produced water, its composition, and the treatment techniques employed offshore are provided. An overview of the water injection strategies as well as a discussion of the past field experience of produced water re-injection is given. This is followed by a detailed review of the flow of diluted oil-in-water emulsions through porous media from the permeability reduction perspective. An overview of models for predicting permeability reduction during the flow of emulsions is provided. The physical parameters affecting the droplet retention and physicochemical interactions between droplets and pore walls are discussed. The studies that investigated co-injection of oil droplets and solid particles are included as well. The review identified that the effect of droplet stability, oil viscosity, wettability, and particles on droplet retention is not sufficiently examined. It was found that drop-to-pore size ratio is a crucial factor for droplet retention, but it is often omitted in the industry. An outlook on the gaps and suggestions to address them was provided. Microfluidics was pointed out as a complementary technique to coreflooding.

Seepage Characterization of Oil-in-Water Emulsion in Porous Media in Marine Sandstone Reservoirs

Interfacial tension is a crucial factor affecting emulsion flow behavior in porous media. Finding the emulsion flow properties under different interfacial tensions is important to the potential use of emulsion in field enhanced oil recovery (EOR) applications. In this study, oil-in-water (O/W) emulsions were first prepared with different interfacial tensions. Then, a set of sandpack flow experiments were conducted to study how the interfacial tension affects the plugging ability of oil-in-water (O/W) emulsion when flowing in porous media. After that, a regression model, which considered the interfacial tension factor for the first time, was developed using MINITAB to determine the emulsion plugging ability characterized by effective viscosity. The results show that the interfacial tension between oil and water in the O/W emulsion system had a significant effect on the emulsion plugging ability. The plugging pressure of emulsion in sandpacks increases with the increase in interfacial tension. This is probably because the strength of the film between oil droplets and water became higher as the interfacial tension increased. The newly developed regression model, which incorporates the interfacial tension effect to describe the emulsion effective viscosity in different sandpacks, has a good correlation with experimental data. From error analysis, the correlation coefficient R²ₐdⱼ and mean absolute relative error MAER between the calculated and experimental results are 0.994 and 4.64%, respectively. The regression model could be used for prediction for the O/W emulsion effective viscosity in porous media with relatively high accuracy.

Modeling and experimental data of the flow of highly concentrated emulsions in porous media

This paper gives a theoretical model which allows to predict changes of the blockade of the porous bed during the flow of non-Newtonian emulsions. It takes into account much more process and material parameters than the formulas published in the literature till now: like size of dispersed phase droplets, emulsion concentration and rheological parameters of heterogeneous, non-Newtonian liquid. Using the model it is also possible to predict changes of bed permeability, its blockade, as a result of oil droplets capture. Model calculations were verified with experimental data and satisfactory correctness was obtained. The work contributes to the development of the description of the transport of multiphase substances, with complex rheological properties, through porous structures. The results of the research may find practical application during the development of methods of intensifying oil production, as well as the assessment of the penetration of complex pharmaceuticals in dermal structures.

Visualizing in-situ emulsification in porous media during surfactant flooding: A microfluidic study

HypothesisIt is well recognized that crude oil could be emulsified during surfactant flooding process, and recently such an in-situ emulsification was found practically helpful for enhanced oil recovery (EOR). However, no direct proofs are reported yet to unravel how emulsion is formed in porous media and how important to increasing oil recovery factor due to unavailability to visualize the emulsification process, thus it is desirable to verify visibly the formation of emulsion in porous media and the contribution of emulsification to EOR process. ExperimentsTwo types of microfluidic chips with heterogeneous and homogeneous pore geometries respectively were employed to simulate the underground oil reservoir environment. Sodium dodecylbenzenesulfonate (SDBS) was selected as a model surfactant, and its aqueous solution was injected into the paraffin oil-saturated microchip to mimic the displacing process. A series of tests were conducted by varying SDBS concentration, electrolyte content, injection rate, and pore-scale snapshots were captured for qualitative and quantitative analysis of in-situ emulsification during the surfactant flooding. FindingsBoth oil-in-water (O/W) and water-in-oil (W/O) emulsions are formed in microchips during the surfactant flooding. Increasing SDBS concentration, migration distance, injection rate, or addition of electrolyte tends to form smaller O/W particles through snapping action at pore throat, and vice versa. Smaller size endows oil with a better mobility to go through the pore throat, and up to 24% extra emulsion can be achieved through emulsification entrainment; bigger droplets can block the dominant paths, thus improving sweep efficiency and increasing oil recovery factor up to 30% compared to waterflooding. Furthermore, W/O emulsification was found to be a time-dependent process influenced by SDBS concentration, and oil was recovered by diffusing surfactant solution into oil phase and replacing the oil-occupied space in porous media.

A model of emulsion plugging ability in sandpacks: Yield pressure drop and consistency parameter

In this study, a total of 20 sandpack flood tests, each with 11 different flow rates, were conducted to evaluate oil-in-water (O/W) emulsion plugging ability in sandpacks. Four conditions of emulsion flow in porous media were observed, identified, and discussed, in terms of the capillary number. A general model for the pressure drop versus flow rate based on the bi-viscosity model was developed from a comprehensive analysis of the experimental data. This model expresses that the flow of emulsion in porous media has two distinct mobility in porous media demarcated by a critical pressure drop. The inverse of the mobility is determined as consistency parameter and the critical pressure drop as the yield pressure drop. Effects of interfacial tension (IFT), emulsion quality, droplet size, emulsion slug size, and sandpack permeability on the yield pressure drop and consistency parameter were experimentally and numerically investigated. The newly proposed model has a good agreement between the predicted and experimental plugging pressure drop of emulsion. Besides giving guides on preparation of O/W emulsions and injection strategies in a specific oil reservoir, use of the proposed model can also help model reservoir scale O/W emulsion flow to reduce or shut-in the mobility in thief zones.

Performance and displacement mechanism of a surfactant/compound alkaline flooding system for enhanced oil recovery

Monoethanolamine and sodium carbonate were simultaneously applied with sulfonate surfactant to form a surfactant/compound alkaline flooding system, whose optimized composition is 0.20% SLPS, 0.15% Na2CO3, and 0.10% MEA. This system has better anti-salt performance. It can significantly decrease the oil/water interfacial tension (IFT) to ultra-low (＜10−3 mN/m) when NaCl concentration is lower than 40,000 mg/L, CaCl2 concentration is less than 400 mg/L, and the temperature is below 90℃. Because of the synergistic effect among SLPS, MEA and Na2CO3, the flooding system shows obviously higher emulsion stability. Micro displacement experiments were performed to investigate the displacement mechanisms of the system. Results indicate that the oil/water IFT reduction and interfacial film softening are two fundamental micro mechanisms which can make crude oil easy to be emulsified by the flooding system. According to the flow velocity and the contact time between crude oil and the system, turbulent-emulsification and self-emulsification are main emulsification mechanisms. During the migration process of emulsion in porous media, the coalescence-entrainment and the coalescence-dispersion phenomena appear, which both can improve the displacement efficiency of remaining and irreducible oil and ultimately enhance the crude oil recovery.

The influence of surfactants on the flow characterization of heavy oil

Flow characteristic of oil-in-water emulsion for heavy oil in porous media was studied. A surfactant was screened out and subsequently utilized as the emulsifier in sandpack flooding experiments with different oil-water ratio and permeability. The dual sandpack flooding experiment was conducted to investigate the effect of emulsion in porous media and the ability to enhance oil recovery. Results indicated that the selected surfactant gave a remarkable flow resistance in porous media. Higher oil-water ratio and lower permeability resulted in higher flow resistance. The surfactant increased ultimate recovery of 7.7% by diverting the fluid into low permeability sandpack.

Oil emulsions in naturally fractured Porous Media

Abstract Most of the studies regarding the formation and stability of emulsions focus on the conditioning and management of crude oil on surface facilities. Since a great deal of the crude oil produced is in the form of stable emulsions, it is often claimed that these emulsions are formed through chokes and other flow constrictions in oil field equipment. However, emulsions are produced in wells, which not only lack these constrictions but also are produced at low flow rates, demonstrating the fact that emulsions can be formed within the well itself. The present work reviews the literature regarding the formation and properties of heavy and extra-heavy oil emulsions in naturally fractured porous media due to the current relevance that these types of crude oil exploitation take, satisfying the hydrocarbon energy demand. Moreover, emulsions have received more attention recently since they can be formed in-situ and improve oil recovery. To understand the flow mechanics of emulsions in porous media, different models to describe their transportation are presented. Finally, the formation of emulsions in the reservoir for enhanced oil recovery purposes, including the use of nanoparticle-stabilized emulsions is discussed.

A Comprehensive Review on Emulsions and Emulsion Stability in Chemical and Energy Industries

AbstractEmulsion refers to a mixture that includes two or more liquid phases. The uses of emulsions are found in several chemical, energy, and environmental industries such as the food, health care, chemical synthesis, and firefighting sectors. Water‐in‐oil emulsions are formed spontaneously during oil production when oil and water are mixed together and in the presence of asphaltene as a naturally occurring surfactant. For operational and economic reasons, oil emulsions need to be treated to recover both oil and water phases. To develop more efficient emulsion treatments, it is essential to have a better understanding of the factors that affect emulsion formation and stability. The droplet size variation is an important parameter that influences the stability and rheological characteristics of the emulsions. In addition, the available interfacial area for any possible chemical reactions might affect the behaviours and properties of the emulsions in various transport phenomena systems. The adequate knowledge of the factors and mechanisms affecting the droplet size and emulsion stability still needs further engineering and research activities. This study is aimed to provide a comprehensive literature review on the formation of water/oil emulsions and their stability in various physical systems (e.g., pipeline networks and porous media). In this review, fundamental aspects of emulsions, emulsion formation mechanisms, analytical models, and numerical solutions for the description and characterization of the behaviours of emulsions in porous media and/or separators are discussed. The effects of different fluid properties, physical model characteristics, and operational conditions on emulsion behaviours are studied. This paper also summarizes the previous experimental and modelling studies and methodologies with a focus on reliable laboratory equipment/tools and simulation and modelling packages/strategies for the investigation of emulsion stability and droplet size distribution where a systematic parametric sensitivity analysis to study various effects of important thermodynamic, process, and medium properties on the targeted variables is conducted. This review manuscript provides useful guidelines to characterize and model emulsions and their behaviours in different industrial sectors, which will considerably help to conduct better design and optimal operation of corresponding equipment.