Immiscible Displacement Processes Research Articles

Estimation of Capillary‐Associated NAPL‐Water Interfacial Areas for Unconsolidated Porous Media by Kinetic Interface Sensitive (KIS) Tracer Method

AbstractBy employing kinetic interface sensitive (KIS) tracers, we investigate three different types of glass‐bead materials and three natural porous media systems to quantitatively characterize the influence of the porous‐medium grain‐, pore‐size and texture on the specific capillary‐associated interfacial area (FIFA) between an organic liquid and water. By interpreting the breakthrough curves (BTCs) of the reaction product of the KIS tracer hydrolysis, we obtain a relation for the specific IFA and wetting phase saturation. The immiscible displacement process coupled with the reactive tracer transport across the fluid–fluid interface is simulated with a Darcy‐scale numerical model. Linear relations between the specific capillary‐associated FIFA and the inverse mean grain diameter can be established for measurements with glass beads and natural soils. We find that the grain size has minimal effect on the capillary‐associated FIFA for unconsolidated porous media formed by glass beads. Conversely, for unconsolidated porous media formed by natural soils, the capillary‐associated FIFA linearly increases with the inverse mean grain diameter, and it is much larger than that from glass beads. This indicates that the surface roughness and the irregular shape of the grains can cause the capillary‐associated FIFA to increase. The results are also compared with the data collected from literature, measured with high resolution microtomography and partitioning tracer methods. Our study considerably expands the applicability range of the KIS tracers and enhances the confidence in the robustness of the method.

Modeling Microscale Foam Propagation in a Heterogeneous Grain-Based Pore Network with the Pore-Filling Event Network Method

Foam flooding is an efficient and promising technology of enhanced oil recovery that significantly improves sweep efficiency of immiscible displacement processes by providing favorable mobility control on displacing fluids. Although the advantages in flexibility and efficiency are apparent, accurate prediction and effective control of foam flooding in field applications are still difficult to achieve due to the complexity in multiphase interactions. Also, conventional field-scale or mesoscale foam models are inadequate to simulate recent experimental findings in feasibility of foam injection in tight reservoirs. Microscale modeling of foam behavior has been applied to further connect those pore-scale interactions and mesoscale multiphase properties such as foam texture and the relative permeability of foam banks. Modification on a microscale foam model based on a pore-filling event network method is proposed to simulate its propagation in grain-based pore networks with varying degrees of heterogeneity. The impacts of foam injection strategy and oil-weakening phenomena are successfully incorporated. Corresponding microfluidic experiments are performed to validate the simulation results in dynamic displacement pattern as well as interfacial configuration. The proposed modeling method of foam propagation in grain-based networks successfully captures the effects of lamellae configurations corresponding to various foaming processes. The results of the simulation suggest that the wettability of rock has an impact on the relevance between reservoir heterogeneity and the formation of immobile foam banks, which supports the core idea of the recently proposed foam injection strategy in tight oil reservoirs with severe heterogeneity, that of focusing more on the IFT adjustment ability of foam, instead of arbitrarily pursuing high-quality strong foam restricted by permeability constraints.

Impact of wettability on immiscible displacement in water saturated thin porous media

The characterization of immiscible displacement processes at the pore scale is crucial in order to understand macroscopic behaviors of fluids for efficient use of multiphase transport in various applications. In this study, the impact of porous material wetting properties on gas invasion behavior at various gas injection rates was investigated for thin hydrophilic porous media. An experimentally validated two-phase computational fluid dynamics model was employed to simulate the dynamic fluid–fluid displacement process of oxygen gas injection into liquid water saturated thin porous media. A phase diagram was developed through a parametric characterization of the thin porous media in terms of the material hydrophobicity and gas flow rates. In addition to calculating the saturation of the invading gas, gas pressure variations were calculated and used to identify the locations of phase diagram boundaries. Non-wetting phase streamlines resolved at the microscale were visualized and presented as a novel indicator for identifying displacement regimes and phase diagram boundaries. It was observed that the crossover from the capillary fingering regime to the stable displacement regime occurred between contact angles of 60° and 80°. By increasing the gas injection rate, due to viscous instabilities, flow patterns transitioned from the capillary fingering and stable displacement regimes to viscous fingering regime.

Wettability impacts residual trapping of immiscible fluids during cyclic injection

Understanding the hysteretic behaviour in fluid–fluid displacement processes in porous media is critical in many engineering applications. In this work, we study the quasi-static immiscible displacement process in two-dimensional porous media during cyclic injections in the context of carbon geosequestration. The role of wettability on the residual trapping of CO $_2$ is investigated numerically using an extended interface tracking algorithm. Despite that higher CO $_2$ saturation can be achieved in CO $_2$ -wet porous media after the first CO $_2$ injection, the majority of CO $_2$ is found to be unstable and can be mobilised during subsequent water injection processes. An improvement in the residual trapping of CO $_2$ is observed as the number of injection cycles increases, which is associated with the dispersion of continuous CO $_2$ ganglia into numerous smaller blobs. Compared with either water-wet or CO $_2$ -wet porous media, it is found that less CO $_2$ is trapped within the neutral-wet ones at equilibrium state after a sufficient number of injection cycles. The hysteretic behaviour of saturation between water/CO $_2$ injection cycles is found to follow an exponential decay, which eventually reaches a finite value. This process corresponds to the shift of the mobile region during displacement from typical capillary fingering to a less ramified regime, which ultimately converges towards main flow channels. This work highlights the hysteretic behaviour during cyclic injections, providing insights on the wettability impacts on multiphase flow in porous media, which is of great importance in applications such as carbon geosequestration and geological hydrogen storage.

Linear instability of interfacial Hele-Shaw flows of viscoelastic fluids

We present a theoretical study on the role of elasticity in causing fingering or fracturing instability during the immiscible displacement process of a viscoelastic fluid by another viscoelastic fluid in a rectilinear Hele-Shaw cell. Upper convected Maxwell (UCM) models are used for both fluid layers and linear stability analysis is performed in the regime of moderate to large Deborah number. This is a generalization of Hai and Daripa (2022) where the case of a Newtonian fluid displacing an UCM fluid is considered. The elastic effect of the displacing layer has a significant impact on the overall flow stability. The dispersion relation is implicitly given by a quartic polynomial equation with coefficients depending on a modified wavenumber k ˆ , viscosity contrast η r / η l (displaced/displacing fluid), relaxation time contrast λ r / λ l and a composite parameter β inversely proportional to the flow speed U (depth averaged). Viscous effect is still the dominant mechanism in determining long wave stability (unstable if η r / η l > 1 ). The elastic effect of the displacing layer always destabilizes short waves (unstable if wavelength is shorter than λ l U ). In addition, three types of singular behaviors are found all of which are associated with elastic effects: (i) velocity becomes singular at infinitely many isolated wavenumbers (precise values are inversely proportional to λ l U or λ r U ); (ii) stress becomes singular if wavenumber exceeds certain value (can happen even for slow flow); and (iii) growth rate becomes singular at up to two wavenumbers if η r / η l , λ r / λ l and β fall within a certain range but this can always be avoided if flow is slow enough. The special cases of an UCM fluid displacing air or a viscous Newtonian fluid are also considered. • Analytic solutions for perturbations. • Explicit formulas for the dispersion relations. • Viscous effect dominates long wave stability. • The elastic effect of the displacing fluid destabilizes short waves. • Singularities associated with elasticity in connection with fracturing instability.

Experimental and Analytical Investigation of an Immiscible Displacement Process in Real Structure Micromodels

The recovery of oil from a reservoir can be accomplished with various methods, one of the most commonly applied types being waterflooding. A common theory used to describe immiscible displacement is the Buckley–Leverett theory. A brand new type of micromodel, generated and fabricated by using a micro-computer tomography (μCT) image stack of a real sandstone core, was used to conduct immiscible displacement experiments. Critical logging data were recorded, and a high-resolution camera took pictures of the displacement process. In an image processing tool (MATLAB), an algorithm was developed to evaluate the pictures of the experiment and to examine the changes in the saturations of the displacing and the displaced fluid. The main objective of the displacement experiment was to validate the new microchip in two-phase displacement experiments and to assess the feasibility of the image processing algorithm. This was performed by comparing the results of the experimental to the analytical solutions, which were derived from the Buckley–Leverett theory. The comparison of the results showed a good match between the two types of solutions. The applicability of the analytical results to the experimental procedures was observed. Additionally, the usage of the newly fabricated micromodel and its potential to visualize the fluid flow behavior in porous media were assessed.

A review of fluid displacement mechanisms in surfactant-based chemical enhanced oil recovery processes: Analyses of key influencing factors

Surfactant-based oil recovery processes are employed to lower the interfacial tension in immiscible displacement processes, change the wettability of rock to a more water-wet system and emulsify the oil to displace it in subsurface porous media. Furthermore, these phenomena can reduce the capillary pressure and enhance spontaneous imbibition. The key factors affecting such immiscible displacement process are temperature, salinity and pH of the fluids, surfactant concentration and adsorption. Therefore, before any surfactant flooding process is applied, extensive studies of fluid-fluid and rock-fluid interactions are needed. The use of other chemicals along with surfactants in chemical enhanced oil recovery (cEOR) processes have been widely considered to exploit the synergy of individual chemicals and complement the weakness arises from each of them during immiscible displacement of fluids in porous media. Therefore, such combinations of chemicals lead to alkaline-surfactant (AS), surfactant-polymer (SP), alkaline-surfactant-polymer (ASP), and nanoparticle-surfactant (NS) flooding processes, among others. In this review study, we categorised the role and displacement mechanisms of surfactants and discussed the key factors to be considered for analysing the fluid displacement in porous media.

The Impact of Wettability on Dynamic Fluid Connectivity and Flow Transport Kinetics in Porous Media.

Usually, models describing flow and transport for sub‐surface engineering processes at the Darcy‐scale do not take into consideration the effects of pore‐scale flow regimes and fluid connectivity on average flow functions. In this article, we investigate the impact of wettability on pore‐scale flow regimes. We show that fluid connectivity at the pore scale has a significant impact on average flow kinetics and therefore its contribution should not be ignored. Immiscible two‐phase flow simulations were performed in a two‐dimensional model of a Berea sandstone rock for wettability conditions ranging from moderately water‐wet to strongly oil‐wet. The simulation results show that wettability has a strong impact on invading fluid phase connectivity, which subsequently influences flow transport resistance. The effect of invading‐phase connectivity and ganglion dynamics (GD) on two‐phase displacement kinetics was also investigated. It was found that invading phase connectivity decreases away from the neutrally wet (intermediate wet) state. This study provides evidence that GD accelerate fluid flow transport kinetics during immiscible displacement processes. Lastly, the impact of wettability on fluid displacement efficiency and residual saturations was investigated. Maximum displacement efficiency occurred at the neutrally wet state.

Role of heterogeneous surface wettability on dynamic immiscible displacement, capillary pressure, and relative permeability in a CO2-water-rock system

Surface wettability is one of the major factors that regulate immiscible fluid displacement in porous media. However, the role of pore-scale wettability heterogeneity on dynamic immiscible displacement is rarely investigated. This study investigated the impact of pore-scale wettability heterogeneity on immiscible two-fluid displacement and the resulting macroscopic constitutive relations, including the capillary pressure-water saturation (Pc-Sw) and relative permeability curves. A digital Bentheimer sandstone model was obtained from X-ray micro-computed tomography (micro-CT) scanning and the rock surface wettability fields were generated based on in-situ measurements of contact angles. A graphics processing unit-accelerated lattice Boltzmann model was employed to simulate the immiscible displacement processes through the primary drainage, imbibition, and second drainage stages in a CO2-water-rock system. We found that pore-scale surface wettability heterogeneity caused noticeable local supercritical CO2 (scCO2) and water redistribution under less water-wet conditions. At the continuum scale, the Pc-Sw curves under the heterogeneous wetting condition were overall similar to those under the homogeneous wetting condition. This is because the impact of local wettability heterogeneity on the large-scale Pc-Sw curve was statistically averaged out at the entire-sample scale. The only difference was that heterogeneous wettability led to a negative entry pressure at the primary drainage stage under the intermediate-wet condition, which was caused by local, scCO2-wet surfaces. The impact of pore-scale wettability heterogeneity was more noticeable on the relative permeability curves. Particularly, the variation of the scCO2 relative permeability curve in the heterogeneous wettability scenario was more significant than that in the homogenous wettability scenario. This suggests that pore-scale wettability heterogeneity enhances the coalescence and snap-off behaviors of scCO2 blobs. This is the first study that systematically investigated the role of pore-scale wettability heterogeneity on dynamic immiscible displacement and associated Pc-Sw curves in complicated, three-dimensional porous media.

Viability assessment of integrated P- and S-wave surveys using ultrasound

Potential of, integrated geophysical, especially P- and S-wave combined near surface surveys, is assessed; demonstrated with use of sparingly, reduced chronographic i. e., time and velocity, (1 MHz) ultrasonic imaged data. Case of aqueous and non-aqueous, predominantly, fossil fuel origins spills seepage within near-surface geology is examined in terms of evaluation of possible complexities of fluids and surrounding interactions; which are experimentally simulated embodied as flow components of an immiscible displacement process. Such processes are understood and studied widely, within various, especially near-field geo- and engineering including environmental and also geo-disaster contexts. Interesting relevant scenarios, including aspects, of geological complexity of well known geographical locations while their subjugation also to various, whether natural or anthropogenic, stressors are presented alongside pertinent theory for better grasp, including plausibility, of methodology and inferring. Experimental analogues and geometrical constraints are explained in detail. Ultrasonic P- and S-wave, data in relevant context, also verified analytically, are comprehensively evaluated. S-wave data not only corroborates P-wave data attributes in time-space localization of displaced, from displacing phase, including a “dim spot”, an interesting artifact corresponding to interface (or mixed phase) region, S-wave also manifested other elastic and thermo-mechanical characteristics of the same feature. Further a flow rate, especially, that of injection, control or dependence of a planned displacement process was confirmed, for example if required in tracer and remedial studies. S-waves characteristic suitability to reveal other fluid-fluid and fluid-solid interaction peculiarities at micro and possibly at nano scale, as amplitude effects, is foreseen to assume significant promise.

Pore-scale investigation of immiscible fluid displacement process in randomly distributed bead-based porous micromodels using Micro-PIV

This study reports pore-scale immiscible displacement processes in a bead-based porous micromodel using fluorescence microscopy and micro-particle image velocimetry (μ-PIV) technique. The porous micromodels with heterogeneous and homogeneous geometry are fabricated to investigate the effect of displacing phase viscosity and flow rate on the pore-scale displacement mechanism. The phenomena of shear-induced circulations and viscous instability are observed during the displacement of the trapped non-wetting phase through the porous domain. Breakage and coalescence of the droplets of the non-wetting phase were also observed during the displacement process. The velocity vector maps show that there is frequent flow reversal of ganglia, leading to an unsteady flow behaviour during the displacement process. The effect of flow rate and viscosity on the trapped non-wetting phase is investigated, and the results obtained indicate that an increase in the flow rate reduces the trapped non-wetting fluid saturation in the porous medium by disintegrating large ganglia into small droplets. Increasing either the flow rate or viscosity increases the shear stress at the interface of the trapped ganglion and displacing phase, leading to shear-induced circulations, and the strength of the vortex is found to increase. These circulations inhibit further displacement of the trapped fluids. At higher flow rate with more viscous displacing phase, the trapped non-wetting phase ganglion disintegrate into smaller droplets. It is observed that a heterogeneous micromodel causes significant trapping and lesser mobilization of the non-wetting phase compared to a homogeneous system. The porous medium with low porosity and a higher degree of heterogeneity results in more trapping and less recovery of the non-wetting phase.

An investigation of viscous oil displacement in a fractured porous medium using polymer-enhanced surfactant alternating foam flooding

Naturally fractured reservoirs are one of the hydrocarbon resources where the application of foam flooding is particularly recommended, as foam can divert the flow of displacing fluid from high-permeability regions (fracture networks) to low-permeability regions (rock matrix blocks). However, its application in heavy oil reservoirs is challenging and results in inadequate sweep efficiencies. The current practice of foam flooding (including polymer enhanced foam flooding, PEF) is inefficient in displacing high viscosity oils. This is due to large viscous forces associated with the oil phase flow and the high rate of bubbles coalescence (foam collapse), which make it difficult for foam to displace the heavy oil from the matrix. Thus, we investigated feasibility of polymer-enhanced surfactant alternating foam (PESAF) flooding (as a new hybrid enhanced oil recovery process) to displace the oil phase in porous media. We hypothesized that PESAF flooding can emulsify the oil phase and generate oil globules by reducing the interfacial tension forces between the oil and water phase, and also it increases the foam stability, leading to higher displacement efficiencies in the presence of viscous oils. For this purpose, three different oils (low, medium, and high viscosity oils) were used in a micromodel to simulate the immiscible displacement process in fractured rocks. The experimental results showed that PEF flooding is efficient in displacing the low viscosity oil, however it cannot yield a high efficiency displacement in viscous oil cases. It was found that the hybrid enhanced oil recovery (EOR) process of PESAF flooding can increase the oil recovery factors for the medium and high viscosity oil cases significantly. These experimental results supported the hypothesis of applying PESAF flooding to improve the displacement efficiency of high viscosity oils in fractured porous media.

Control of Generalized Capillary Number on Immiscible Displacement Path: NMR Online and Network Simulation of Fluid Displacement Mechanism

Tight sandstone has a complex pore-throat structure and usually has multiple immiscible displacement paths. Capillary number may control and affect this process, but its control mechanism is still unclear. Therefore, this work aims to study the control process of generalized capillary number on the immiscible displacement process of tight sandstone. Through nuclear magnetic resonance (NMR) online experiments, real-time monitoring of changes in remaining oil in different-radius pores was performed under the control of different generalized capillary numbers. Combined with the microscopic experimental results of a scanning electron microscope and thin-section and constant-speed mercury intrusion, the pore-throat distribution law was obtained, and a pore network model based on a real core was established. The results show that under the control of low capillary numbers, the immiscible displacement path shifts to large and medium pores, while under the control of medium and high capillary numbers, the displacement path shifts to medium and small pores. Moreover, the simulation results also showed interesting phenomena that were not realized in the experiment. When the number of capillaries increases to a certain value (Ca ≈ 6.734 × 10–2 in this study area), unfavorable viscous displacement will occur in tight sandstones, that is, the displacement efficiency will decrease rapidly.

Pore-scale effects during the transition from capillary- to viscosity-dominated flow dynamics within microfluidic porous-like domains

We perform a numerical and experimental study of immiscible two-phase flows within predominantly 2D transparent PDMS microfluidic domains with disordered pillar-like obstacles, that effectively serve as artificial porous structures. Using a high sensitivity pressure sensor at the flow inlet, we capture experimentally the pressure dynamics under fixed flow rate conditions as the fluid–fluid interface advances within the porous domain, while also monitoring the corresponding phase distribution patterns using optical microscopy. Our experimental study covers 4 orders of magnitude with respect to the injection flow rate and highlights the characteristics of immiscible displacement processes during the transition from the capillarity-controlled interface displacement regime at lower flow rates, where the pores are invaded sequentially in the form of Haines jumps, to the viscosity-dominated regime, where multiple pores are invaded simultaneously. In the capillary regime, we recover a clear correlation between the recorded inlet pressure and the pore-throat diameter invaded by the interface that follows the Young–Laplace equation, while during the transition to the viscous regime such a correlation is no longer evident due to multiple pore-throats being invaded simultaneously (but also due to significant viscous pressure drop along the inlet and outlet channels, that effectively mask capillary effects). The performed experimental study serves for the validation of a robust Level-Set model capable of explicitly tracking interfacial dynamics at sub-pore scale resolutions under identical flow conditions. The numerical model is validated against both well-established theoretical flow models, that account for the effects of viscous and capillary forces on interfacial dynamics, and the experimental results obtained using the developed microfluidic setup over a wide range of capillary numbers. Our results show that the proposed numerical model recovers very well the experimentally observed flow dynamics in terms of phase distribution patterns and inlet pressures, but also the effects of viscous flow on the apparent (i.e. dynamic) contact angles in the vicinity of the pore walls. For the first time in the literature, this work clearly shows that the proposed numerical approach has an undoubtable strong potential to simulate multiphase flow in porous domains over a wide range of Capillary numbers.

Simultaneous Occurrence of Miscible and Immiscible Displacement Processes During Solvent Displacement of Heavy Oil: A Parametric Analysis Using Visual Capillary-Tube Experiments

Summary Oil/solvent mixing is essential during solvent-injection applications to reduce the viscosity of oil, but mass transfer by diffusion becomes slower because the oil becomes heavier. Thus, an interface exists between the oil and solvent at certain times, being stronger in the beginning of the process. This results in an immiscible displacement controlled by the capillary forces while mixing is in progress. It is of practical and fundamental importance to determine the mechanisms responsible for the displacement of heavy oil and the behavior of solvents (acting as both immiscible and miscible displacement agents) because it could be advantageous to accelerate the dilution of heavy oil in many circumstances, including heterogeneous (fractured, layered, wormholed) systems. This is a complex process consisting of multiple pore phases (oil, solvent, their mixtures, and aqueous and vapor phases) at the same time, while different mechanisms such as capillary imbibition, miscible interaction (diffusion and convection), and gravity also act simultaneously. To investigate this complex phenomenon for different oil/solvent systems, a novel experimental method was used. The underlying mechanisms that dominate the solvent displacement process were comprehensively identified. The movement and evolution of interfaces among different fluid phases in glass capillary tubes were observed and recorded. Oil samples with different viscosities were used to examine the effects of oil viscosity on the mass transfer accelerated by imbibition transfer. The effects of temperature, wettability, and boundary conditions on the interaction of miscible fluid pairs were also studied. Pentane, heptane, and decane were used as the solvent phases. Advanced photographic techniques using ultraviolet (UV) light and dyed fluids were applied to better track the flow of different phases in the mixing zone. The experiments demonstrated a slowly smearing interface between the solvent and viscous oil. A unique natural convection was induced, with the combined effect of gravity, diffusion (mixing), and capillarity all contributing to the recovery of heavy oil. On the basis of the saturation method, boundary condition, and the Bond number, four different motion modes of mixing zone and interfaces of miscible fluids in the capillary tube were revealed and categorized to identify the degree of interface development (immiscible flooding). Also, the mixing zone, mass flux, and flow behavior were quantified using dimensionless parameters. The results indicate that priority may be given to a solvent with a high interfacial tension (IFT) for the solvent-based oil-recovery technique because of a strong imbibition and further enhancement of the dilution and displacement processes under conditions of a similar viscosity ratio. The data provided will be useful for the accuracy of modeling studies, especially for complex geologies where oil/solvent interaction is critically difficult to develop in order for mixing to occur.

Pore scale investigation on scaling-up micro-macro capillary number and wettability on trapping and mobilization of residual fluid

The mobilization mechanism of the trapped phases controlled by the viscous force and capillary force in porous media is crucial to various engineering applications. In this paper, pore scale water flooding process in rock models with nonuniform wettability is simulated by computational fluid dynamics (CFD) using the volume of fluid (VOF) model. Four types of rock are imaged by micro-CT (μ-CT) and adopted as inputs to generate the structured mesh models. The simulations of two-phase flow are carried out to study the immiscible displacement process in the development of oil fields. The scaling-up critical capillary number at micro-macro scale are acquired and validated, the effects of which on relative permeability, residual oil recovery and immiscible displacement efficiency are analyzed. The simulation results indicate that the critical capillary number at microscopic scale ranges from 10−6 to 10−5 for water-wetted and oil-wetted rock respectively, and approaches to 1 at the macro scale. The effect of wettability on oil recovery is positive for intermediate-wetted or weak water-wetted rock, while negative for strong wettability.

Lattice Boltzmann simulation of immiscible displacement in the cavity with different channel configurations

In this work, the immiscible displacement in a cavity with different channel configurations is studied using an improved pseudo-potential lattice Boltzmann equation (LBE) model. This model overcomes the drawback of the dependence of the fluid properties on the grid size, which exists in the original pseudo-potential LBE model. The approach is first validated by the Laplace law. Then, it is employed to study the immiscible displacement process. The influences of different factors, such as the surface wettability, the distance between the gas cavity and liquid cavity and the surface roughness of the channel are investigated. Numerical results show that the displacement efficiency increases and the displacement time decreases with the increase of the surface contact angle. On the other hand, the displacement efficiency increases with increasing distance between the gas cavity and the liquid cavity at first and finally reaches a constant value. As for the surface roughness, two structures (a semicircular cavity and a semicircular bulge) are studied. The comprehensive results show that although the displacement processes for both the structures depend on the surface wettability, they present quite different behaviors. Specially, for the roughness structure constituted by the semicircular cavity, the displacement efficiency decreases and displacement time increases evidently with the size of the semicircular cavity for the small contact angle. The trend slows down as the increase of the contact angle. Once the contact angle exceeds a certain value, the size of the semicircular cavity almost has no influence on the displacement process. While for the roughness structure of a semicircular bulge, the displacement efficiency increases with the size of bulge first and then it decreases for the small contact angle. The displacement efficiency increases first and finally reaches a constant for the large contact angle. The results also show that the displacement time has an extreme value in these cases for the small contact angles.

Toward Reservoir-on-a-Chip: Fabricating Reservoir Micromodels by in Situ Growing Calcium Carbonate Nanocrystals in Microfluidic Channels.

We introduce a novel and simple method to fabricate calcium carbonate (CaCO3) micromodels by in situ growing a thin layer of CaCO3 nanocrystals with a thickness of 1-2 μm in microfluidic channels. This approach enables us to fabricate synthetic CaCO3 reservoir micromodels having surfaces fully covered with calcite, while the dimensions and geometries of the micromodels are controllable on the basis of the original microfluidic channels. We have tuned the wettability of the CaCO3-coated microchannels at simulated oil reservoir conditions without introducing any chemical additives to the system; thus the resulting oil-wet surface makes the micromodel more faithfully resemble a natural carbonate reservoir rock. With the advantage of its excellent optical transparency, the micromodel allows us to directly visualize the complex multiphase flows and geochemical fluid-calcite interactions by spectroscopic and microscopic imaging techniques. The CaCO3-coated microfluidic channels provide new capabilities as a micromodel system to mimic real carbonate reservoir properties, which would allow us to perform a water-oil displacement experiment in small-volume samples for the rapid screening of candidate fluids for enhanced oil recovery (EOR). The immiscible fluid displacement process within carbonate micromodels has been demonstrated showing the water-oil-carbonate interactions at pore-scale in real time by fluorescence microscopic imaging.

Operator-based linearization approach for modeling of multiphase multi-component flow in porous media

A new approach for the linearization of governing equations that describe flow and transport in porous media is proposed in this work. It is based on an approximate representation of the exact physics of the problem, which is similar to an approximate representation of space and time discretization performed in conventional simulation. The governing equations are introduced as a combination of operators, dependent on spatially altered properties and operators, fully controlled by nonlinear properties of fluid and rock. Next, a parametrization in the physics space of the problem is introduced. The property-based operators are approximated using direct interpolation in the space of nonlinear unknowns. The discrete version of the governing equations is constructed as a combination of operators that approximate both nonlinear physics and discretization in time and space. This approach is applied to the reservoir simulation of miscible and immiscible displacement processes. The performance of the method demonstrates a convergence of simulation results by resolution in physical space with the improved performance.

A crossflow model for an interacting capillary bundle: Development and application for waterflooding in tight oil reservoirs

A new analytical method to calculate crossflow in an interacting capillary bundle has been proposed to analyze immiscible displacement processes in porous media. Capillary force, pressure equilibrium and mass balance were incorporated to develop algebraic equations for crossflow within the interacting bundle respectively before and after water breakthrough. By solving the equations analytically, flow rate in each capillary tube and crossflows among different tubes in the bundle were obtained as a function of water/oil interface positions at different times. The model was then applied to analyze the fluid dynamics of immiscible displacements. The whole process was modelled, from water first entering into the bundle to the moment that no more oil could be further produced. Eight water-displacing-oil cases, including specifically designed scenarios representing a tight reservoir, were modelled in an imbibition process to investigate the effects of pore size distribution, injection rate, and interfacial tension (IFT). The model successfully predicted fingering effect for a tight oil reservoir and even displacement front that could only be achieved by ultra-low IFT. The modelling results are highly consistent with previous experimental and simulation results in the literature. The theoretical model can be used to investigate the effects of different reservoir parameters in immiscible displacement process, such as permeability, wettability, and interfacial tension. The proposed interacting capillary bundle model leads to the pore network simulation in its simplicity as pore connection and topology information is not required.