Displacement Processes In Porous Media Research Articles

Pore-scale study of three-dimensional three-phase dynamic behaviors and displacement processes in porous media

Carbon dioxide geological sequestration is a key method to alleviate global warming and enhance oil recovery, where the three-phase displacement processes of oil, water, and carbon dioxide gas in porous media are frequently encountered. In this study, a three-phase three-dimensional lattice Boltzmann method coupled with special wettability and outlet boundary schemes is adopted to simulate the three-phase displacement processes in porous media. The method is validated by the contact angles on a curved surface and droplet flowing through the outlet boundary. With this method, the influences of capillary number, wettability, and local large pores on three-phase flow are investigated. In particular, different dynamic behaviors of fluids are observed at the pore scale, such as bypass-double displacement, stop-wait displacement, burst displacement, snap-off trapping, and corner flow. Further, Euler number and oil saturation are calculated to quantitatively characterize the fluidic morphology and displacement efficiency under different conditions. For all three phases, the Euler number of low capillary number, strong water-wet, and structures with large and medium pores is relatively low, indicating that the morphology of fluids is more connective. For enhancing oil recovery efficiency, high capillary number and strong water-wet structures are beneficial.

Wetting and pressure gradient performance in a lattice Boltzmann color gradient model

An accurate implementation of wetting and pressure drop is crucial to correctly reproduce fluid displacement processes in porous media. Although several strategies have been proposed in the literature, a systematic comparison of them is needed to determine the most suitable for practical applications. Here, we carried out numerical simulations to investigate the performance of two widely used wettability schemes in the lattice Boltzmann color gradient model, namely, the geometrical wetting scheme by Leclaire et al. [Phys. Rev. E 95(3), 033306 (2017)](scheme-I) and the modified direction of the color gradient scheme by Akai et al. [Adv. Water Resour. 116, 56–66 (2018)] (scheme-II). We showed that scheme-II was more accurate in simulating static contact angles of a fluid droplet on a solid surface. However, scheme-I was more accurate in simulating a dynamic case of a binary fluid flow in a horizontal capillary tube described by the Washburn equation. Moreover, we investigated the performance of two popular pressure gradient implementation types. Type-I used the so-called Zou–He pressure boundary conditions at the inlet and the outlet of the domain, while type-II used an external body force as a pressure gradient. We showed that the type-I implementation was slightly more accurate in simulating a neutrally wetting fluid in a horizontal capillary tube described by the Washburn equation. We also investigated the differences between the two types of pressure gradient implementation in simulating two fluid displacement processes in a Bentheimer sandstone rock sample: the primary drainage and the imbibition displacement processes.

Implementation of a direct-addressing based lattice Boltzmann GPU solver for multiphase flow in porous media

GPU accelerated lattice Boltzmann (LB) simulations of multiphase flow in porous media have become a powerful tool to study fluid displacement process in porous media. For porous structures with a very low porosity, indirect-addressing memory access methods are preferred due to significantly reduction of the memory footprint despite that those methods are more difficult to implement and the resulting performance may be more sensible to the computing architectures, such as cache hierarchy and size. The direct-addressing methods are straightforward to implement and are able to archive high throughput when the porosity is large, while the methods become less efficient when the structures are too sparse. Nevertheless, the direct-addressing methods combined with multi-block grid technique are promising for many applications. In this work, we present a hybrid-way to tackle multiphase flow simulations in porous media, where the direct-addressing method is employed for the main LB evolution while the indirect-addressing method is employed for the complex boundary conditions. The CSF-based LB color-gradient multiphase model and the geometry-based wetting model are employed to increase accuracy and stability. Thanks to the utilization of AA-pattern streaming scheme, non-slip boundary condition of arbitrary orientation can be enforced without extra cost. We perform comprehensive analysis of the computational performance of the present solver on NVIDIA GPUs. For typical sandstones, our results show that the present implementation is able to achieve over 1.5 speedup compared with other direct-addressing schemes on V100 and A100, respectively and, particularly, the computational performance of the boundary kernels is greatly increased thanks to the increased L2 cache size of the latest GPUs.

Effects of macro-scale heterogeneity on the kinetic interface-sensitive tracer test for measuring the fluid–fluid interfacial area in dynamic two-phase flow in porous media

A novel reactive smart tracer method, termed the kinetic interface-sensitive (KIS) tracer test, has been demonstrated in laboratory column experiments to enable measurement of the specific capillary-associated fluid–fluid interfacial area in dynamic two-phase flow displacement processes in porous media. Development of the tracer method towards effective application in real field conditions requires investigation of the influence of the porous media heterogeneity on the front size and the specific interfacial area, and, consequently, in how far a kinetic interface-sensitive tracer experiment, and the corresponding breakthrough curves, are affected. This study employs a two-dimensional Darcy-scale two-phase flow reactive transport model to investigate numerically the KIS tracer transport in heterogeneous porous media. Simulations were carried out for the primary drainage process in a domain formed of fine and coarse porous media. Various heterogeneity patterns, having different numbers of inclusions and different geometrical distributions, were studied. It is shown that the shape of the breakthrough curves can be used as an indicator for quantifying the displacement front roughness, the specific interfacial area in the domain, and the domain heterogeneity, e.g., the existence of preferential flow pathways inside the porous media. The results indicate that when the displacement front roughness is small, the concentration breakthrough curves exhibit a linear increase. The slopes of the breakthrough curves linearly depend on the fraction of the bulk volume occupied by the low-permeability sand inclusions. The volume-averaged specific interfacial area and the size of the transition zone can be determined from the slopes of the breakthrough curves.

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.

Effect of viscoelasticity on displacement processes in porous media

Improving the displacement efficiency of capillary entrapments in porous media by adding high molecular weight polymers to the invading phase has various industrial applications, from enhanced oil recovery to soil remediation. Apart from an increased viscosity contrast compared to regular water flooding, the flow of viscoelastic polymer solutions exhibits unstable flow behavior even at small Reynolds numbers, which can lead to an additional displacement mechanism of the capillary entrapments. In this work, we employ a microfluidic approach to unravel the underlying physics and mechanism of this enhanced pore scale displacement. To this end, we show that the major complex topological flow features in a typical porous medium can be mimicked by a flow geometry consisting of a single capillary entrapment connected to two symmetric serpentine channels. This design excludes the effect of viscous stresses and allows direct focus on displacement processes driven solely by elastic stresses. We show that the unique viscoelastic fluid features, such as the significant storage and release of elastic stresses and first normal stress difference, combined with the flow geometry, lead to purely elastic instability and secondary flow, which in turn provide the stresses necessary to overcome the capillary threshold and displace the capillary entrapment.

Visual Analysis of Displacement Processes in Porous Media using Spatio-Temporal Flow Graphs.

We developed a new approach comprised of different visualizations for the comparative spatio-temporal analysis of displacement processes in porous media. We aim to analyze and compare ensemble datasets from experiments to gain insight into the influence of different parameters on fluid flow. To capture the displacement of a defending fluid by an invading fluid, we first condense an input image series to a single time map. From this map, we generate a spatio-temporal flow graph covering the whole process. This graph is further simplified to only reflect topological changes in the movement of the invading fluid. Our interactive tools allow the visual analysis of these processes by visualizing the graph structure and the context of the experimental setup, as well as by providing charts for multiple metrics. We apply our approach to analyze and compare ensemble datasets jointly with domain experts, where we vary either fluid properties or the solid structure of the porous medium. We finally report the generated insights from the domain experts and discuss our contribution's advantages, generality, and limitations.

Pore-scale study of three-phase displacement in porous media

Carbon capture, utilization, and storage have been an effective way to deal with global climate issues. Injecting CO2 into depleted oil reservoirs can reach the dual goal of carbon storage and enhanced oil recovery. To optimize the gas injection strategy, it is necessary to understand the underlying mechanisms of three-phase fluid flow of oil, water, and gas. In this study, a lattice Boltzmann color gradient model is used to investigate the pore-scale three-phase displacement process in porous media. Gas is injected into the porous domain initially occupied by water and oil. Typical microscopic behaviors, including coalescence and split-up, pinch-off, double and multiple displacement, as well as parallel flow, are identified and discussed. Effects of water content (ϕ), capillary number (Ca), wettability and viscosity ratio (M) on the flow pattern, and oil recovery rate are explored. The oil ganglia inhibit the development of gas fingers, causing stronger viscous fingering characteristics with increasing ϕ. The fingering pattern is located in the crossover zone for the Ca from 5 × 10−5 to 5 × 10−4. As ϕ increases, the oil recovery rate reduces. The oil ganglia tend to occupy small pores as oil wettability enhanced, making it more difficult to be drained out. The reduction of oil viscosity is beneficial to improve connectivity, thereby effectively enhancing the oil recovery. Finally, the CO2 storage rate is also evaluated. It is found that the storage rate is very sensitive to the initial oil–water distributions. In general, the storage rate increases as ϕ decreases, Ca increases, and oil wettability enhances.

A pore-resolved interface tracking algorithm for simulating multiphase flow in arbitrarily structured porous media

We present an interface tracking algorithm that incorporates essential pore-scale invasion mechanisms for simulating multiphase flow in porous media in capillary dominated regime. The algorithm allows the capture of the actual shape of porous medium with complex geometrical features, including both convex and concave particles or irregular channels. It also incorporates the sharp edge pinning effect such that pinning of menisci at corners can be naturally taken into account. We firstly conduct simulations under imbibition and drainage conditions in a single junction micro-model and in disordered porous media for validation. It is shown that the invasion mechanisms at pore scale are accurately captured, and the macroscopic invasion morphology in porous media are reproduced. A series of simulations for fluid displacement processes are carried out across a wide range of intrinsic contact angles in a two-dimensional representation of a Berea sandstone. The transition between stable displacement and capillary fingering is characterized using displacement efficiency, fractal dimension, and fluid–fluid interfacial length. This work deepens the understanding of fluid–fluid displacement processes in porous media. Furthermore, the presented interface tracking algorithm offers a highly efficient tool for further exploration of effects of wettability, geometry, and topology on multiphase flow in realistic porous materials.

Visual Analysis of Two‐Phase Flow Displacement Processes in Porous Media

AbstractWe developed a new visualization approach to gain a better understanding of the displacement of one fluid phase by another in porous media. This is based on a recent experimental parameter study with varying capillary numbers and viscosity ratios. We analyse the temporal evolution of characteristic values in this two‐phase flow scenario and discuss how to directly compare experiments across different temporal scales. To enable spatio‐temporal analysis, we introduce a new abstract visual representation showing which paths through the porous medium were occupied and for how long. These transport networks allow to assess the impact of different acting forces and they are designed to yield expressive comparability and linking to the experimental parameter space both supported by additional visual cues. This joint work of porous media experts and visualization researchers yields new insights regarding two‐phase flow on the microscale, and our visualization approach contributes towards the overarching goal of the domain scientists to characterize porous media flow based on capillary numbers and viscosity ratios.

Multidimensional scaling analysis of mixing displacement processes in porous media

W pracy podjęto próbę zastosowania teorii podobieństwa do modelowania badań laboratoryjnych wykonanych na tzw. długich rdzeniach wiertniczych. Wykorzystane w ramach pracy badania laboratoryjne obejmowały wypieranie ropy zatłaczanym dwutlenkiem węgla oraz siarkowodorem. Do analizy pod kątem zjawiska skalowania wykorzystano dziewięć eksperymentów – pięć wybranych badań dotyczyło wypierania ropy dwutlenkiem węgla, a pozostałe cztery wypierania ropy przy zastosowaniu siarkowodoru jako medium wypierającego. W pierwszym etapie realizacji pracy zbudowano modele symulacyjne wybranych eksperymentów w celu określenia parametrów mieszania się płynów, a w szczególności określenia współczynnika dyspersji fizycznej. Korzystając z uzyskanych wyników, sporządzono pełną listę parametrów opisujących zjawisko wypierania mieszającego zachodzące w eksperymentach. Wykonano analizę wymiarową i przy użyciu twierdzenia Buckinghama wygenerowano zestawy liczb podobieństwa opisujące to zjawisko. Wybrano jeden z wygenerowanych zestawów liczb podobieństwa właściwy dla ich porównania z jednowymiarowym modelem matematycznym opisującym zjawisko wypierania mieszającego wyrażonego w postaci równań o bezwymiarowych zmiennych niezależnych i bezwymiarowych współczynnikach. Zidentyfikowano współczynniki tych równań z wcześniej wygenerowanymi liczbami podobieństwa oraz określono pozostałe liczby podobieństwa niewystępujące w tych równaniach. Celem szczegółowej analizy wyników eksperymentów przeprowadzono ich parametryzację, wykorzystując wielomiany Padégo jako najprostsze efektywne modele interpolacyjne tych wyników. W konsekwencji analizowano zależność wyników eksperymentów w postaci powyższych parametrów od poszczególnych liczb podobieństwa. Potwierdzono dominującą zależność wyników eksperymentów wypierania mieszającego od liczb podobieństwa występujących jako bezwymiarowe współczynniki w równaniach opisujących modele jednowymiarowe tego procesu. Zbadano wpływ grawitacji na efektywne modelowanie procesu wypierania mieszającego jako zjawiska świadczącego o wielowymiarowości analizowanego procesu poprzez zastosowanie modeli trójwymiarowych oraz ich redukcję do postaci jednowymiarowej z użyciem efektywnej stałej dyspersji. Przedstawiono założenia i wyniki takiego modelowania. Wykorzystano je do wyznaczenia stałej dyspersji poprzecznej do kierunku procesu wypierania poprzez ich zastosowanie do analizy eksperymentów wypierania różniących się wydajnością zatłaczanego płynu.

NUMERICAL INVESTIGATION OF COUPLED ANOMALOUS DIFFUSION AND HEAT TRANSFER DURING THERMAL DISPLACEMENT PROCESS IN POROUS MEDIA UNDER LOCAL THERMAL EQUILIBRIUM

NUMERICAL INVESTIGATION OF COUPLED ANOMALOUS DIFFUSION AND HEAT TRANSFER DURING THERMAL DISPLACEMENT PROCESS IN POROUS MEDIA UNDER LOCAL THERMAL EQUILIBRIUM

Stable and unstable miscible displacements in layered porous media

The effect of permeability heterogeneities and viscosity variations on miscible displacement processes in porous media is examined using high-resolution numerical simulations and reduced theoretical modelling. The planar injection of one fluid into a fluid-saturated, two-dimensional porous medium with a permeability that varies perpendicular to the flow direction is studied. Three cases are considered, in which the injected fluid is equally viscous, more viscous or less viscous than the ambient fluid. In general it is found that the flow in each case evolves through three regimes. At early times, the flow exhibits the concentration evolves diffusively, independent of both the permeability structure and the viscosity ratio. At intermediate times, the flow exhibits different dynamics including channelling and fingering, depending on whether the injected fluid is more or less viscous than the ambient fluid, and depending on the relative magnitude of the viscosity and permeability variations. Finally, at late times, the flow becomes independent of the viscosity ratio and dominated by shear-enhanced (Taylor) dispersion. For each of the regimes identified above, we develop reduced-order models for the evolution of the transversely averaged concentration and compare them to the full numerical simulations.

Experimental study on the inlet behavior of CO2 foam three phase displacement processes in porous media

In relation with the potential applications of CO2 foam technology on Enhanced Oil Recovery and CO2 geological storage, the foam assisted CO2 displacement process in a surfactant solution and oil pre-saturated porous medium is experimentally investigated with special attention on the dynamic foam propagation behavior in the entrance region of porous media. Computational Tomography (CT) imaging is employed to visualize the transient CO2 foam sweep process and the dual-energy CT measurement is performed to obtain the dynamic three phase saturation distributions along the sample core. Studying parameters include the comparison with N2 foam, system backpressure and the porous medium permeability. It is found foam could push most of the liquid phase in the latter part of the porous media but leaves the forepart of the sample less flooded, showing a clear entrance effect of foam flooding process. Compared to CO2 foam, N2 foam displacement process shows higher liquid phase saturation in the entrance section and presents less oil recovery rate. Elevating system backpressure to 1.0 MPa leads to less pressure drop for CO2 foam flooding process without compromising the oil phase sweep efficiency. The CO2 foam flooding process in lower permeable medium shows higher pressure drop and higher oil recovery rate. The mechanisms for the inlet behavior of the foam displacement processes have been scrutinized based on good qualitative and quantitative agreement of the experimental and numerical results with the stochastic bubble population balance model.

Effect of monovalent and divalent salts on the interfacial tension of pure hydrocarbon-brine systems relevant for low salinity water flooding

Interfacial tension between hydrocarbon liquids and salt water is a very important property for many industrial applications, especially in petroleum industry. Interfacial tension, in addition to other factors, has direct impact on displacement process in porous media so thus on oil recovery. Very recently, the salinity of injection brine has been regarded as a key factor in oil recovery using low salinity water flooding process. Decrease in the interfacial tension between crude oil and injection brine at low salinity condition might be a reason behind recovery improvement as suspected by some researchers; but there are also other effects associated with low salinity water flooding like wettability alteration, fine migration, mineral dissolution etc. It is suspected that the interaction of polar components at oil-water interface lead to the reduction of interfacial tension. However, the actual mechanism is not known and still under research. The main objective of this work is to determine the effect of salt concentration and type of ions present in an aqueous phase on the interfacial tension between pure hydrocarbon liquids and water. Different hydrocarbon liquids, such as aliphatic and aromatics, have been tested to understand the interaction of monovalent and divalent salts on the interfacial tension. The study reports the interfacial tension of five pure hydrocarbon liquids against solutions of three different salts (NaCl, MgCl2 and CaCl2) over a wide range of salinities. The interfacial tension measurements were done using Wilhelmy plate method by a dynamic contact angle tensiometer. All the experiments were conducted at room temperature and atmospheric pressure. The results lead us to the view that there is low a salinity concentration where the hydrocarbon/brine interfacial tension shows a minimum value. The type of salt also has a significant effect on interfacial tension of aliphatic and aromatic hydrocarbons. Monovalent salt found to be effective in reducing interfacial tension of aliphatic hydrocarbons while divalent salts were found to be effective for aromatic hydrocarbons. The possible mechanism for the reduction in IFT at low salt concentration has also been explained using Gibb's adsorption isotherm. In addition, the trend in IFT has been explained in the light of well-known Jones-Ray effect.

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.

Behavior of CO2/water flow in porous media for CO2 geological storage

A clear understanding of two-phase fluid flow properties in porous media is of importance to CO2 geological storage. The study visually measured the immiscible and miscible displacement of water by CO2 using MRI (magnetic resonance imaging), and investigated the factor influencing the displacement process in porous media which were filled with quartz glass beads. For immiscible displacement at slow flow rates, the MR signal intensity of images increased because of CO2 dissolution; before the dissolution phenomenon became inconspicuous at flow rate of 0.8mLmin−1. For miscible displacement, the MR signal intensity decreased gradually independent of flow rates, because supercritical CO2 and water became miscible in the beginning of CO2 injection. CO2 channeling or fingering phenomena were more obviously observed with lower permeable porous media. Capillary force decreases with increasing particle size, which would increase permeability and allow CO2 and water to invade into small pore spaces more easily. The study also showed CO2 flow patterns were dominated by dimensionless capillary number, changing from capillary finger to stable flow. The relative permeability curve was calculated using Brooks-Corey model, while the results showed the relative permeability of CO2 slightly decreases with the increase of capillary number.

A Review of Modeling Thermal Displacement Processes in Porous Media

The subject of heat transfer in oil reservoirs has gained huge attention, due to its diverse range of applications in petroleum reservoir management and thermal recovery for enhanced oil recovery. Thermal recovery methods entail the addition of heat energy into the reservoir through injection wells with the aim of reducing the in situ oil viscosity which is usually around several thousand centipoise cP (in S.I unit kg/m s) at reservoir conditions to very low values at steam temperatures. In addition, several other mechanisms are associated with thermal recovery methods. These include thermal expansion of oil, steam distillation, and relative permeability changes, which contribute to the ultimate recovery of the reservoir. In this article, a detailed review of non-isothermal modeling in an oil reservoir is presented. In addition, a few remarks regarding the momentum transport and the energy balance equations and its various modifications through the years are provided. Finally, a memory-based formulation is proposed to capture the alteration of rock and fluid properties with time as well as accounting for other phenomena not described by classic diffusion equations.

Numerical Modeling of Miscible Viscous Fingering Instabilities by High-Order Methods

In this paper, a high-order method is used to simulate the viscous fingering fluid instability during the miscible displacement process in porous media, on structured and unstructured grids. The numerical model incorporates decoupling in time, discontinuous Galerkin method of high order, flux reconstruction and parallel implicit solvers to produce an accurate and efficient predictive tool for finger growth. This paper shows that the proposed numerical approach is a competitive method to simulate several viscous fingering problems, such as rectilinear flow, density-driven flow and radial flow. The numerical model does not suffer from grid orientation, and accurately measures finger growth rate. Convergence of the fingering pattern is obtained under mesh refinement and increased polynomial degree.

Pore-scale simulation of miscible displacement in porous media using the lattice Boltzmann method

A numerical model based on the lattice Boltzmann method is presented to investigate the viscous fingering phenomena of miscible displacement processes in porous media, which involves the fluid flow, heat transfer and mass transport. Especially, temperature- and concentration-dependent pore-fluid viscosity is considered. A complete list is derived and given for the conversion of relevant physical variables to lattice units to facilitate the understanding and implementation of the coupled problems involving fluid flow, heat transfer and mass transport using the LBM. To demonstrate the proposed model capacity, two different complex geometry microstructures using high resolution micro-computed tomography (micro-CT) images of core sample have been obtained and incorporated as computation geometries for modeling miscible displacement processes in porous media. The viscous fingering phenomena of miscible displacement processes are simulated in two different cases, namely in a channel and a porous medium respectively. Some influencing factors on the miscible displacement process, such as the pore-scale microstructure, Le number and Re number, are studied in great detail. The related simulation results have demonstrated that: (1) the existence of the pore-scale microstructure can have a significant effect on the front morphologies and front propagation speed in the miscible displacement process; (2) as the Le number increases, the fluid front and thermal front evolve differently, with the thermal front being less unstable due to more diffusion; (3) a larger Re number can lead to an increase in the propagation speed of the front.