Foam In Porous Media Research Articles

Fractional Flow Analysis of Foam Displacement in Tight Porous Media with Quasi-Static Pore Network Modeling and Core-Flooding Experiments

Fractional flow analysis is an efficient tool to evaluate the gas-trapping performance of foam in porous media. The pore-scale simulation study and the core-scale experimental work have been bridged via the fractional flow analysis to distinguish the characteristics of foam displacement inside the tight porous media with varying absolute permeability, injection rate, and foam quality. In this work, the combined investigation suggests that conventional foam-enhancing strategies, pursuing higher foam quality and stronger foam regime, are inefficient and restricted in tight reservoirs that the critical Sw corresponding to the limiting capillary pressure has increased around 37~43%, which indicates severely weakened gas-trapping capacity as permeability reduces one order of magnitude. The moderate mobility adjustment and corresponding optimized fluid injectivity exerting from the “weak foam” flow presents a staged decline feature of decreasing water fractional flow, which implies the existence of the delayed gas-trapping phenomenon when water saturation reduces to 0.5~0.6. The finding has supported the engineering ideal of promoting low-tension gas (LTG) drive processes as a potential solution to assist field gas injection applications suffering from gas channeling. Also, the validation with core-flooding experimental results has revealed several defects of the current pore network model of foam displacement in tight porous media, including exaggerated gas trapping and overestimated confining water saturation. This study has innovatively demonstrated the feasibility and potential of optimizing the foam performance of gas trapping and mobility control in tight reservoirs, which provides a clue that may eventually boost the efficiency of the gas injection process in enhanced oil recovery or CO2 sequestration projects.

Flow Behavior and Mechanism Insights into Nanoparticle-Surfactant-Stabilized Nitrogen Foam for Enhanced Oil Recovery in the Mature Waterflooding Reservoir.

To solve the problem of poor stability and low enhanced oil recovery efficiency of conventional foam, nanoparticle-surfactant-stabilized nitrogen foam was prepared, and the influence of temperature, salinity, oil content, and pressure on foam performance was systematically investigated. Then, the flow behavior of conventional foam and nanoparticle-surfactant-stabilized foam in porous media was studied. Parallel sand pack flooding and visualization microflooding experiments were performed to investigate the enhanced oil recovery ability of nanoparticle-surfactant-stabilized foam from core-scale to pore-scale. Results showed that the nanoparticles can improve foam performance. When the temperature increases from 60 to 100 °C, the foam volume and foam half-life of nanoparticle-surfactant-stabilized foam decrease by 20 and 36%, respectively. The nanoparticle-surfactant-stabilized foam has a good salt resistance. The oil content limit value of the foam performance is 15%. With the increase of pressure, the foaming performance and foam stability are enhanced obviously. Compared with conventional surfactant-stabilized foam, the nanoparticle-surfactant-stabilized foam can have better plugging and expansion of the swept volume capacity. The micromodel flooding results are consistent with the parallel sand pack flooding results. Compared with conventional surfactant stabilized foam, nanoparticle-surfactant-stabilized foam has better enhanced oil recovery ability than conventional surfactant-stabilized foam due to its higher foaming ability, foam stability, and sweep efficiency improvement ability.

Experimental study on the effect of foam in preventing gas channeling in shale reservoir

Shale oil resources have enormous potential and broad development prospects in China. Especially with the rapid development of horizontal well volume fracturing technology, the production of shale oil has been greatly increased, and it has become an important position to increase oil and gas storage and production. However, due to the existence of artificial and natural fractures produced by fracturing, gas channeling will occur in the process of huff-n-puff gas injection, which will affect the production and lead to poor development effect. In this paper, foam is used as an anti-channeling agent in the process of huff-n-puff gas injection. The results of microfluidic experiments show that the production mode of foam in porous media is liquid membrane hysteresis and liquid membrane separation. In porous media, foam first blocks large channels such as fractures, and then enters the matrix. The oil recovery mechanism of foam assisted gas injection in porous media is to improve the sweep efficiency and oil displacement efficiency of gas. Compared with N2 huff-n-puff, the oil recovery of the first cycle of foam assisted N2 huff-n-puff increased by 4.50%, and the third cycle increased by 9.58%. It is proved that foam has good anti channeling effect in gas huff-n-puff injection process. The research results provide an effective method for efficient gas injection development of shale oil.

Surfactant transport upon foam films moving through porous media

In the context of foam improved oil recovery or foam-based soil/aquifer remediation, a model is presented for evolution of surfactant surface concentration on foam films moving through porous media. The model exploits an analogy between surface transport behaviour in foam fractionation and surfactant transport behaviour for foam in porous media. Films either stretch as they move from pore throat to pore body, or shrink when moving from pore body to pore throat: this stretching/shrinking then influences surfactant concentration. In addition, Plateau borders at the edges of films can supply surfactant to films, or receive surfactant from them. The model is solved numerically and key parameters governing its behaviour are identified. Parameter regimes are encountered, corresponding to modest stretching or shrinkage rates, in which surfactant concentration on films is predicted to be closely coupled to surfactant concentration in Plateau borders. Alternate parameter regimes are encountered, corresponding instead to fast stretching or shrinkage rates, in which surfactant concentration on films is predicted to become independent of surfactant concentration in Plateau borders. Asymptotic solutions available in each of these regimes are compared with numerical solutions. A preliminary comparison between the model predictions and experimental data from literature is also described. The appeal of the model is that predictions can be made comparatively simply. Indeed the model can predict when foam films might become significantly depleted in surfactant, possibly leaving films liable to breakage, which would then be detrimental to foam in porous media applications.

Factors influencing the mobility control ability of diutan gum‐enhanced foam in porous media

AbstractDiutan gum (DG) is an anionic polysaccharide produced by Sphingomonas sp. ATCC 53159. The DG‐enhanced foam (DGEF) formed by the DG and foam has great application potential in enhanced oil recovery. In this research, the influence of injection parameters on DGEF was studied by conducting orthogonal experiment, with residual resistance coefficient (Rff) as the main evaluation index. The micro‐state of the foam was observed using an etching model and scanning electron microscope. The mechanism of different factors on the mobility control ability of the foam was discussed based on the apparent viscosity and surfactant depletion. The results show that the Rff of foam is correlated with the apparent viscosity, and the foam with high apparent viscosity had a good flow control ability. The calculation of the surfactant depletion shows that the bubble stability decreased significantly when the concentration of Sodium alpha‐olefin sulfonate (AOS) cannot meet the minimum stabilization concentration, thus weakening the mobility control ability. Based on the study of crude oils, the presence of oil phase will seriously weaken the mobility control ability of DGEF, but the effect of oil with higher content of resin and asphaltene will be relatively weak.

Mechanism of enhanced oil recovery of ultra-dry CO2-in-water foams in porous media: Experiments and numerical simulation

The application of ultra-dry CO2 foam in enhanced oil recovery (EOR) accelerates recovery and enables CO2 utilization and sequestration. The flow characteristics of foam in porous media play a crucial role in the foam EOR process. Herein, ultra-dry CO2-in-water (C/W) foam with 10% water was prepared at 80 °C and 12 MPa using cocamidopropyl betaine (CAPB) and nonionic polyacrylamide (NPAM). Additionally, the constitutive equation for the foam fluid was determined by flow experiments using tubes with different diameters. The CO2 foam was a shear-thinning, non-Newtonian fluid and conformed to the Herschel–Bulkley (H–B) model. The core displacement experiment with the permeability of 470 mD showed that the oil recovery of foam flooding increased from 56.01% of water flooding to 76.01% at the same temperature and pressure. The maximum pressure difference rose sharply from 0.48 MPa of water flooding to 1.2 MPa of foam flooding, increasing by 2.5 times; the pressure difference finally stabilized at 0.64 MPa, which was approximately 4.3 times that of water flooding. Moreover, a two-dimensional (2D) model of the porous media was constructed using digital core technology. Using the validated model, sensitivity analysis based on the phase-field method (PFM) was performed to investigate the effect of different power-law exponents on displacement. The results indicate that increasing the power-law exponent of the foam fluid slowed down breakthrough and improved the sweep efficiency, resulting in higher oil recovery.

A systematic investigation of the relationship between properties of bulk foam and foam in porous media

Bulk foam analysis (static test) is simple and fast, which makes it a cost-effective method for screening and ranking hundreds of surfactants being considered for foam applications. Coreflood tests (dynamic test) can also be used, but it is quite laborious and costly. However, previous reports show that ranking based on static tests sometimes differs from ranking based on dynamic tests. To date, the reason for such a discrepancy is not well understood. Some believe that it may be due to faulty experimental design while some others believe that there is no discrepancy if the right foam performance indices are used to describe and compare the results from both methods. For the first time, this study reports a systematic series of static tests conducted on different foaming solutions (with surfactant concentration ranging from 0.025 to 5 wt%) and duplicated in dynamic tests using the same core sample for all the surfactant solutions. The dynamic test was also repeated on three different rocks of a wide permeability range (26–5000 mD) for each of the surfactant solutions. Unlike previous studies, here multiple dynamic foam indices (limiting capillary pressure, apparent viscosity, trapped foam, and trapped to mobile foam ratio) were measured and compared with the performance indices measured from the static tests (foam texture and foam half-life). Dynamic tests were in total agreement with static tests for all the foam formulations. However, it was observed that the pore size of the base filter disk used in the static foam analyzer can be a potential source of conflicting results when comparing with dynamic test. This is because a threshold pore size exists above which some foam properties (apparent viscosity and trapped foam) significantly decreased compared to the properties before that threshold. Foam limiting capillary pressure is the only foam property that does not show such a trend. It also appears that such threshold occurs above a certain surfactant concentration (0.025 wt%). Apparently, it becomes imperative that the pore size of the filter disk used in the static test and the porous medium used in dynamic tests must be on the same side of the threshold point, otherwise there may be disparity in their results. The threshold surfactant concentration should also be determined. The role of these two factors (pore size and surfactant concentration) requires further investigation.

EXPERIMENTAL INVESTIGATION ON FRACTAL CHARACTERIZATION OF IN-SITU FOAM IN POROUS MEDIA

The in-situ foam technology has been extensively applied in the complex reservoir reconstruction since it improves the sweep efficiency by diverting the flow of injected fluids into areas with lower permeability and as a result enhances the oil recovery. The in-situ foam structure inside the pores can significantly affect the sweep efficiency, however, quantitative characterizations on foam structure are inadequate. Here, we propose a quantitative method based on fractal theory and the two-dimensional (2D) micro physical simulation experiment for the study of fractal characteristic, evolution law and sensitivity analysis. The findings demonstrate that foam confined within porous media exhibits fractal characteristics, as evidenced by the measured box-counting fractal dimensions ranging between 1.05 and 1.752 based on acquired structural images. Notably, a higher fractal dimension corresponds to a more irregular in-situ foam structure. Besides, in-situ foam in the porous media presents the “quasi check sign” evolution law, which can be divided into three time-dependent stages. Moreover, the evolution laws of in-situ foam within porous media remains consistent across varying temperatures and concentrations of foaming agents, and increasing temperature and decreasing concentration can shorten the time to reach the inflection point.

Foam placement for soil remediation: scaling foam flow models in heterogeneous porous media for a better improvement of sweep efficiency

If injected with a large gas fraction, foam reduces mobility more in high-permeability layers and diverts flow to low-permeability layers. Here is a qualitative statement that has been claimed many times in many works related to environmental remediation and oil recovery. It is so true and relevant for foam flow in porous media and yet so little quantified and even less exploited in Darcy-scale numerical simulation. After briefly reviewing opportunities and challenges related to the use of foams in porous media and its Darcy-scale implicit-texture and population-balance modelling, we make a detour out of the strict framework of mathematical models by revisiting with a fresh eye the physics of foams on the large scale of heterogeneous natural porous media in terms of scaling laws. Specifically, it has been recently shown experimentally and theoretically that foam mobility reduction scales approximately as the square root of rock permeability within the framework of Darcy-type implicit-texture foam flow models [Douarche et al. (2020) Scaling foam flow models in heterogeneous reservoirs for a better improvement of sweep efficiency (Paper ThB04), in:17th European Conference of the Mathematics of Oil Recovery (ECMOR), Edinburgh, Scotland, 14–17 September; Gassara et al. (2020) Trans. Porous Media 131, 1, 193–221]. This also appears to hold for population-balance models under the local steady state assumption. This quantitative scaling law for the effect of permeability on foam properties was inferred from an analogy between foam flow in porous media and foam flow in capillary tubes and was found consistent with the modelling of available experimental data. We demonstrate by varying the permeability contrast and anisotropy of a stack of porous layers how foam regulates the flow and leads to flow diversion from high- to low-permeability layers. The threshold in permeability heterogeneity for which such a foam-driven diversion becomes effective is quantified through a sensitivity study accounting for foam injection type, permeability heterogeneity and anisotropy, heterogeneity structure, and scaling procedure. The simulations carried out clearly indicate that ignoring mobility reduction dependence on permeability in the foam process assessment of heterogeneous formations leads to an underestimation of mobility reduction benefits to improve flow conformance. The question of cores selection, as this rock-typing strategy in relation to the porous medium characterization may guide a smart and optimal design of pre-feasibility laboratory campaign for foam evaluation, and the generalization of the findings to multi-facies geological formations are also discussed. As such, the use of physical foam mobility reduction scaling law is highly recommended for foam process evaluation.

Flow characteristics and regime transition of aqueous foams in porous media over a wide range of quality, velocity, and surfactant concentration

Aqueous foam is broadly applicable to enhanced oil recovery (EOR). The rheology of foam as a function of foam quality, gas and liquid velocities, and surfactant concentration constitute the foundation of its application. The great variations of the above factors can affect the effectiveness of N2 foam in EOR continuously in complex formations, which is rarely involved in previous relevant studies. This paper presents an experimental study of foam flow in porous media by injecting pre-generated N2 foam into a sand pack under the conditions of considering a wide range of gas and liquid velocities and surfactant concentrations. The results show that in a wide range of gas and liquid velocities, the pressure gradient contours are L-shaped near the coordinate axes, but V-shaped in other regions. And the surfactant concentration is a strong factor influencing the trend of pressure gradient contours. Foam flow resistance is very sensitive to the surfactant concentration in both the high- and low-foam quality regime, especially when the surfactant concentration is less than CMC. The foam quality is an important variable to the flow resistance obtained. There exists a transition point from low- to high-quality regime in a particular flow system, where has the maximum flow resistance, the corresponding foam quality is called transition foam quality, which increases as the surfactant concentration increases. The results can add to our knowledge base of foam rheology in porous media, and can provide a strong basis for the field application of foams.

Dynamic Behaviors and Mechanisms of Air-Foam Flooding at High Pressure and Reservoir Temperature via Microfluidic Experiments.

Air injection has been proven to be an effective improved oil recovery technique for deep and light oil reservoirs with low permeability and poor water injectivity. But the efficiency of air injection in highly heterogeneous reservoirs is low due to poor gas sweeping that may lead to early oxygen breakthrough caused by gas channeling and viscous fingering. Foam can be used to assist air injection to overcome the obstacles of early gas breakthrough and to increase the displacement and sweeping efficiency. In this paper, laser-etched visual microscopic pore models were used as microfluidic devices to study the air-foam flooding process in porous media at reservoir temperature and high pressure. The dynamic behaviors and relevant mechanisms of air-foam flooding were investigated. Typical mechanisms of foam generation in porous media are achieved in different parts of the micromodel, which can be listed as follows: lamella leave-behind, lamella division, and snap off. Analysis on flow states of air foam showed that foams migrate in porous media by bursting and regenerating during the flooding process. It can be observed that the flow mode of foam in porous media is the separate flow of gas and liquid through microscopic displacement experiments, suggesting that foam should not be treated as a homogeneous phase in heterogeneous porous media. The pressing, occupying, and selective blocking effects of foam in porous media exhibited different oil displacement performances with the presence of various pore geometries and networks. Tiny foams also showed stripping and carrying effects on larger oil droplets benefiting from the lipophilicity of foam. Through comprehensive analysis on overall and local oil displacement mechanisms, air-foam injection could enhance the microscopic sweep volume and improve the oil displacement efficiency.

Yield stress of foam flow in porous media: The effect of bubble trapping

Foam behaves as a yield-stress fluid as it flows in a porous medium. Quasi-static analysis suggests that the yield stress arises from the non-smooth motion of foam films, denoted as lamellae, in pores. In order to study the effect of trapped lamellae on the motion of a moving lamella and consequently on the yield stress of foam, we conduct numerical simulations in the quasi-static limit. We propose a new method utilizing the surface energy minimization algorithm, which explicitly considers the connectivity of pores in a porous medium. We consider two different shapes of pore and vary the number of nearby trapped lamellae to investigate the effects of bubble trapping on the non-smooth and the smooth motion of a single lamella passing through a pore, respectively. We find that the trapped lamellae lead to the increased volume-averaged pressure drop and thus the increased yield stress. Notably, the motion of a lamella through a pore with rounded corners in the pore body becomes non-smooth, due to the presence of trapped lamellae. The results contribute to a better understanding of the yield stress of foam in porous media.

Pore-scale bubble population dynamics of CO2-foam at reservoir pressure

The flow of CO2 foam for mobility control in porous media is dictated by the foam texture, or bubble density, which is commonly expressed as the number of bubbles per unit of flowing gas. In most high-pressure laboratory studies of foam in porous media, the local foam texture cannot be determined due to opaque flow systems. Here, we unlock real-time foam texture dynamics at high pressure (100 bar) by utilizing a realistic pore network with an extended field of view. We identified snap-off as the dominant foam generation mechanism, with additional fining of foam texture caused by backward foam propagation. Foam coalescence during continuous CO2 injection resulted in large gas channels parallel to the general flow direction that reduced the overall foam apparent viscosity. A large fraction of the CO2 foam remained trapped (Xt > 0.97) and stationary in pores to divert CO2 flow and increase sweep efficiency. The gas mobility was calculated from the fraction of trapped bubbles at the pore-scale, and the apparent foam viscosity agreed with similar injection test performed at core-scale. Hence, improved understanding of CO2 foam texture evolution (nf) can strengthen the validation of numerical foam models for upscaling of flow phenomena, instrumental in the development of field scale implementation of CO2 foam for in carbon utilization and storage applications.

A Graphical Interpretation Technique to Evaluate Strength and Stability of Foam in Porous Media Based on Mobile-Trapped Foam Ratio

A Graphical Interpretation Technique to Evaluate Strength and Stability of Foam in Porous Media Based on Mobile-Trapped Foam Ratio

Measuring and modeling nanoparticle transport by foam in porous media

In this paper, an experimental study of nanoparticle transport by foam is presented. Bubbles made of N2-gas were stabilized with either a cationic surfactant (Cetyl Trimethyl Ammonium Bromide, CTAB), silica nanoparticles, or a combination of them. The concentrations of the surface active materials were selected upon foamability and stability tests. Column-flood tests were run until steady-state changing nanoparticle concentration, foam quality (fg), and flow rate. A synergistic behaviour of surfactant and nanoparticles help the formation of a strong foam. The measurements were used to validate a mechanistic model, presented in our earlier work (Li and Prigiobbe, 2020), which couples foam and nanoparticles transport with agglomeration and extended-DLVO theory. The model agrees well with the measurements and results show that an high-quality (ca. 90% gas fraction) can be used to carry nanoparticles and the efficient increases with flow velocity. This opens the opportunity for the application of foam as a carrier of nanoparticles in subsurface applications such as the remediation of contaminated sites and makes the model a valuable tool to design and predict such operations.

Foam-Assisted Water–Gas Flow Parameters: From Core-Flood Experiment to Uncertainty Quantification and Sensitivity Analysis

Uncertainty quantification and sensitivity analysis are crucial tools in the development and evaluation of mathematical models. In enhanced oil recovery, the co-injection of foam in porous media has been investigated through laboratory experiments and mathematical models as a promising technique for improving sweep efficiency. In this work, we study two mathematical models of foam flow in porous media. First, we present a foam quality-scan experiment using nitrogen and low concentration of an alpha-olefin sulfonate surfactant in brine using Indiana limestone carbonate core. Second, we evaluate the models based on their ability to represent the experimental data using inverse uncertainty quantification techniques. Third, the parameters’ estimated distributions are used to perform both forward uncertainty quantification and sensitivity analysis. We also present a detailed comparison of the models, and analyses on the experimental data, model discrepancy, and sources of uncertainties. The experimental results of foam apparent viscosity in carbonate rocks are consistent with other experiments in sandstones: The foam quality transition is present; the difference in apparent viscosity values is of the same magnitude as the difference in permeability. Propagation of uncertainties from the estimated parameter distributions through the models showed a good match between experimental data and model predictions. The sensitivity analysis showed that the model’s parameters play different roles and depend on the quantity of interest, the foam quality regime, and limiting water saturation. To summarize, this study provides essential information for possible improvements in the experiments and mathematical models of foam flow in EOR processes.

Experimental and numerical upscaling of foam flow in highly permeable porous media

Foam in porous media has been studied as a tool for various applications. Recently, the technology has become relevant for contaminated-aquifer remediation, where porous media are highly permeable. Therefore, the behavior of foam flow in high permeability porous media still raises numerous questions. In particular, upscaling of the foam flow from pore to Darcy scale is still under debate. Since the behavior of bulk foam has been studied principally in the food and cosmetics industries, and foam flow in porous media has mainly been investigated in the oil industry, the link between bulk-foam behavior and foam flow in porous media is still missing. The upscaling of foam flow from the pore scale to the laboratory scale could give valuable insight for understanding foam flow in aquifers.We studied the behavior of pre-generated foam with different foam qualities through the rheological characterization of bulk foam using a rheometer and also when flowing in a porous medium composed of 1 mm glass beads. Foam was formed by co-injecting surfactant solution and nitrogen gas through a porous column filled by fine sand. The homogenization method is used to study macroscopic foam flow properties in porous media by solving the non-linear boundary value problem. The rheology of bulk foam is then used as an input in the upscaling procedure for foam flow in different periodic model 2D and 3D unit cells.From our experiments, we found that the bulk foam is a yield-stress fluid and that the yield-stress values increase with foam quality. Moreover, the rheology of bulk foam corresponds well to the yield stress (Herschel-Bulkley-Papanastasiou) model. We found that foam behaves as a continuous yield-stress fluid in highly permeable porous media. It was also shown that the apparent foam viscosity in porous media increases with the foam quality at the same total flow rate. The results obtained from the rheometer successfully match the outcomes of apparent foam viscosity obtained by flow in porous media by a shifting parameter for the same foam quality. The apparent foam viscosity found in 1 mm glass-bead packing was much higher than bulk foam viscosity.Experimental results were compared to numerical results on simple unit cells. Although we observed considerable differences between the experimental and numerical results of upscaling, the general trend was identical. The differences can be explained by the complexity of the foam flow in porous media, especially foam compressibility. We found that foam flow at low capillary numbers is influenced by the trapping effect and at high pressure gradients by the compressibility. Compressibility was estimated for foam flow in 1 mm glass-bead packing. When foam compressibility is insignificant, the upscaling model can predict foam-flow behavior well at the Darcy scale.

Yield stress fluid behavior of foam in porous media

We report a local analysis of the flow of foams in two dimensional heterogeneous model porous media. Pressure measurements are combined with direct observation in order to determine simultaneously the effective viscosity and the fraction of trapped gas. Experiments are conducted in the low-quality regime, in a large range of capillary numbers and relative gas flow rates. The effective viscosity is very high (up to a few thousands times that of water) at low capillary numbers and rheology can be described by a decreasing power-law function of the capillary number of exponent ranging from -1 to -0.75. The flow is heterogeneous and the fraction of preferential paths increases with relative gas flow rate. However, increase in fraction of preferential paths remains very limited for increasing capillary number, thus failing to account for the strongly shear thinning behavior observed. Additional experiments motivated by this finding, carried out in a straight channel of varying cross-section, show a deviation from Bretherton law at low capillary numbers in this geometry with the bubble train behaving as a shear-thinning yield stress fluid. The pressure threshold evidenced accounts quantitatively for the effective viscosity data in the micromodel, indicating that it is the main mechanism underlying the measured foam rheology.

CO2 mobility reduction using foam stabilized by CO2- and water-soluble surfactants

Foam can reduce CO2 mobility to improve the sweep efficiency during injection into subsurface geological formations for CO2 storage and enhanced oil recovery. However, CO2 foams are thermodynamically unstable, so they must be stabilized. Surfactants are often used to generate and stabilize foams in porous media and can be soluble in the aqueous phase, or in the CO2 phase. Aqueous- and CO2-soluble surfactants must be characterized for their ability to reduce CO2 mobility and stabilize foam at reservoir conditions. In addition, numerical models are necessary to predict and evaluate the effect of foam for field-scale applications and require empirical data obtained from core-scale flooding experiments. This study presents a series of steady-state foam co-injections with dense phase CO2 and either aqueous- or CO2-soluble surfactant solutions at varying CO2 flow velocities and CO2 fractions. One anionic water-soluble surfactant, which is considered a benchmark foam stabilizer, and five partially CO2-soluble non-ionic surfactants were investigated. Gamma ray attenuation was used to accurately monitor in-situ saturations during steady-state co-injections. The primary objective was to determine the steady-state foam characteristics of the different surfactants by evaluating the mobility reduction factor (MRF) and the limiting water saturation where foam abruptly collapses (Sw∗). All of the tested surfactants generated foam and reduced CO2 mobility by more than three orders of magnitude. The anionic surfactant increased foam stability at lower water saturations, compared to the non-ionic surfactants, which resulted in lower residual water saturations and increased pore volume available for CO2 storage. Core flooding results provided input into a local-equilibrium foam model. The fitted foam model reproduced the experimental results for the anionic surfactant and for three of the five non-ionic surfactants. The two latter non-ionic surfactants violated model assumptions because non-monotonic water saturation changes were observed, an effect not accurately captured by local-equilibrium foam models. However, the modelling work elucidated subtle experimental trends and demonstrated the applicability of the dataset as input into implicit-texture local-equilibrium foam models.

Experimental Study of Foam Flow in Highly Permeable Porous Media for Soil Remediation

Foam has shown promising characteristics for soil remediation, especially as a blocking agent. In very permeable porous media, high groundwater velocity reduces the efficiency of in situ remediation by decreasing the contact time with contaminants. To use foam to reduce water velocity, this paper investigates its properties in very permeable porous media (> 4.10−10 m2). Alpha olefin sulfonate foam injection experiments were conducted in columns containing glass beads or sand, with varying permeabilities and injection techniques. Pressure and mass balance data were acquired to measure foam resistance factor and liquid saturation. The results show that foam pregeneration is mandatory for generating a highly viscous foam in highly permeable porous media. However, the permeability of the foam generator does not affect the results within the range studied. Pregeneration generated highly viscous foam, even in very high permeable porous media (> 10−9 m2). The influence of permeability on the apparent viscosity of foam in porous media was related to the shear-thinning foam behavior. These experimental results show that foam injection is a relevant method for water blocking and mobility control in highly permeable porous media.