Lamella Division Research Articles

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.

Monitoring of microscopic behavior of nano-enhanced colloidal gas aphron in fractured and un-fractured non-uniform porous medium

The present article aimed to examine the pore-scale examination of a fluid capability to block pores and fractures deduced by return permeability and the blocking ability of a novel lightweight Colloidal Gas Aphron Nano-Fluid (CGANF) in heterogeneous fractured/un-fractured porous medium. Silica (S) and fumed silica (FS) nanoparticles, Sodium Dodecyl Sulfate (SDS) anionic surfactant, and Xanthan Gum (XG) bio-polymer were employed for following up CGANF bubbles' movements in incongruous micro-models’ inclusive crack. The transparent nature of the glass micro-model provides an intuition into the lenticular behavior of CGANF bubbles in the heterogeneous porous media. Differential pressure analysis through porous media during experiments demonstrated that opposition to the stream of CGANF bubbles increased as more CGANF fluid was injected. Also, the lamella division mechanism generated more small bubbles resulting in increasing differential pressure across porous micro-models. Contrasted to bigger CGANF bubbles, smaller CGANF bubbles had lesser movability. Therefore, they were key factors for blocking pores and throats of porous media and changed the orientation of bigger bubbles in cracks toward the matrix. Observations revealed that CGANF micron-bubbles built up through the porous media could set up an impressive snag to control loss of filtrate, and permeability of models was reverted almost to its primary permeability when saturation fluid was reinjected into micro-models. For the detailed analysis in this study, the maximum percentages of reverted permeability for fractured and un-fractured non-uniformed micro-models were attained 91.81% and 90.70%, respectively. Also, by increasing XG concentrations from 0.286 to 0.571% w/v, return permeability percentage increased from 84.4% to 87.4%. There was an optimum concentration of nanoparticles at 0.0571% w/v of silica and fumed silica, and consequently, returned permeability and infusion pressure of CGANF fluid reached their maximum values. Moreover, the stability of the CGANF fluid increased to 8.15% and 12.6% by adding silica and fumed silica nanoparticles, respectively, to the CGA fluid formulation without nanoparticles. This article presents a novel insight into porous media for analyzing blockage capability and controlling porous media damage created via CGANF-based fluids in non-uniformed environments. • Enhancing the behavior and properties of CGANF fluids. • Use of silica and fumed silica nanoparticles in CGANF fluids. • Controlling filtration loss by forming an effective seal using CGA/CGANF fluids. • Use of heterogeneous transparent glass micromodels for monitoring the bubbles flowin the pores and fracture by microscope. • Analysis of return permeability by high accurate pressure drop data through micromodel.

Enhancement of smart water-based foam characteristics by SiO2 nanoparticles for EOR applications

Here, smart water assisted with synthesized SiO2 nanoparticles have been utilized to prepare the foam solution. Effect of SiO2 nanoparticles on foam stability and oil displacement efficiency in carbonated pattern of glass micromodel have been studied. Obtained results showed that foam solution with smart water assisted with silica nanoparticles has the highest stability in comparison to the distilled water and smart water free of nanoparticles. In the presence of the nanoparticles the stability of the foam solution has significantly increased. However, the highest stability of the smart water based-foam solution has been attained with SiO2 nanoparticles at concentration of 3000 ppm. In the foam solution of smart water without the nanoparticles, the values of R5 and half-life (t1/2) are 91.5 and 2813s, respectively. While, these values in the presence of the dispersed nanoparticles reach to about 99.2 and 3812s, respectively. During the injection experiments with foam solution prepared by the smart water mixed with SiO2 nanoparticles in micromodel, the breakthrough of the foam has been postponed and oil recovery factor has been improved. Due to the presence of the silica nanoparticles in foam solution high-thickness lamellae has been formed and snap-off and lamella division phenomena have occurred in porous network on microscopic scale.

Monitoring Polymer-Enhanced Foam Displacements Through Heterogeneous Porous Media: A Pore-Scale Study

AbstractIn this work, fundamental understanding of phase displacements involved in polymer-enhanced air foam is investigated which was not well discussed in the available literature. To do this, a series of foam injection experiments were performed on heterogeneous rock-look-alike micromodels in the presence and absence of a single fracture. The models were initially saturated with crude oil and experienced post polymer-enhanced foam injection process. We observed for the first time the mechanism of synergetic upstream snap-off and lamella division in the vicinity of the area where the permeability contrast was obvious. Observations showed two opposite effects of oil emulsioning and bubble coalescence when gas bubbles came in contact with oil in pore bodies. Fractal dimension analysis of front polymer-enhanced foam illustrates a noticeable improvement in oil displacement. Primary enhanced foam injection to oil saturated micromodel causes bubble coarsening which leads to less efficient oil displacement process. The lower the polymer concentration, the less stable the foam; consequently, the less efficient oil displacement is observed. Lower viscosity oil results in lower recovery efficiency as the stability of foam decreases. To shed light on the dynamic behavior of polymer–surfactant interface, some dynamic surface tension tests were conducted. Results showed that repellency between surfactant and polymer molecules causes surfactant molecules to be present on the surface making the initial dynamic interfacial tension (IFT) decrease. Results of this work help to better understand how polymer could enhance the efficiency of foam floods in heterogeneous systems.

Visualizing pore-scale foam flow in micromodels with different permeabilities

The mechanisms of pore-scale foam transport in porous media help further understanding how foam flows in porous media with different permeabilities. In this work, the pore-scale behaviors of N2 foam flows in porous media with different permeabilities have been investigated using transparent polydimethylsiloxane (PDMS) micromodels with foam qualities in the range of 50 %–90 %. The foam transport in homogeneous and heterogeneous micromodels, and the effects of permeability on foam texture and gas trapping, were evaluated through direct visual observations. Bubble generation based on the pre-existing foam bubbles occurred for trapped and flowing bubbles, which could change the distribution of flowing and trapped gases in the micromodel. Two foam generation mechanisms, namely snap-off and lamella division, were observed in this study. The mean size of bubbles in the low-permeability micromodel was smaller than that in the high-permeability micromodel especially at high foam qualities. The trapped gas saturation in the low-permeability micromodel was larger than that in the high-permeability micromodel. For foam flow in the heterogeneous micromodel, the process of foam diversion from the high-permeability region to the low-permeability region was directly displayed at the pore scale. Regeneration of large trapped bubbles in the low-permeability region under the pressure difference across the micromodel played an important role in this process.

Pore Network Investigation of Trapped Gas and Foam Generation Mechanisms

The mobility of gas is greatly reduced when the injected gas is foamed. The reduction in gas mobility is attributed to the reduction in gas relative permeability and the increase in gas effective viscosity. The reduction in the gas relative permeability is a consequence of the larger amount of gas trapped when foam is present while the increase in gas effective viscosity is explicitly a function of foam texture. Therefore, understanding how foam is generated and subsequent trapped foam behavior is of paramount importance to modeling of gas mobility. In this paper, we push the envelope to enlighten our decisions of which descriptions are most physical to foam flow in porous media regarding both the flowing foam fraction and the rate of generation. We use a statistical pore network interwoven with the invasion percolation with memory algorithm to model foam flow as a drainage process and investigate the dependence of the flowing foam fraction on the pressure gradient and to shed light on foam generation mechanisms. A critical snap-off probability is required for strong foam to emerge in our network. The pressure gradient and, hence, the gas mobility reduction are very low below this critical snap-off probability. Above this snap-off probability threshold, we find that the steady-state flowing lamellae fraction scales as $$(\nabla \tilde{p})^{0.19}$$ in 2D lattices and as $$(\nabla \tilde{p})^{0.32}$$ in 3D lattices. Results obtained from our network were convolved with percolation network scaling ideas to compare the probabilities of snap-off and lamella division mechanisms in the network during the initial gas displacement at the leading edge of the gas front. At this front, during strong foam flow, lamella division is practically nonexistent in 2D lattices. In 3D lattices, lamella division occurs, but the probability of snap-off is always greater than the probability of lamella division.

Foam Generation and Rheology in a Variety of Model Fractures

Gas is used in petroleum reservoirs to displace oil for enhanced oil recovery. The microscopic displacement efficiency of gas is very good, but at the reservoir scale the process suffers from poor sweep efficiency, especially in naturally fractured reservoirs. Foam can improve the sweep. There have been considerable scientific contributions toward understanding foam flow in nonfractured porous media, with relatively little work on foam flow in fractured porous media. We investigate foam-generation mechanisms in five fully characterized glass models of fractures with different apertures and correlation lengths of the aperture distribution. We also study the rheology of the in situ-generated foam by varying the superficial velocities of the gas and surfactant solution. We compare the measured pressure gradient against the fracture attributes, aperture, and the correlation length of the aperture. We also compare foam texture as a function of position within the fracture as the generated foam propagates through the fracture. Gas mobility was greatly reduced as a result of in situ foam generation in our model fractures. Foam was generated predominantly by capillary snap-off and lamella division. The measured mobility reduction depends on fracture attributes. Fracture-wall roughness, represented by both the hydraulic aperture and the correlation length of the aperture, plays an important role in foam generation and mobility. The average bubble size increases as the aperture increases, which results in a significant decrease in pressure gradient. Two model fractures show the same two foam-flow regimes central to the understanding of foam in nonfractured porous media: a low-quality regime where pressure gradient is independent of liquid velocity and a high-quality regime where pressure gradient is independent of gas velocity. The mechanisms thought to be behind these two regimes in nonfractured porous media do not apply to these experiments, however.

Study of foam generation and propagation in fully characterized physical-model fracture

Foam greatly reduces gas mobility for gas enhanced-oil-recovery (EOR) projects. It substantially increases both the effective viscosity of gas and gas trapping. Numerous studies have been conducted to understand foam rheology in rock matrix both theoretically and experimentally. The knowledge of foam flow in fractured porous media is incomplete, however. This study aims to contribute to the understating of foam generation and propagation in a fully characterized physical-model fracture. We investigate foam-generation mechanisms and the propagation of pre-generated foam. Gas mobility was greatly reduced as a result of in-situ foam generation. Foam-generation mechanisms similar to those seen in 3D porous media were observed on this model fracture. Foam was generated predominantly by capillary snap-off and lamella division. Lamella division was observed at high gas fractional flow at two different superficial velocities. Fracture wall roughness played an important role in foam generation. In the case of pre-generated foam, two very distinct bubble sizes were injected: fine-textured bubbles much smaller than the roughness scale and coarse-textured foam with bubbles much larger than the roughness scale. The first case did not show any significant change in bubble size as foam propagated through the model fracture, while in the second case, the fracture played a role in reducing bubble size. Inter-bubble diffusion did not regulate bubble size in our apparatus because residence time in the fracture is relatively short. We cannot confirm that foam reached local equilibrium in our experiments, but we believe that local equilibrium lies between the cases of in-situ- and pre-generated foams.

Lamella Division in a Foam Flowing through a Two-Dimensional Porous Medium: A Model Fragmentation Process

We flow a 2D foam through a model 2D porous medium and study experimentally and numerically how the bubble size distribution evolves along the medium. The dominant mechanism of bubble creation is a fragmentation process occurring when bubbles pinched against obstacles are split in two smaller bubbles. We infer the statistics of these individual and local fragmentation events from the experimental data and propose a fragmentation equation to relate that statistics to the evolution of the global size distribution. The predicted evolution shows very good agreement with direct experimental measurements of the bubble size distribution.

Pore-scale analysis of filtration loss control by Colloidal Gas Aphron Nano-Fluids (CGANF) in heterogeneous porous media

This study concerns micro-scale analysis of filtration loss control induced by blockage ability of a new colloidal gas fluid, Colloidal Gas Aphron Nano-Fluid (CGANF) in fractured porous media. Fumed silica nanoparticles and a novel environmentally friendly bio surfactant, Olea Europaea, were used for monitoring CGANF displacements in heterogeneous micromodels including single fracture. Analysis of pressure drop along the micromodel during tests showed an increasing resistance to flow of CGANF dispersion through porous media as more CGANF was injected. When lamella division occurs, more small bubbles are formed and then pressure drop through porous media increases. Small bubbles play an important role in blocking the porous media due to the fact that they change the direction of larger bubbles in fracture and also due to their lower mobility compared to larger bubbles. Observations revealed that CGANF microbubble built up across the pore structure could establish an effective seal for controlling filtration loss. The permeability of the porous media can be returned to the original state. For the cases studied here, the highest value of return permeability for fractured and un-fractured heterogeneous patterns were 71.11% and 78%, respectively. Nanoparticles improved the blockage ability of CGANF injection at 0.1w/v% concentration as an optimum concentration. This study provides new insights into the pore blocking ability and formation damage control induced by CGANF in heterogeneous systems.

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.

Experimental Study on Stability and Improving Sweep Efficiency with Microfoam in Heterogeneous Porous Media

In this paper, we attempted to prepare microfoam by using a sandpack filled with glass beads with co-flowing gas and foaming solution, the microfoam stability and effectiveness in improving profile control capacity at micromodel and pore media were evaluated by micromodel tests and double-core experiments. The results of micromodel tests showed that microfoam stability was increased with increasing xanthan gum concentration due to a higher solution viscosity and viscoelasticity of liquid film. The xanthan gum-stabilized microfoam had a longer propagation distance through the low permeable region of heterogeneous micromodel at time of breakthrough than common microfoam, the optimum performance of microfoam for fluid diversion was multiple bubble trapping and mobilization rather than lamella division. According to the results of double-core experiments, the microfoam could plug the high permeability sandpack and improve the sweep efficiency in the low permeability sandpack, which could improve the water injection profile of porous media effectively. The increase in profile control effects had a good correspondence with the increase of xanthan gum concentration. The presented results were useful in understanding and designing microfoam injection in reservoirs for enhanced oil recovery.

Simulations of bubble division in the flow of a foam past an obstacle in a narrow channel

When foams flow through porous media, the interaction of the lamellae with the walls of the channels leads to changes in the bubble size distribution. We predict these changes using Surface Evolver simulations of simple foam structures subject to bubble creation via lamella division. We use a model porous medium consisting of a disc in a straight channel. The position of the disc within the channel is shown to significantly affect the final polydispersity of the foam, with a slightly off-centre disc giving the highest polydispersity. We also find that after repeated passes of the foam through the channel, the process of bubble division eventually ceases, leaving a foam with an average bubble area slightly larger than the disc size.

Improved mechanistic foam simulation with foam catastrophe theory

Abstract Recent experimental studies discovered that foam exhibits three different states (weak-foam, intermediate, and strong-foam states) reminiscent of catastrophe theory, and the strong-foam state consists of two distinct flow regimes (high-quality and low-quality regimes). No existing foam simulators can handle these concepts properly, especially when the simulation comes to near the limiting capillary pressure, P c * (or the limiting water saturation, S w * , equivalently) at which foam breaks down abruptly. Capturing the delicate feedback mechanism near P c * has been a great challenge in mechanistic foam simulations. This study presents how to build a mechanistic foam simulator consistent with foam catastrophe theory and two steady-state strong-foam regimes. More importantly, this study for the first time resolves the issues on the instability and divergence of numerical simulation that take place near the physical discontinuity (i.e., P c * or S w * ) in foam simulation. Results showed that it was necessary to choose an appropriate lamella-creation function to ensure the stability and convergence. Specifically (1) the lamella-creation function should increase rapidly above a certain pressure gradient (▿P), known as a minimum pressure gradient (▿Pmin) for lamella mobilization and division, to kick off active bubble generation, and (2) the function should also reach a plateau at high ▿P at which foam rheology is governed by bubble coalescence rather than bubble generation. This new mechanistic simulator required five parameters to fit the steady-state foam catastrophe, the two flow regimes, and dynamic foam coreflood data, each of which was determined uniquely. The foam model in this study manifested that active (or, inactive) lamella-creation mechanism could be compensated by active (or, inactive) lamella-coalescence mechanism in the modeling process. The level of how active these mechanisms were, however, had a significant impact on the shift from weak-foam to strong-foam propagation during dynamic foam displacement. Simulations were extended not only to simultaneous injection of gas and surfactant solutions in a wide range of injection velocities, but also to alternating gas and surfactant solutions in which the dynamic mechanisms near P c * is the key to field performance. Results were compared and verified with fractional flow analysis that was equipped with mechanistic foam mechanisms.

Pore-network study of the mechanisms of foam generation in porous media

Understanding the role of pore-level mechanisms is essential to the mechanistic modeling and simulation of foam processes in porous media. Three different pore-level events can lead to foam formation: snapoff, leave behind, and lamella division. The initial state of the porous medium (fully saturated with liquid or already partially drained), as surfactant is introduced, also affects the different foam-generation mechanisms. Bubbles created by any of these mechanisms cause the formation of new bubbles by snapoff and leave behind as gas drains liquid-saturated pores. Lamellae are stranded unless the pressure gradient is sufficient to mobilize those that have been created. To appreciate the roles of these mechanisms, their interaction at the pore-network level was studied. We report an extensive pore-network study that incorporates the above pore-level mechanisms, as foam is created by drainage or by the continuous injection of gas and liquid in porous media. Pore networks with up to 10 000 pores are considered. The study explores the roles of the pore-level events, and by implication, the appropriate form of the foam-generation function for mechanistic foam simulation. Results are compared with previous studies. In particular, the network simulations reconcile an apparent contradiction in the foam-generation model of Rossen and Gauglitz [AIChE J. 36, 1176 (1990)], and identify how foam is created near the inlet of the porous medium when lamella division controls foam generation. In the process, we also identify a new mechanism of snap-off and foam generation near the inlet of the medium.

Insights on foam generation in porous media from pore-network studies

We report an extensive pore-network study that incorporates pore-level mechanisms, as foam is created by drainage or the continuous injection of gas and liquid in porous media. Pore networks with up to 10,000 pores are considered, with rules for the formation and movement of foam lamellae by the mechanisms of snap-off, leave-behind and lamella division enforced throughout. The study explores the roles of these mechanisms, and by implication, the appropriate form of the foam-generation function for mechanistic foam simulation. Results are compared with previous studies. In particular, they reconcile an apparent contradiction in the foam-generation model of Rossen and Gauglitz [W.R. Rossen, P.A. Gauglitz, Percolation theory of creation and mobilization of foam in porous media, AIChE J. 36 (1990) 1176], and identify how foam is created near the inlet of the porous medium when lamella division controls foam generation. In the process, we identify a new mechanism of snap-off and foam generation near the inlet of the medium.

Percolation modeling of foam generation in Porous media

A foam is a dispersion of a large volume of gas in a continuous liquid phase, stabilized by surfactant. Foams can improve sweep efficiency and oil recovery in gas-injection enhanced oil recovery projects. An important issue for these foam processes is the ease of foam generation in porous media. Previously, Rossen and Gauglitz (1990) derived a percolation model for foam generation in steady gas-liquid flow in porous media. More recent advances in percolation theory require modification of this model, as described in this note. Briefly, Rossen and Gauglitz assumed that the liquid films or lamellae present in foam block a randomly selected fraction (1 [minus] f) of the pore throats in the medium. Creating the large number of lamellae that define a foam from the relatively few present initially requires displacing these lamellae from their pore throats so they can multiply by the processes of lamella division and repeated snapoff. Displacing lamellae from pore throats to initiate the generation process requires imposing a pressure difference across the throat of order one or a few kPa (a few tenths of a psi). Generating'' foam, therefore, depends on lamella mobilization, which depends on the magnitude of the pressure drop [Delta]P across individualmore » pore throats blocked by lamellae. Rossen and Gauglitz's model predicts that the minimum pressure gradient for foam generation [del]P[sup min] decreases nearly linearly, as f approaches f[sub c], the percolation threshold for the pore network, from either direction.« less

Mechanisms of Foam Generation in Glass-Bead Packs

SummaryThe fundamental, pore-level mechanisms of foam generation are investigated in monodisperse bead packs. First, direct visual observations identify the following generation mechanisms: lamella leave-behind, gas-bubble snap-off, and lamella division. Then, to ascertain the relative importance of these mechanisms, quantitative experiments are pursued on the role of bead- pack permeability (bead sizes from 0.25 to 1 mm [0.01 to 0.04 in.]), gas-phase velocity (0.001 to 0.8 cm/s [0.0004 to 0.3 in./sec]), gas-phase fractional flow (0.60 to 1.0), permeability variations, and surfactant type [sodium dodecyl benzene sulfonate (SDBS), sodium dodecyl sulfate (SDS), Chevron Chaser SD1000™, and Suntech IV 1035™]. We discover a critical velocity, above which a "strong" foam is generated and below which only "weak" foam is formed. The snap-off mechanism is the primary mechanism responsible for the formation of the strong foam. A simple model, based on the concept of a "germination site," is developed to predict the onset of snap-off at higher gas velocities. New experimental data obtained in the homogeneous glass-bead packs for the critical capillary number necessary to form a strong foam are in excellent agreement with the proposed germination- site model.