Pore-scale Phenomena Research Articles

Matrix-fracture transfer shape factor for modeling multimechanisitc multicomponent shale gas flow

Numerical simulation of multimechanisitc multicomponent shale gas flow is computationally intensive and a challenging task. Upscaling of pore scale phenomena to Darcy scale simulations is highly desirable to cut down the computational time. Mass transfer between matrix and fracture in dual-porosity simulators has been traditionally upscaled through a pseudo steady state shape factor, which can be obtained analytically thanks to the linear nature of the pressure diffusion in conventional reservoirs. The use of such a shape factor is well established in modeling of fluid flow and transport in conventional reservoirs. However, the shape factor for multimechanisitc multicomponent shale gas flow is not fully realized and its determination is not straightforward due to the non-linear nature of the governing equations. In this work, we present detailed numerical simulation of multimechanisitc multicomponent shale gas flow to obtain shape factor required for Darcy scale numerical simulation of unconventional reservoirs. It is shown that shape factor can be presented as a function of dimensionless pressure (pseudo pressure), which makes application of transient shape factor independent of time. The dependence of the derived shape factor on pressure drawdown, reservoir temperature, Darcy permeability and fluid composition are also investigated. The theoretical analysis improves our knowledge of shale gas flow dynamics and the results find applications in reservoir simulation of gas production from unconventional reservoirs.

Stabilizing CO2 foams using APTES surface-modified nanosilica: Foamability, foaminess, foam stability, and transport in oil-wet fractured porous media

Foam stability and the improvement of its transport from fracture to matrix have been two major issues in the field of foam injection into fractured petroleum reservoirs as an enhanced oil recovery (EOR) method. In the current study, we have stabilized CO2 foam using surface-modified silica nanoparticles. The modification of nanoparticles was performed using 3-aminopropyltriethoxysilane (APTES). They were characterized by the FTIR analysis and contact angle measurements. After that, foam generation and stability were investigated using static experiments. The experiments were performed at different concentrations of NPs (0.04 to 0.20 mass%), two concentrations of SDS (0.236 and 0.472 mass%), and in the presence and absence of MgCl2 salt. Additionally, the oil recovery and fracture-matrix transport properties of various injected fluids, including CO2 gas, surfactant solution, and NPs stabilized foams were investigated and compared using flooding experiments in a natively oil-wet, fractured micromodel.The results indicate that the surface modification of Silica using the APTES makes the nanoparticles more oil-wet in oil-water system and more gas-wet in air-water system. This, in turn, amplifies the migration of the modified Silica (MS) toward the water-gas interface and enhances the CO2 foam stability. The occurrence of this mechanism could be verified by foam stability experiments, where switching the foam stabilizer from Silica to MS nanoparticles led to a 33.3% increase in the maximum foam half-life. The foamability is not affected by the type of NPs; however, the foaminess is reduced due to the surface adsorption of SDS on the nanoparticle surfaces.Moreover, the stability of foams is reduced in the presence of Mg2+ ions. The reason is investigated utilizing the Mg2+ ion concentration measurements via the atomic adsorption method. Finally, the micromodel flooding indicates that the order of recovery enhancement potential of the CO2 foam stabilizers is SDS-MS > SDS-Silica>SDS. We will discuss the pore-scale phenomena, which lead to such results. We have found that during foam flow in the fractures, the large size bubbles act as viscose fluid and push the relatively smaller bubbles into the matrixes pores. This fracture-matrix transport is followed by the stable foams, and a foam bridge is formed between the fracture and matrix. Additionally, foam front is disintegrated into gas bubbles and water droplets containing surfactants and NPs, which can penetrate the dead-end pores and displace the oil in them through the formation of W/O emulsion.

Density Functional Hydrodynamics in Multiscale Pore Systems: Chemical Potential Drive

We use the method of density functional hydrodynamics (DFH) to model compositional multiphase flows in natural cores at the pore-scale. In previous publications the authors demonstrated that DFH covers many diverse pore-scale phenomena, starting from those inherent in RCA and SCAL measurements, and extending to much more complex EOR processes. We perform the pore-scale modelling of multiphase flow scenarios by means of the direct hydrodynamic (DHD) simulator, which is a numerical implementation of the DFH. In the present work, we consider the problem of numerical modelling of fluid transport in pore systems with voids and channels when the range of pore sizes exceed several orders of magnitude. Such situations are well known for carbonate reservoirs, where narrow pore channels of micrometer range can coexist and interconnect with vugs of millimeter or centimeter range. In such multiscale systems one cannot use the standard DFH approach for pore-scale modeling, primarily because the needed increase in scanning resolution that is required to resolve small pores adequately, leads to a field of view reduction that compromises the representation of large pores. In order to address this challenge, we suggest a novel approach, in which transport in small-size pores is described by an upscaled effective model, while the transport in large pores is still described by the DFH. The upscaled effective model is derived from the exact DFH equations using asymptotic expansion in respect to small-size characterization parameter. This effective model retains the properties of DFH like chemical and multiphase transport, thus making it applicable to the same range of phenomena as DFH itself. The model is based on the concept that the transport is driven by gradients of chemical potentials of the components present in the mixture. This is a significant generalization of the Darcy transport model since the proposed new model incorporates diffusion transport in addition to the usual pressure-driven transport. In the present work we provide several multiphase transport numerical examples including: a) upscaling to chemical potential drive (CPD) model, b) combined modeling of large pores by DFH and small pores by CPD.

Mechanistic Study of Fines Migration in Porous Media Using Lattice Boltzmann Method Coupled With Rigid Body Physics Engine

AbstractThis paper presents a pore-scale model proposed for numerical simulation of fines migration in porous media. The model simulates the behavior of spherical particles with different radii in flow by coupling lattice Boltzmann method (LBM) as a computational fluid dynamics (CFD) solver for the simulation of the fluid flow with a rigid body physics engine responsible for the simulation of the particulate transports. To achieve this, the basic LBM algorithm was extended to treat the curved particle boundaries, and a fluid-particle force interaction was implemented in order to account for the exerted force acting on the particles by the fluid and subsequent particulate movements. The accuracy and reliability of the proposed numerical model were successfully validated by simulating Poiseuille flow and Stokes flow and comparing the simulation results with those of the analytical solution. Thereafter, it was employed to simulate the migration of fine particles through synthetic 2D porous media. The simulation results were also presented to investigate the influence of fines migration on the porosity and permeability of the medium, and more interestingly on the hydraulic tortuosity as a criterion for changes in preferential flow path. As will be shown, the developed numerical method is able to successfully capture major retention mechanisms responsible for fines migration associated formation damage including external cake formation by the large particles, internal cake formation by the small particles, pore plugging, and surface deposition. This work provides a framework for further investigations regarding pore-scale phenomena associated with fines migration in the porous media.

Numerical investigation of surface wettability on gas – Liquid flow hydrodynamics in microchannel: Application to trickle bed reactors

Two-phase gas-liquid flows are very important in trickle bed catalytic reactors. To investigate the effect of catalyst wettability on the two-phase flow hydrodynamics in the bed, microchannels are considered in order to simulate the pore scale phenomena. Since the surface area to volume ratio is a key factor at the microscale, the role of surface interaction becomes dominant. In this work, the channel hydrophobicity is varied in order to study the effect of the wetting properties of a rectangular horizontal micro-channel on the gas-liquid two-phase flow behavior. Air and water are injected through a Y junction microchannel where water is injected in the middle and air from side inlets, to investigate the air/water two-phase flow behavior in the straight section. The surface wettability of two types of catalysts is experimentally measured and used as input to the numerical computational model. The microchannel is of 300 μm, 100 μm and 1 cm in width, height and length, respectively. The CFD simulation is done on COMSOL Multiphysics, using the Level Set method. The level-set technique is used to represent a discrete fluid interface between the two phases. Navier Stokes equations and conservation of mass, coupled to the level set method keep track of the interface between the air and water in the flow field, including the interfacial interactions with the microchannel walls. The developed numerical model is used to characterize the hydrodynamics of cocurrent gas—liquid flow through the microchannel. The model was validated against published experimental data and good agreements are obtained. The prediction results demonstrate that the wetting properties of the microchannel affect drastically the two-phase flow hydrodynamic behaviors. We identified eight different flow patterns in the hydrophobic microchannel, whereas, in the case of hydrophilic microchannel, only two flow patterns were observed. All of these results were in good agreement with published experimental ones. The developed numerical model was thus used to predict trickle bed flow hydrodynamics at the microscale.

A microfluidic experiment and pore scale modelling diagnostics for assessing mineral precipitation and dissolution in confined spaces

Dissolution and precipitation processes control fundamental properties of porous media in the subsurface such as porosity and permeability thus affecting ground water flow and solute transport. These processes occur at different time and length scales, and are often not easily captured by a single macroscopic continuum scale reactive transport model. Precipitation of even small amounts of solid phases along the major transport pathways may result in substantial change of rock permeability. A mechanistic description of these processes in the pore space is therefore a prerequisite. In order to bridge atomistic and macroscopic scales, it is necessary to understand the processes and subsequently to upscale the pore-scale results to macroscopic simulation codes. In this direction, we develop a methodology combining a sophisticated microfluidic experimental setup and multiscale modelling numerical diagnostics. This allows exploring the processes of mass transport coupled to nucleation, mineral precipitation and dissolution in confined space. For this purpose, a system with relatively few chemical species, but with well-defined kinetic parameters was chosen. As a result of the advective and diffusive mixing of solutions of Sr2+ and SO42− ions, celestine precipitated inside the microfluidic chambers. The reactions inside the microfluidic experiment were marked by 4 stages: the induction period, the crystal growth, the clogging which prevented the mixing of the reactant solutions, and finally the dissolution of celestine crystals. The growth and dissolution rates of celestine inside the chambers were found to be in good agreement with literature data obtained in bulk experiments. The pore scale modelling of the processes inside the microfluidic reactor was based on the Lattice Boltzmann method and was used to spatially resolve the solution composition (not accessible experimentally), to predict the induction time, and to calculate the local saturation indices using full speciation. The information gained from the cross-scale pore-level model helped to gain insights into the underlying processes and to explain the preferential growth direction of the crystals during the experiment. The combination of microfluidic lab-on-chip experiments with complementary multiphysics numerical diagnostics is a promising methodology to provide insights into pore scale phenomena, to optimize the design of experiments and to parameterize appropriate constitutive equations for coupled processes in porous media.

Investigating fouling at the pore-scale using a microfluidic membrane mimic filtration system

The work investigates fouling in a microfluidic membrane mimic (MMM) filtration system for foulants such as polystyrene particles and large polymeric molecules. Our MMM device consists of a staggered arrangement of pillars which enables real-time visualization and analysis of pore-scale phenomena. Different fouling scenarios are investigated by conducting constant-pressure experiments. Fouling experiments are performed with three different types of foulants: polystyrene particle solution (colloidal fouling), polyacrylamide polymer solution (organic fouling) and a mixture of these two solutions (combined fouling). Four major categories of microscopic fouling are observed: cake filtration (upstream), pore blocking (inside the pores), colloidal aggregation (downstream) and colloidal streamer fouling (downstream). Our microfluidic experiments show that downstream colloidal aggregation and streamer fouling have a significant effect on overall membrane fouling which were not studied before.

Towards pore network modelling of spontaneous imbibition: contact angle dependent invasion patterns and the occurrence of dynamic capillary barriers

Imbibition is an important process encountered in many porous media applications. At the pore scale, pore network models (PNM) are computationally efficient and can model drainage accurately. However, using PNM to model imbibition still remains a challenge due to the complexities encountered in understanding pore-scale flow phenomena related to pore body filling (PBF) and snap-off along with the relative competition between these events. In this work, we use direct numerical simulations (DNS) to revisit the basic principles of PBF in a two-dimensional synthetic pore geometry. We notice that PBF during spontaneous imbibition is dependent on several parameters such as shape of the transition zone, contact angle and the fluid properties like density. The interactions between these parameters are investigated in a quantitative manner. We demonstrate the existence of a critical contact angle \U0001d703c and a barrier contact angle \U0001d703b. \U0001d703c depends on the shape of the pore geometry, whereas \U0001d703b depends on the pore geometry, contact angle and fluid properties. For a system comprising of light fluids, \U0001d703b is only slightly larger than \U0001d703c; whereas for a system occupied by dense fluids, \U0001d703b is notably larger than \U0001d703c. The contact angle of the wetting phase \U0001d703 in relation to \U0001d703c and \U0001d703b decides if the wetting phase can imbibe a pore body. Imbibition always occurs if \U0001d703 < \U0001d703c. For \U0001d703 > \U0001d703c, we observe capillary barrier zones in which capillary forces accompany viscous forces to resist spontaneous imbibition. For this case, we observe smooth transition of the meniscus curvature while the meniscus enters and exits capillary barrier zones. For \U0001d703c ≤ \U0001d703 ≤ \U0001d703b, inertia assists the wetting phase to overcome resisting forces and imbibe the pore space. For \U0001d703 > \U0001d703b, the resisting forces dominate over inertia so that the wetting phase cannot imbibe the pore space. For the synthetic pore geometries investigated, we provide analytical and semi-analytical expressions to determine \U0001d703c and the position of capillary barrier zones respectively. The barrier contact angle \U0001d703b is computed numerically for several inertial systems and for various shapes of the synthetic pore geometry. The results of this quantitative analysis can be utilised to improve the existing pore filling rules and predictive capabilities of PNM used for two-phase flows.

On the development of a relative permeability equation of state

Standard compositional simulators use composition-dependent cubic equations of state (EoS), but saturation-dependent relative permeability and capillary pressure. This discrepancy causes discontinuities, increasing computational time and reducing accuracy. In addition, commonly used empirical correlations, such as the Corey relative permeability model, show a sole dependence of relative permeability on phase saturation, lumping the effect of other pore-scale phenomena into one tuning exponent. To rectify this problem, relative permeability has been recently defined as a state function, so that it becomes compositional dependent and single valued. Such a form of the relative permeability EoS can significantly improve the convergence in compositional simulation for both two- and three-phase flows. This paper revisits the recently developed EoS for relative permeability by defining relevant state variables and deriving functional forms of the partial derivatives in the state function. The state variables include phase saturation, phase connectivity, wettability index, capillary number, and pore topology. The developed EoS is constrained to key physical boundary conditions. The model coefficients are estimated through linear regression on data collected from a pore-scale simulation study that estimates relative permeability based on micro-CT image analysis. The results show that a simple quadratic expression with few calibration coefficients gives an excellent match to two-phase flow simulation measurements from the literature. The goodness of fit, represented by the coefficient of determination (R2) value, is 0.97 for relative permeability at variable phase saturation and phase connectivity, and constant wettability, pore structure, and capillary number (∼ 10− 4). The quadratic response for relative permeability also shows excellent predictive capabilities.

Pore-level visual analysis of heavy oil recovery using chemical-assisted waterflooding process – Use of a new chemical agent

Chemical-assisted waterflooding enhances the ultimate recovery of a conventional waterflooding process through several mechanisms such as reducing interfacial tension between water and oil, formation of in-situ emulsions, treatment of adverse mobility ratio, and wettability modification. Application of chemical-assisted waterflooding for recovery of heavy oil is still an active research topic. A new chemical technology (i.e. IPC Technology as referred to in this paper) has been developed. A proprietary mixture of surfactants is used in several techniques associated with surface extraction as well as in-situ recovery of heavy oil and bitumen. This formulation of solvents and surfactants is reusable, low foaming, non-flammable, not acutely toxic, and non-carcinogenic. The efficacy of using IPC as an additive for waterflooding was presented earlier through a systematic coreflooding study, which showed increased ultimate recovery of different types of oils when compared with commercial surfactant and alkali flooding. In order to investigate the mechanisms behind the enhanced macro-scale oil recovery, a series of pore-scale tests were designed and conducted in this study. Glass micromodel type of porous media was used in the presence of brines with different ion compositions. The pore-scale chemical-assisted waterflooding tests were carried out in four consecutive stages: brine flooding, chemical flooding, soaking period, and extended brine flooding. High quality pore-scale images were captured for qualitative and quantitative analysis of the IPC-assisted waterflooding at the pore-level. IPC intensified water wettability of grain particles in the presence of NaCl; however in the presence of MgCl2, use of IPC makes solid surfaces oil-wet. The phenomenon of water-in-oil and oil-in-water emulsification was observed when IPC was used along with different brine compositions. This phenomenon is weakened for lighter oils. When the acid number of the oil was low, extension of soaking period intensified wettability alteration and emulsification mechanisms. Other pore-scale phenomena were also observed during visualization tests such as coalescence of microdroplets during the extended waterflooding stage, snap-off mechanism creating daughter droplets during the extended waterflooding stage, occasional flow of bulk oil films toward the production end, and wettability reversal during various flooding stages. Attempts were also made to conduct statistical analysis of emulsion droplet sizes under different test conditions. Several parameters, including chemical concentration as well as ion concentration in brines, were found to significantly affect the emulsion droplet size distribution.

Measurements of capillary pressure and relative permeability curves for foam transport in porous media-A capillary bundle approach

Foam mobility in porous media is governed by bubble texture, foam trapping, bubble generation, and bubble coalescence. Published reports showed that foam mobility is dominated by foam trapping in the transient flow regime or low capillary pressures (Pc), while bubble coalescence dominates foam flow in the steady state regime or higher Pc. An efficient foam model is expected to capture all these pore scale phenomena. However, most of the available models do not adequately account for foam trapping behavior because their model parameters are usually determined from coreflood experiments at steady state flow regimes. Hence, they are unsuitable for simulating transient foam flow behavior. Some mechanistic population balance models incorporate the effect of foam trapping on gas mobility through the relative permeability (Kr) function such that the Kr of the flowing foam is a function of only the flowing foam saturation. However, a constitutive equation is required to predict the flowing foam fraction. Some of the variables in this equation are also obtained from experimental data at steady state, while there is no known experimental method to measure other variables. In this paper, a novel coreflood method is presented that allows flowing foam fraction to be measured directly at different Pc and water saturations during foam flow. A consolidated porous medium was treated like a bundle of capillaries of various sizes, by modifying the surfactant alternating gas (SAG) method of foam injection. An electrical resistivity tool monitored in-situ saturation changes while a high resolution pressure transducer measured the pressure drop across rock samples. Multiple SAG cycles generated a data array of trapped and flowing foam as a function of water saturation and capillary pressure, which was then used to generate Pc and Kr curves. The Pc and Kr curves exhibit behavior that are consistent with established physics of foam flow in porous media. The measured Pc curves also compared well with porous plate Pc measurements, which thus validates the accuracy of the methodology in treating a consolidated porous medium as a bundle of capillaries. The measured foam limiting capillary pressure values also showed a good trend with those reported in the literature. The critical water saturation for foam was much higher than the connate water saturation measured from the porous plate method. Finally, it was shown that this method has a strong potential to be implemented at a field scale.

Evaluation of foam generated with the hydrocarbon solvent for extra-heavy oil recovery from fractured porous media: Pore-scale visualization

Aqueous based foam injection has gained interest for conventional oil recovery in recent times. Foam can control the mobility ratio and improve the sweep efficiency in oil reservoirs over gas flooding. However, due to the high viscosity of the oil, its application in heavy oil reservoirs is challenging. Moreover, the oil-wet nature of carbonate reservoirs makes it difficult for aqueous based foam to efficiently remove the heavy oil. On the other hand, hydrocarbon solvents have been used for decreasing the heavy oil viscosity and increase its recovery by diffusion and mixing mechanisms. However, the low rate of diffusion/dispersion, inadequate sweep efficiently and asphaltene precipitation, especially in heterogeneous reservoirs, are the major challenges during solvent injection. In this paper, hydrocarbon solvent based foam (SBF) as an alternative to solvent flooding is explored for heavy oil recovery from a fractured porous media.Hydrocarbon solvent-based CO2 foam was used to increase sweep efficiency during heavy oil recovery. The foam was generated with the help of a fluorosurfactant in a hydrocarbon solvent. Static bulk performances of foam were analyzed at different concentrations of surfactant. Surface tension measurements were also performed to study the adsorption of surfactant into the liquid-gas interface and its effect on foamability and foam stability. A specially designed fractured micromodel (oil wet, representing fractured carbonate reservoirs) was used to visualize the pore-scale phenomena during solvent based foam injection. For the first time, extra heavy oil with a viscosity of about 30,000 cp has been used in this study for pore scale visualization. A high-quality camera was utilized to capture images/movies.According to static experiments, although the value of the surface tension of hydrocarbon solvent was initially low, the addition of surfactant slightly decreased the surface tension further improving the foam stability. However, the mechanisms involved in foamability and foam stability of non-aqueous based foam are more complicated than water based foam and cannot be discussed solely based on surface tension and bulk analysis. In addition, dynamic pore scale observation through this study revealed that solvent based foam can significantly contribute to heavy oil recovery with different mechanisms. At the initial stage, solvent diffuses and mixes with viscous oil and reduce the viscosity. Later, foam bubbles improve the sweep efficiency by diverting the solvent toward the untouched part of the porous media. Foam bubbles partially blocked the larger pores in matrix/swept-area increasing the contact of solvent and heavy oil, providing better mixing. Therefore, oil is swept much faster and more efficiently from the grain in oil-wet porous media compared to that of conventional solvent flooding.

A combined method for pore-scale optical and thermal characterization of SAGD

Steam-assisted gravity drainage (SAGD) is an important oil recovery strategy for extra heavy oil and bitumen. Operators are under pressure to improve both the environmental and economic performance of SAGD. Through direct visualization, micromodels provide insight into SAGD, but methods to date cannot fully resolve the temperature field which is essential to this thermal recovery process. In this work, infrared and optical pore-scale imaging of the SAGD process within a micromodel with reservoir-relevant pore geometries, fluids, and temperatures was performed, and both recovery and pore-scale fluid behavior was quantified for different concentrations of alkaline additive. Combined microscale flow and high-resolution temperature analysis provide insight into pore-scale phenomena, and shed light on the link between the rapid temperature drop at the steam chamber interface, drainage modes, efficiency and ultimate recovery achieved in SAGD.

Post-Surfactant $$\hbox {CO}_{2}$$ CO 2 Foam/Polymer-Enhanced Foam Flooding for Heavy Oil Recovery: Pore-Scale Visualization in Fractured Micromodel

Carbonate reservoirs hold significant reserves of heavy crude oil that can be recovered by nonthermal processes. Chemical-enhanced oil recovery from oil-wet carbonate reservoirs has focused on the use of surfactants to change wettability and enhance imbibition into the matrix; however, the fractured nature of carbonate formations makes oil recovery a challenging process. Recently, developments in foam/polymer-enhanced foam (PEF) injection for heavy oil recovery application have come about, but the process of PEF for carbonate reservoirs is still not fully understood. This paper introduced a new approach to accessing the heavy oil from fractured carbonate reservoirs. \(\hbox {CO}_{2}\) foam/PEF was used to decrease oil saturation after surfactant flooding. Three types of surfactants (nonionic, anionic, and cationic) were used for both surfactant and foam flooding. A specially designed fractured micromodel representing a porous media system was used to visualize pore-scale phenomena. In addition, the static performances of foam/PEF were analyzed in the presence of heavy crude oil. The results showed that in both static and dynamic studies, the PEF had higher stability than the foam. Nonionic surfactant generated the least stable foam in the presence of crude oil. Surfactant flooding slightly increased the oil recovery from matrix after water injection. This was more evident in the case of cationic surfactant with highest imbibition rate. Observation through this study proved that stable foam/PEF bubbles can significantly push the injected fluid toward untouched parts of the porous media and increased the oil recovery. Due to the liquid viscosity enhancement and bubble stability improvement, the effectiveness of PEF in heavy oil sweep efficiency was much higher than that of conventional foams. PEF bubbles generated an additional force to divert surfactant/polymer into the matrix.

New Insight on Carbonate-Heavy-Oil Recovery: Pore-Scale Mechanisms of Post-Solvent Carbon Dioxide Foam/Polymer-Enhanced-Foam Flooding

Summary Carbonate reservoirs, deposited in the Western Canadian Sedimentary Basin (WCSB), hold significant reserves of heavy crude oil that can be recovered by nonthermal processes. Solvent, gas, water, and water-alternating-gas (WAG) injections are the main methods for carbonate-heavy-oil recovery in the WCSB. Because of the fractured nature of carbonate formations, many advantages of these production methods are usually in contrast with their low recovery factor. Alternative processes are therefore needed to increase oil-sweep efficiency from carbonate reservoirs. Foam/polymer-enhanced-foam (PEF) injection has gained interest in conventional heavy-oil recovery in recent times. However, the oil-recovery process by foam, especially PEF, in conjunction with solvent injection is less understood in fractured heavy-oil-carbonate reservoirs. The challenge is to understand how the combination of surfactant, gas, and polymer allows us to better access the matrix and efficiently sweep the oil. This study introduces a new approach to access the unrecovered heavy oil in fractured-carbonate reservoirs. Carbon dioxide (CO2) foam and CO2 PEF were used to decrease oil saturation after solvent injection, and their performance was compared with gas injection. A specially designed fractured micromodel was used to visualize the pore-scale phenomena during CO2-foam/PEF injection. In addition, the static bulk performances of CO2 foam/PEF were analyzed in the presence of heavy crude oil. A high-definition camera was used to capture high-quality images. The results showed that in both static and dynamic studies the PEF had high stability. Unlike CO2 PEF, CO2 foam lamella broke much faster and resulted in the collapse of the foam during heavy-oil recovery after solvent flooding. It appeared that foam played a greater role than just gas-mobility control. Foam showed outstanding improvement in heavy-oil recovery over gas injection. The presence of foam bubbles was the main reason to improve heavy-oil-sweep efficiency in heterogeneous porous media. When the foam bubbles advanced through pore throats, the local capillary number increased enough to displace the emulsified oil. PEF bubbles generated an additional force to divert surfactant/polymer into the matrix. Overall, CO2 foam and PEF remarkably increased heavy-oil recovery after solvent injection into the fractured reservoir.

Hybrid multiscale simulation of a mixing-controlled reaction

Continuum-scale models, which employ a porous medium conceptualization to represent properties and processes averaged over a large number of solid grains and pore spaces, are widely used to study subsurface flow and reactive transport. Recently, pore-scale models, which explicitly resolve individual soil grains and pores, have been developed to more accurately model and study pore-scale phenomena, such as mineral precipitation and dissolution reactions, microbially-mediated surface reactions, and other complex processes. However, these highly-resolved models are prohibitively expensive for modeling domains of sizes relevant to practical problems. To broaden the utility of pore-scale models for larger domains, we developed a hybrid multiscale model that initially simulates the full domain at the continuum scale and applies a pore-scale model only to areas of high reactivity. Since the location and number of pore-scale model regions in the model varies as the reactions proceed, an adaptive script defines the number and location of pore regions within each continuum iteration and initializes pore-scale simulations from macroscale information. Another script communicates information from the pore-scale simulation results back to the continuum scale. These components provide loose coupling between the pore- and continuum-scale codes into a single hybrid multiscale model implemented within the SWIFT workflow environment. In this paper, we consider an irreversible homogeneous bimolecular reaction (two solutes reacting to form a third solute) in a 2D test problem. This paper is focused on the approach used for multiscale coupling between pore- and continuum-scale models, application to a realistic test problem, and implications of the results for predictive simulation of mixing-controlled reactions in porous media. Our results and analysis demonstrate that the hybrid multiscale method provides a feasible approach for increasing the accuracy of subsurface reactive transport simulations.

Pore-scale simulation of multicomponent multiphase reactive transport with dissolution and precipitation

Multicomponent multiphase reactive transport processes with dissolution–precipitation are widely encountered in energy and environment systems. A pore-scale two-phase multi-mixture model based on the lattice Boltzmann method (LBM) is developed for such complex transport processes, where each phase is considered as a mixture of miscible components in it. The liquid–gas fluid flow with large density ratio is simulated using the multicomponent multiphase pseudo-potential LB model; the transport of certain solute in the corresponding solvent is solved using the mass transport LB model; and the dynamic evolutions of the liquid–solid interface due to dissolution–precipitation are captured by an interface tracking scheme. The model developed can predict coupled multiple physicochemical processes including multiphase flow, multicomponent mass transport, homogeneous reactions in the bulk fluid and heterogeneous dissolution–precipitation reactions at the fluid–solid interface, and dynamic evolution of the solid matrix geometries at the pore-scale. The model is then applied to a physicochemical system encountered in shale gas/oil industry involving multiphase flow, multicomponent reactive transport and dissolution–precipitation, with several reactions whose rates can be several orders of magnitude different at a given temperature. The pore-scale phenomena and complex interaction between different sub-processes are investigated and discussed in detail.

Anomalous porosity preservation and preferential accumulation of gas hydrate in the Andaman accretionary wedge, NGHP-01 site 17A

In addition to well established properties that control the presence or absence of the hydrate stability zone, such as pressure, temperature, and salinity, additional parameters appear to influence the concentration of gas hydrate in host sediments. The stratigraphic record at Site 17A in the Andaman Sea, eastern Indian Ocean, illustrates the need to better understand the role pore-scale phenomena play in the distribution and presence of marine gas hydrates in a variety of subsurface settings. In this paper we integrate field-generated datasets with newly acquired sedimentology, physical property, imaging and geochemical data with mineral saturation and ion activity products of key mineral phases such as amorphous silica and calcite, to document the presence and nature of secondary precipitates that contributed to anomalous porosity preservation at Site 17A in the Andaman Sea. This study demonstrates the importance of grain-scale subsurface heterogeneities in controlling the occurrence and distribution of concentrated gas hydrate accumulations in marine sediments, and document the importance that increased permeability and enhanced porosity play in supporting gas concentrations sufficient to support gas hydrate formation. The grain scale relationships between porosity, permeability, and gas hydrate saturation documented at Site 17A likely offer insights into what may control the occurrence and distribution of gas hydrate in other sedimentary settings.

Pore-scale simulation of coupled multiple physicochemical thermal processes in micro reactor for hydrogen production using lattice Boltzmann method

A general numerical scheme based on the lattice Boltzmann method (LBM) is established to investigate coupled multiple physicochemical thermal processes at the pore-scale, in which several sets of distribution functions are introduced to simulate fluid flow, mass transport, heat transfer and chemical reaction. Interactions among these processes are also considered. The scheme is then employed to study the reactive transport in a posted micro reactor. Specially, ammonia (NH3) decomposition, which can generate hydrogen (H2) for fuel of proton exchange membrane fuel cells (PEMFCs), is considered where the endothermic decomposition reaction takes place at the surface of posts covered with catalysts. Simulation results show that pore-scale phenomena are well captured and the coupled processes are clearly predicted. Effects of several operating and geometrical conditions including NH3 flow rate, operating temperature, post size, post insert position, post orientation, post arrangement and post orientation on the coupled physicochemical thermal processes are assessed in terms of NH3 conversion, temperature uniformity, H2 flow rate and subsequent current density generated in PEMFC.

Dynamic Nonequilibrium of Water Flow in Porous Media: A Review

This review provides an overview on various phenomena, hypothesized causes, and modeling approaches that describe “dynamic nonequilibrium” (DNE) of water flow in soils. Dynamic nonequilibrium is characterized from observations on the macroscale by an apparent flow-rate dependence of hydraulic properties or by local nonequilibrium between water content and pressure head under monotonic imbibition or drainage histories, i.e., not affected by traditional hysteresis. The literature indicates that key processes causing DNE are pore-scale phenomena such as relaxation of air–water-interface distributions, limited air-phase permeability, dynamic contact angles, and time-dependent wettability changes. Furthermore, entrapment of water and pore water blockage, air-entry effects, and temperature effects might be involved. These processes act at different pressure head regions and on different time scales, which makes effective modeling of the combined phenomena challenging. On larger scales, heterogeneity of soil properties can contribute to DNE observations. We conclude that there is an urgent need for precision measurements that are designed to quantify dynamic effects.