Heterogeneous Micromodel Research Articles

Pore-scale investigation of selective plugging mechanism in immiscible two-phase flow using phase-field method

Biotechnology has had a major effect on improving crude oil displacement to increase petroleum production. The role of biopolymers and bio cells for selective plugging of production zones through biofilm formation has been defined. The ability of microorganisms to improve the volumetric sweep efficiency and increase oil recovery by plugging off high-permeability layers and diverting injection fluid to lower-permeability was studied through experimental tests followed by multiple simulations. The main goal of this research was to examine the selective plugging effect of hydrophobic bacteria cell on secondary oil recovery performance. In the experimental section, water and aqua solution of purified Acinetobacter strain RAG-1 were injected into an oil-saturated heterogeneous micromodel porous media. Pure water injection could expel oil by 41%, while bacterial solution injection resulted in higher oil recovery efficiency; i.e., 59%. In the simulation section, a smaller part of the heterogeneous geometry was employed as a computational domain. A numerical model was developed using coupled Cahn–Hilliard phase-field method and Navier–Stokes equations, solved by a finite element solver. In the non-plugging model, approximately 50% of the matrix oil is recovered through water injection. Seven different models, which have different plugging distributions, were constructed to evaluate the influences of selective plugging mechanism on the flow patterns. Each plugging module represents a physical phenomenon which can resist the displacing phase flow in pores, throats, and walls during Microbial-Enhanced Oil Recovery (MEOR). After plugging of the main diameter route, displacing phase inevitably exit from sidelong routes located on the top and bottom of the matrix. Our results indicate that the number of plugs occurring in the medium could significantly affect the breakthrough time. It was also observed that increasing the number of plugging modules may not necessarily lead to higher ultimate oil recovery. Furthermore, it was shown that adjacent plugs to the inlet caused flow patterns similar to the non-plugging model, and higher oil recovery factor than the models with farther plugs from the inlet. The obtained results illustrated that the fluids distribution at the pore-scale and the ultimate oil recovery are strongly dependent on the plugging distribution.

Lattice Boltzmann simulations of liquid CO2 displacing water in a 2D heterogeneous micromodel at reservoir pressure conditions

We employed the color-fluid lattice Boltzmann multiphase model to simulate liquid CO2 displacing water documented in experiments in a 2D heterogeneous micromodel at reservoir pressure conditions. The main purpose is to investigate whether lattice Boltzmann simulation can reproduce the CO2 invasion patterns observed in these experiments for a range of capillary numbers. Although the viscosity ratio used in the simulation matches the experimental conditions, the viscosity of the fluids in the simulation is higher than that of the actual fluids used in the experiments. Doing so is required to enhance numerical stability, and is a common strategy employed in the literature when using the lattice Boltzmann method to simulate CO2 displacing water. The simulations reproduce qualitatively similar trends of changes in invasion patterns as the capillary number is increased. However, the development of secondary CO2 pathways, a key feature of the invasion patterns in the simulations and experiments, is found to occur at a much higher capillary number in the simulations compared with the experiments. Additional numerical simulations were conducted to investigate the effect of the absolute value of viscosity on the invasion patterns while maintaining the viscosity ratio and capillary number fixed. These results indicate that the use of a high viscosity (which significantly reduces the inertial effect in the simulations) suppresses the development of secondary CO2 pathways, leading to a different fluid distribution compared with corresponding experiments at the same capillary number. Therefore, inertial effects are not negligible in drainage process with liquid CO2 and water despite the low Reynolds number based on the average velocity, as the local velocity can be much higher due to Haines jump events. These higher velocities, coupled with the low viscosity of CO2, further amplifies the inertial effect. Therefore, we conclude that caution should be taken when using proxy fluids that only rely on the capillary number and viscosity ratio in both experiment and simulation.

Micro‐PIV measurements of multiphase flow of water and liquid CO2 in 2‐D heterogeneous porous micromodels

AbstractWe present an experimental study of pore‐scale flow dynamics of liquid CO2 and water in a two‐dimensional heterogeneous porous micromodel, inspired by the structure of a reservoir rock, at reservoir‐relevant conditions (80 bar, 21°C). The entire process of CO2 infiltration into a water‐saturated micromodel was captured using fluorescence microscopy and the micro‐PIV method, which together reveal complex fluid displacement patterns and abrupt changes in velocity. The CO2 front migrated through the resident water in an intermittent manner, forming dendritic structures, termed fingers, in directions along, normal to, and even opposing the bulk pressure gradient. Such characteristics indicate the dominance of capillary fingering through the micromodel. Velocity burst events, termed Haines jumps, were also captured in the heterogeneous micromodel, during which the local Reynolds number was estimated to be ∼21 in the CO2 phase, exceeding the range of validity of Darcy's law. Furthermore, these drainage events were observed to be cooperative (i.e., across multiple pores simultaneously), with the zone of influence of such events extending beyond tens of pores, confirming, in a quantitative manner, that Haines jumps are nonlocal phenomena. After CO2 completely breaks through the porous section, shear‐induced circulations caused by flowing CO2 were also observed, in agreement with previous studies using a homogeneous porous micromodel. To our knowledge, this study is the first quantitative measurement that incorporates both reservoir‐relevant conditions and rock‐inspired heterogeneity, and thus will be useful for pore‐scale model development and validation.

Pore-scale supercritical CO2 dissolution and mass transfer under drainage conditions

Recently, both core- and pore-scale imbibition experiments have shown non-equilibrium dissolution of supercritical CO2 (scCO2) and a prolonged depletion of residual scCO2. In this study, pore-scale scCO2 dissolution and mass transfer under drainage conditions were investigated using a two-dimensional heterogeneous micromodel and a novel fluorescent water dye with a sensitive pH range between 3.7 and 6.5. Drainage experiments were conducted at 9MPa and 40°C by injecting scCO2 into the sandstone-analogue pore network initially saturated by water without dissolved CO2 (dsCO2). During the experiments, time-lapse images of dye intensity, reflecting water pH, were obtained. These images show non-uniform pH in individual pores and pore clusters, with average pH levels gradually decreasing with time. Further analysis on selected pores and pore clusters shows that (1) rate-limited mass transfer prevails with slowly decreasing pH over time when the scCO2-water interface area is low with respect to the volume of water-filled pores and pore clusters, (2) fast scCO2 dissolution and phase equilibrium occurs when scCO2 bubbles invade into water-filled pores, significantly enhancing the area-to-volume ratio, and (3) a transition from rate-limited to diffusion-limited mass transfer occurs in a single pore when a medium area-to-volume ratio is prevalent. The analysis also shows that two fundamental processes – scCO2 dissolution at phase interfaces and diffusion of dsCO2 at the pore scale (10–100µm) observed after scCO2 bubble invasion into water-filled pores without pore throat constraints – are relatively fast. The overall slow dissolution of scCO2 in the millimeter-scale micromodel can be attributed to the small area-to-volume ratios that represent pore-throat configurations and characteristics of phase interfaces. This finding is applicable for the behavior of dissolution at pore, core, and field scales when water-filled pores and pore clusters of varying size are surrounded by scCO2 at narrow pore throats.

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.

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.

Random walk simulation of miscible flow through heterogeneous 2D porous media considering dispersion tensor

Most of numerical approaches describing the behavior of miscible displacement in porous media through the solution of advection–dispersion equation suffer from numerical dispersion. Random Walk (RW) method is a good candidate to overcome this problem especially in heterogeneous media. In addition, how treating dispersion coefficient as a tensor might affect the accuracy of RW simulation results is not well understood. Here, a RW model was developed and used for simulating miscible displacement experiments performed on heterogeneous micromodels including single fracture/flow barrier. Dispersion coefficient was treated as a tensor and a hybrid scheme was used for velocity interpolation. The transient concentration and production data were used for estimation of the diffusion coefficient, longitudinal and transversal dispersivity by fitting the model results to the experimental data. Well match observed between model results and experimental data indicates that RW is an accurate method for simulating miscible displacements by capturing the irregularity of the saturation profiles.

Improvement of Water Flooding Efficiency Using Mixed Culture of Microorganisms in Heterogeneous Micro-models

One of the possible methods for reducing unwanted problem of reservoir heterogeneity in flooding processes is the application of microbial slugs for bioplugging of high permeable zones. Objective of this research is visualization of potential of mixed-culture microorganisms as bioplugging agents for improving the efficiency of water flooding in two different heterogeneous micro-models: a glass bead and an inventive etched one. In both micro-models, water flooding removed the oil in high permeable zones while it had little effect on the oil in low permeable areas. Injection of a slug, containing a mixed culture of oil degrading microorganisms was done in glass bead micro-model. The etched micro-model was used to investigate the effect of in situ microbial growth and subsequent water flooding. In both cases the microbial treatment improved the oil recovery in comparison with water flooding in low permeable zone considerably. The results of this study showed that mixed-culture microorganisms have an acceptable potential for bioplugging of high permeable layers of heterogeneous porous media.

Role of Collector Alternating Charged Patches on Transport of Cryptosporidium parvum Oocysts in a Patchwise Charged Heterogeneous Micromodel

The role of collector surface charge heterogeneity on transport of Cryptosporidium parvum oocyst and carboxylate microsphere in 2-dimensional micromodels was studied. The cylindrical silica collectors within the micromodels were coated with 0, 10, 20, 50, and 100% Fe(2)O(3) patches. The experimental values of average removal efficiencies (η) of the Fe(2)O(3) patches and on the entire collectors were determined. In the presence of significant (>3500 kT) Derjaguin-Landau-Verwey-Overbeek (DLVO) energy barrier between the microspheres and the silica collectors at pH 5.8 and 8.1, η determined for Fe(2)O(3) patches on the heterogeneous collectors were significantly less (p < 0.05, t test) than those obtained for collectors coated entirely with Fe(2)O(3). However, η calculated for Fe(2)O(3) patches for microspheres at pH 4.4 and for oocysts at pH 5.8 and 8.1, where the DLVO energy barrier was relatively small (ca. 200-360 kT), were significantly greater (p < 0.05, t test) than those for the collectors coated entirely with Fe(2)O(3). The dependence of η for Fe(2)O(3) patches on the DLVO energy barrier indicated the importance of periodic favorable and unfavorable electrostatic interactions between colloids and collectors with alternating Fe(2)O(3) and silica patches. Differences between experimentally determined overall η for charged heterogeneous collectors and those predicted by a patchwise geochemical heterogeneous model were observed. These differences can be explained by the model's lack of consideration for the spatial distribution of charge heterogeneity on the collector surface.

Pore-scale investigation of immiscible displacement process in porous media under high-frequency sound waves

Although experimental and theoretical studies have been performed to identify the effects of elastic waves on multi-phase flow in porous structures, the literature lacks finely tuned experiments at the micro-scale. This paper reports observations and critical analysis of immiscible displacement in micro-scale porous media under ultrasonic energy. A number of experiments are performed on homogeneous and heterogeneous micromodels for varying wave frequency and power, initial water saturation, wettability and injection rates. We show that ultrasonic radiation influences the displacement pattern and yields lower residual non-wetting phase (oil) behind when low injection rates are applied. Higher wave frequency results in faster recovery of oil, but the ultimate recovery is controlled mainly by wave intensity. The presence of initial water saturation has a positive effect on the displacement, especially in an oil-wet medium. Of the possible mechanisms suggested for recovery enhancement under ultrasonic radiation, deformation of pore walls and change in fluid properties due to heating are not an issue in these experiments but other mechanisms including coalescence of oil droplets under oscillation, reduction of wetting films, adherence to grains and the peristaltic movement of fluids due to mechanical vibration were observed to be effective and are discussed in the analysis of the visual observations.

Pore-level visual investigation of miscible and immiscible displacements

The mechanisms of oil recovery by gas injection, with particular interest in the generation of highly viscous oil residues and asphaltene flocculation and the resulting permeability impairment, have been studied. The flow visualisation experiments were performed in high pressure heterogeneous micromodels reproduced from real rock micrographs. The visual micromodels were also employed in series with a compatible glass bead pack. Displacement experiments simulating secondary and tertiary recovery of a North Sea crude oil at 27.5 MPa and 33°C were conducted. Methane, propane and water were injected. The displacement video observations and the measurements made are presented. The pore-level investigation of immiscible gas drive revealed the importance of wettability and capillary pressure on the spontaneous movements of the fluid interfaces. Fractions of pores occupied by oil become oil-wet. Thin films of oil on these segments keep the oil phase continuous and results in the flow and recovery of oil trapped in narrow sections of the pores, even at very low capillary numbers. Further observations on oil, gas and connate water movements are also presented. Miscible displacement of oil with propane did not induce any significant precipitation of asphaltenes in pores. However, bulk mixing of propane and oil can promote asphaltenes flocculation, pore plugging and permeability impairment. The deposited materials can be partially dissolved and removed by contacting with fresh oil.