Foam In Porous Media Research Articles

Investigation of synergism between surface-grafted nano-cellulose and surfactants in stabilized foam injection process

Abstract The enhanced oil recovery (EOR) efficiency of a foam injection is largely dependent on the stability of foam film especially when crude oil is present. In this study, a surface-grafted nano-cellulose (sgNC) was used to stabilize the film of a surfactant foam and then employed in foam EOR process. The synergism between sgNC and the surfactant was first investigated in bulk through direct measurements of oil/water/solid interfacial behaviors, foam morphology, foam decay, interfacial dilational rheology, etc. Particular emphasis was placed on the microflow behaviors of the sgNC stabilized foam in porous media with crude oil to understand the EOR mechanisms behind. The results showed that the incorporation of sgNC in the surfactant solution further reduced the oil/water IFTs, and enhanced the emulsifiability and wettability alteration of the surfactant because of its amphiphilicity. The presence of sgNC in the surfactant foam film significantly increased the film thickness and obstructed liquid drainage. The resultant foam film was fairly viscoelastic, as revealed by the rheological analysis. The oil displacement dynamics observed in the visual microflow model indicated that the viscoelasticity of the foam film rendered the gas bubbles superior stability during migrating in porous media, thus leading to a favorable mobility control and significant reduction in the residual oil saturation. Emulsification, Jamin effect and squeezing accounted for the EOR of foam injection at pore scale.

Fractal characterization of dynamic structure of foam transport in porous media

The evaluation and simulation of foam fluid are still matters of significant debate despite the large number of available studies due to the excellent properties of foam and its successful applications, especially in oil and gas field development. The properties of foam fluid are substantially determined by its dynamic structure in porous media; however only a few studies that investigate and perform measurements related to such structure have been reported. In this research, a new method based on fractal theory is proposed for evaluation of aqueous foam in porous media. As a first step, the fractal characteristics of foam in porous media are confirmed by image processing and calculations. Accordingly, the foam dynamic structure is quantitatively studied by defining and calculating the foam fractal dimension. Secondly, a concise relation is established which reveals that the foam fractal dimension is nearly time-independent. Finally, a sensitivity analysis is carried out by discussing three major factors affecting foam structure in porous media. These results are expected to be helpful for further understanding the dynamic characteristics of foam fluids and their advanced applications.

Relationship between bulk foam stability, surfactant formulation and oil displacement efficiency in porous media

Success of foam as a displacing fluid in porous media depends on longevity of foams in the presence of non-aqueous phase liquids such as hydrocarbons. The stability of foam at bulk scale has been used in many cases to screen potential surfactants for core flooding studies. Although this method may aid in determining the foamability and stability of a surfactant, no reliable correlation has been found to exist between bulk foam stability and performance in porous media. We have conducted a comprehensive series of experiments to examine and compare the stability of selected surfactant foams at bulk scale and during oil displacement in porous media. The oil displacement was investigated in a micromodel manufactured by 3D printing technology. Our results demonstrated that oil displacement efficiency by foam is strongly influenced by the surfactant formulation. More importantly, no meaningful correlation between the bulk foam stability and the oil displacement efficiency of the corresponding foams in porous media was observed. Our pore-scale investigation shows that the stability or instability of foam at bulk scale does not necessarily determine its effectiveness in porous media. Hence, performing displacement tests as presented in our study may give more insights into the potential performance of foams.

Experimental study on the dynamic filtration control performance of N2/liquid CO2 foam in porous media

Liquid CO2 has been successfully used as a fracturing fluid and injected into rock formations to enhance oil and gas production. However, the difficulty in controlling the filtration of liquid CO2 in porous media limits its application. The goal of this study is to investigate the dynamic filtration control performance of N2/liquid CO2 foam with a fluorochemical (HFE) as stabilizer. A laboratory apparatus has been specially designed and built for the generation of N2/liquid CO2 foams and the measurement of their viscosity and filtration rate under high pressure (10–25MPa). The test results show that after liquid CO2 and HFE were mixed with N2, the N2/liquid CO2 foams were generated and showed significant viscosity improvement compared to liquid CO2. The foams exhibited better filtration control performance compared to liquid CO2 and liquid CO2+N2 systems. Although the addition of HFE did not result in the formation of filter cake, the foam showed a wall-building behavior, which could be explained by the CO2 phase change in porous media. As foam quality increased from 28% to 92%, the leakoff coefficient and spurt loss volume first decreased until the foam became unstable and changed into mist flow. The leakoff coefficient of foam increased with the increase in permeability of porous media. For foam with the quality of about 50–80%, a change of 2 orders of magnitude in permeability resulted in a change of 1 order of magnitude in leakoff coefficient. At high pressure difference, lower initial quality foam (∼30%) showed better filtration performance than higher initial quality foam (∼80%). When the pressure difference was high enough to cause the CO2 phase change from liquid to gas in the porous media, the initial foam damage after filtration became obvious, but the damage could be eliminated with time by gas return flow. Thus, by using N2/liquid CO2 foam in porous media, the fluid filtration behavior could be controlled without damage.

Understanding aqueous foam with novel CO2-soluble surfactants for controlling CO2 vertical sweep in sandstone reservoirs

The ability of a novel nonionic CO2-soluble surfactant to propagate foam in porous media was compared with that of a conventional anionic surfactant (aqueous soluble only) through core floods with Berea sandstone cores. Both simultaneous and alternating injections have been tested. The novel foam outperforms the conventional one with respect to faster foam propagation and higher desaturation rate. Furthermore, the novel injection strategy, CO2 continuous injection with dissolved CO2-soluble surfactant, has been tested in the laboratory. Strong foam presented without delay. It is the first time the measured surfactant properties have been used to model foam transport on a field scale to extend our findings with the presence of gravity segregation. Different injection strategies have been tested under both constant rate and pressure constraints. It was showed that novel foam outperforms the conventional one in every scenario with much higher sweep efficiency and injectivity as well as more even pressure redistribution. Also, for this novel foam, it is not necessary that constant pressure injection is better, which has been concluded in previous literature for conventional foam. Furthermore, the novel injection strategy, CO2 continuous injection with dissolved CO2-soluble surfactant, gave the best performance, which could lower the injection and water treatment cost.

Effect of Foam on Liquid Phase Mobility in Porous Media

We investigate the validity of the assumption that foam in porous media reduces the mobility of gas phase only and does not impact the liquid-phase mobility. The foam is generated by simultaneous injection of nitrogen gas and a surfactant solution into sandstone cores and its strength is varied by changing surfactant type and concentration. We find, indeed, that the effect of foam on liquid-phase mobility is not pronounced and can be ignored. Our new experimental results and analyses resolve apparent discrepancies in the literature. Previously, some researchers erroneously applied relative permeability relationships measured at small to moderate capillary numbers to foam floods at large capillary number. Our results indicate that the water relative permeability in the absence of surfactant should be measured with the capillary pressure ranging up to values reached during the foam floods. This requires conducting a steady-state gas/water core flood with capillary numbers similar to that of foam floods or measuring the water relative-permeability curve using a centrifuge.

Investigation of foam flow in a 3D printed porous medium in the presence of oil

Foams demonstrate great potential for displacing fluids in porous media which is applicable to a variety of subsurface operations such as the enhanced oil recovery and soil remediation. The application of foam in these processes is due to its unique ability to reduce gas mobility by increasing its effective viscosity and to divert gas to un-swept low permeability zones in porous media. The presence of oil in porous media is detrimental to the stability of foams which can influence its success as a displacing fluid. In the present work, we have conducted a systematic series of experiments using a well-characterised porous medium manufactured by 3D printing technique to evaluate the influence of oil on the dynamics of foam displacement under different boundary conditions. The effects of the type of oil, foam quality and foam flow rate were investigated. Our results reveal that generation of stable foam is delayed in the presence of light oil in the porous medium compared to heavy oil. Additionally, it was observed that the dynamics of oil entrapment was dictated by the stability of foam in the presence of oil. Furthermore, foams with high gas fraction appeared to be less stable in the presence of oil lowering its recovery efficiency. Pore-scale inspection of foam-oil dynamics during displacement revealed formation of a less stable front as the foam quality increased, leading to less oil recovery. This study extends the physical understanding of oil displacement by foam in porous media and provides new physical insights regarding the parameters influencing this process.

Effect of temperature on foam flow in porous media

Foam can increase sweep efficiency within a porous medium, which is useful for oil-recovery processes [1]. The flow of foam in porous media is a complex process that depends on properties like permeability, porosity and surface chemistry, but also temperature. Although the surface activity of surfactants as a function of temperature is well described at the liquid/liquid or liquid/gas interface, data on the effect of temperature on foam stability is limited, especially in porous media.In this work, we tested a surfactant (AOS) at different temperatures, from 20°C to 80°C, in a sandstone porous medium with co-injection of foam. The pressure gradient, or equivalently the apparent viscosity, was measured in steady-state experiments. The core-flood experiments showed that the apparent viscosity of the foam decreased by 50% when the temperature increased to 80°C. This effect correlates with the lower surface tension at higher temperatures. These results are compared to bulk foam experiments, which show that at elevated temperatures foam decays and coalesces faster. This effect, however, can be attributed to the faster drainage at high temperature, as a response to the reduction in liquid viscosity, and greater film permeability leading to faster coarsening.Our results using the STARS foam model show that one cannot fit foam-model parameters to data at one temperature and apply the model at other temperatures, even if one accounts for the change in fluid properties (surface tension and liquid viscosity) with temperature. Experiments show an increase in gas mobility in the low-quality foam regime with increasing temperature that is inversely proportional to the decrease in gas-water surface tension. In the high-quality regime, results suggest that the water saturation at which foam collapses fmdry increases and Pc* decreases with increasing temperature.

The flow of a foam in a two‐dimensional porous medium

AbstractFoams have been used for decades as displacing fluids for enhanced oil recovery and aquifer remediation, and more recently, for remediation of the vadose zone, in which case foams carry chemical amendments. Foams are better injection fluids than aqueous solutions due to their low sensitivity to gravity and because they are less sensitive to permeability heterogeneities, thus allowing a more uniform sweep. The latter aspect results from their peculiar rheology, whose understanding motivates the present study. We investigate foam flow through a two‐dimensional porous medium consisting of circular obstacles positioned randomly in a horizontal transparent Hele‐Shaw cell. The local foam structure is recorded in situ, which provides a measure of the spatial distribution of bubble velocities and sizes at regular time intervals. The flow exhibits a rich phenomenology including preferential flow paths and local flow nonstationarity (intermittency) despite the imposed permanent global flow rate. Moreover, the medium selects the bubble size distribution through lamella division‐triggered bubble fragmentation. Varying the mean bubble size of the injected foam, its water content, and mean velocity, we characterize those processes systematically. In particular, we measure the spatial evolution of the distribution of bubble areas, and infer the efficiency of bubble fragmentation depending on the various control parameters. We furthermore show that the distributions of bubble sizes and velocities are correlated. This study sheds new light on the local rheology of foams in porous media and opens the way toward quantitative characterization of the relationship between medium geometry and foam flow properties. It also suggests that large‐scale models of foam flows in the subsurface should account for the correlation between bubble sizes and velocities.

Transport of Nanoparticle-Stabilized CO $$_2$$ 2 -Foam in Porous Media

Foam is injected in the subsurface to improve mobility control through the increase in the effective gas viscosity, e.g., in CO $$_2$$ -based enhanced oil recovery processes. As fine-textured foam has higher viscosity, it is envisaged to achieve an optimal foam texture and to maintain it for the entire period of an application. However, mechanisms of foam formation and destruction, which affect texture, are difficult to regulate. In this study, we investigate the synergic effect of nanoparticles and surfactant on the foam texture and the effective gas viscosity ( $$\mu _g^f$$ ) during transport in a porous medium. Experiments using glass-bead packs were performed injecting CO $$_2$$ and a solution containing either only surfactant or surfactant and nanoparticles. During each experiment, the pressure drop ( $$\Delta p$$ ) through the porous medium was measured to follow the generation of the foam. A two-phase flow mechanistic model combining the mass conservation law for water and CO $$_2$$ and the population balance equation of the lamellae was implemented to analyze the experiments and predict foam transport under the investigated conditions. The constitutive equations for foam generation and destruction were based on the dominant role of pressure gradient on lamella division and of capillary pressure on bubble coalescence, and their parameters were estimated using pressure drop measurements. Both equations were formulated for a surfactant-stabilized foam, and it was the aim of this work to understand their validity also for the case of a nanoparticle-stabilized foam. The experiments compare well with the theory showing that a foam stabilized with nanoparticles and surfactant can be modeled as a surfactant-stabilized foam. Overall, $$\Delta p$$ increases smoothly while the foam forms and, upon breakthrough, it stabilizes around a constant value while approaching steady state. During this phase, oscillations occur, particularly when high-quality foam is generated as the system is close to its critical conditions of capillary pressure and water saturation. When steady state is reached, the effective gas viscosity varies with $$f_g$$ and solution composition and significantly increases when surfactant and nanoparticles are added. The maximum value of $$\mu _g^f$$ is 0.110 Pa s for $$f_g$$ = 0.75, which is almost twofold of the maximum value attained when only a surfactant is used, corresponding to 0.067 Pa s at $$f_g$$ = 0.4. This suggests that when nanoparticles and surfactant are employed, they can favor the formation of a strong high-quality CO $$_2$$ -foam.

Fundamental investigation of foam flow in a liquid-filled Hele-Shaw cell

The relative immobility of foam in porous media suppresses the formation of fingers during oil displacement leading to a more stable displacement which is desired in various processes such as Enhanced Oil Recovery (EOR) or soil remediation practices. Various parameters may influence the efficiency of foam-assisted oil displacement such as properties of oil, the permeability and heterogeneity of the porous medium and physical and chemical characteristics of foam. In the present work, we have conducted a comprehensive series of experiments using customised Hele-Shaw cells filled with either water or oil to describe the effects of foam quality, permeability of the cell as well as the injection rate on the apparent viscosity of foam which is required to investigate foam displacement. Our results reveal the significant impact of foam texture and bubble size on the foam apparent viscosity. Foams with smaller bubble sizes have a higher apparent viscosity. This statement only applies (strictly speaking) when the foam quality is constant. However, wet foams with smaller bubbles may have lower apparent viscosity compared to dry foams with larger bubbles. Furthermore, our results show the occurrence of more stable foam-water fronts as foam quality decreases. Besides, the complexity of oil displacement by foam as well as its destabilizing effects on foam displacement has been discussed. Our results extend the physical understanding of foam-assisted liquid displacement in Hele-Shaw cell which is a step towards understanding the foam flow behaviour in more complex systems such as porous media.

Mechanistic study on foam lamellae flow characteristics in tubes

For understanding foam propagation behaviour in porous media, experimental investigations were carried out concerning lamellae foam flow characteristics in a vertical tube. Foam is treated as a two-phase fluid, and the governing non-dimensional parameters were obtained through theoretical analysis. Two types of foams, CO2 and N2 foams, were studied and clear linear relationships between non-dimensional parameters of Δpd/σ and (3μU/σ)2/3 were observed. With different threshold values, the experimentally obtained mechanistic models for both foams predict much higher flow resistance compared with present popular models. Experimental results reveal the fact that a startup pressure is necessarily needed for mobilising the foam lamellae, and therefore indicate that the Herschel–Bulkley model instead of the power-law model could be better in revealing the mechanism of flowing foams in porous media in large scale.

Modeling Techniques for Foam Flow in Porous Media

Summary Foam, a dispersion of gas in liquid, has been investigated as a tool for gas-mobility and conformance control in porous media for a variety of applications since the late 1950s. These applications include enhanced oil recovery, matrix-acidization treatments, gas-leakage prevention, as well as contaminated-aquifer remediation. To understand the complex physics of foam in porous media and to implement foam processes in a more-controllable way, various foam-modeling techniques were developed in the past 3 decades. This paper reviews modeling approaches obtained from different publications for describing foam flow through porous media. Specifically, we tabulate models on the basis of their respective characteristics, including implicit-texture as well as mechanistic population-balance foam models. In various population-balance models, how foam texture is obtained and how gas mobility is altered as a function of foam texture, among other variables, are presented and compared. It is generally understood that both the gas relative permeability and viscosity vary in the reduction of gas mobility through foam generation in porous media. However, because the two parameters appear together in the Darcy equation, different approaches were taken to alter the mobility in the various models: only reduction of gas relative permeability, increasing of effective gas viscosity, or a combination of both. The applicability and limitations of each approach are discussed. How various foam-generation mechanisms play a role in the foam-generation function in mechanistic models is also discussed in this review, which is indispensable to reconcile the findings from different publications. In addition, other foam-modeling methods, such as the approaches that use fractional-flow theory and those that use percolation theory, are also reviewed in this work. Several challenges for foam modeling, including model selection and enhancement, fitting parameters to data, modeling oil effect on foam behavior, and scaling up of foam models, are also discussed at the end of this paper.

Numerical Calculation of Transient Flow of Polymer Foam in Porous Media

Based on the mathematical model of one dimension transient flow of the polymer foam in porous media, the numerical calculation method of the flow mentioned above by using the finite difference method is given. Through the experiments of one dimension transient flow of HPAM (Hydrolytic Polyacrylamide) foam in the artificial sandstone core, the HPAM foam generation and coalescence coefficient of the mathematical model mentioned above are determined. The profiles of the liquid phase saturation, the pressure drop and the number density of one dimension transient flow of HPAM foam with the dimensionless time in artificial sandstone core are numerically calculated and analyzed by using the numerical calculation method.

Polymer Foam Flow in Porous Media under Different Injection Modes

The mathematical models of the flow of polymer foam in porous media under three injection modes are established and the relevant numerical calculation methods are given. The profiles of the liquid phase saturation, the pressure drop and the number density of the flowing HPAM foam in artificial sandstone cores with the dimensionless distance under three injection modes are numerically calculated and analyzed. The results show that, compared with the injection mode 2 and 3, HPAM foam flows in a piston-like fashion in the artificial sandstone core under the injection mode 1 and produces the biggest pressure drop. Obviously, the flood efficiency is the highest under the injection mode 1.

Effect of Gas Diffusion on Mobility of Foam for Enhanced Oil Recovery

Diffusion of gas across liquid films between bubbles is thought to increase average bubble size in foam in porous media. It is cited as one reason why $$\hbox {CO}_{2}$$ foams for enhanced oil recovery (EOR) are less resistant to flow than $$\hbox {N}_{2}$$ foams and why mixing $$\hbox {N}_{2}$$ with steam increases the resistance of steam foam. In porous media, diffusion can rapidly destroy bubbles smaller than a pore, but in EOR foam bubbles are thought to be larger than pores. This study examines the effect of inter-bubble gas diffusion on flowing bubbles in a periodically constricted tube and, in particular, its effect on the bubble-size distribution and capillary resistance to flow. The study is based on the solution for bubble shapes, curvatures, and pressure differences between bubbles from previous studies of bubble movement through periodically constricted tubes. It uses these results to estimate the diffusion rate between bubbles. Bubbles somewhat smaller than a pore can indeed disappear by diffusion as the bubbles move. For bubbles larger than a pore, as expected in EOR, diffusion does not affect bubble size. Instead, diffusion actually increases capillary resistance to flow, because lamellae spend more time in positions where lamella curvature resists forward movement. When fit to pressures and diffusion and convection rates representative of field application of foams, diffusion is not expected to alter the bubble-size distribution in a foam. Instead it modestly increases the resistance to flow. The reason for the apparent weakness of $$\hbox {CO}_{2}$$ foam therefore evidently lies in factors other than $$\hbox {CO}_{2}$$ ’s large diffusion rate through foam.

Mathematical Model of Foam Flowing Characteristics by Snap-Off Mechanisms at Steady State in Porous Media

Flow characteristics and regeneration processes of foams were influenced by lamella properties and pore-throat structure in porous media. In this article, porous media was simplified as a bunch of constricted capillary tubes according to grain size, pore-throat radius, and immobile water saturation in porous media. Based on an analysis of forces upon liquid lamella, a mathematical model of foam migration and regeneration at steady state was established according to the mass conservation law and the momentum conservation law in porous media. The model could be used to calculate some important parameters in porous media, such as pressure distribution, shearing stress, lamella morphology, liquid-layer thickness, regeneration bubble size, etc. A series of flow experiments were carried out to investigate the influence of liquid properties and pore-throat structure on flow characteristics and resistance behavior of foams in porous media. The experimental results showed that pressure distribution monotonously decreased along porous media. The theoretical results were in good agreement with the experimental results. Foam structure, that is, foam quality was an important factor upon foam resistance behavior in porous media. The strongest resistance ability of foams was achieved at foam quality of 85% in porous media.

Pressure Difference for Moving Nitrogen Bubbles in a Waving Duct

A duct with varying cross-sections can show some essential features of the motion of foam in porous media. In this paper, the effective viscosity of the bubbles train moving through cylindrical ducts with sinusoidal cross-section was experimentally measured. The test tube has total length of 1.14 m and has constrictions at interval of 0.0095 m. It is found that the foam effective viscosity is much higher than water viscosity and it is possible to extend the foam rheology correlations in constant cross section ducts to predict the flow differences in waving ducts.

Image Analysis of a Moving Bubble Train in a Tube

A tube with varying cross sections can capture some essential features of the motion of foam in porous media. In this paper, experiments were carried out concerning a moving bubbles train through cylindrical ducts with sinusoidal cross-section. The test tube has total length of 1.14 m and has constrictions at interval of 0.0095 m. The visual images of a single lamella motion were recorded and were interpreted. It is found the lamella decelerates in the diverging portion while accelerates in the converging part of the tube.

Stability Comparison Between Particles-Stabilized Foams and Polymer-Stabilized Foams

The enhanced oil recovery (EOR) results of foam flooding depend largely on the stability of foam flow within porous reservoirs. To stabilize foams, polymers such as partially hydrolyzed polyacrylamide are often introduced into the foaming agent. However, particles-stabilized foams have been paid more attentions in recent years. To investigate the better stabilizer for foam application in EOR, experimental stability comparison between polymer-stabilized foams and clay particles-stabilized foams was investigated. To do this, the static stability of bulk foams was studied by half-life of foams and rheological behavior of foaming agent solution. The dynamic stability of two types of compressed foams in porous media was then compared with blocking ability. Results showed that particles-stabilized bulk foams were more stable than polymer-stabilized bulk foams, and the viscoelasticity of surfactant-particles solution was higher. Moreover, blocking ability of particles-stabilized foams was also better than that of polymer-stabilized ones.