Immiscible Displacement Processes Research Articles

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.

Lattice Boltzmann simulation of immiscible displacement in the complex micro-channel

The immiscible displacement process in micro-channel, which widely existes in daily life and industrial production, is an important research subject. This subject is a typical contact line problem involving complicated fluid-fluid interactions and fluid-solid interactions which have attracted the interest of many scholars. Although the immiscible displacement in micro-channels has been studied by some researches, the problem is still not fully understood because the mechanism of the immiscible displacement is very complex. In order to further explain the physical mechanism of immiscible displacement process in micro-channels, detailed numerical simulations are carried out in a complex micro-channel containing a semicircular cavity and a semicircular by bulge using an improved pseudo-potential lattice Boltzmann method (LBM). This model overcomes the drawback of the dependence of the fluid properties on the grid size, which exists in the original pseudo-potential LBM. Initially, the cavity is filled with the liquid and the rest of the area is filled with its vapour. The semicircular bulge represents the roughness of the micro-channel. The approach is first validated by the Laplace law. The results show that the numerical results are in good agreement with the theoretical predictions. Then the model is employed to study the immiscible displacement process in the micro-channel. The effects of the surface wettability, the surface roughness, the viscosity ratio between the liquid phase and the gas phase, and the distance between the semicircular cavity and the semicircular bulge are studied. The simulation results show that the influence of the surface wettability on the displacement process is a decisive factor compared with other factors. With the increase of the contact angle, the displacement efficiency increases and the displacement time decreases. When the contact〉is larger than a certain value, all of the liquid can be displaced from the cavity. At that time, the displacement efficiency is equal to 1. The above results are consistent with the theoretical prediction that with the increase of the contact angle, the liquid is easily driven out of the cavity because the adhesion force of the liquid in the cavity decreases. On the other hand, the influence of the surface roughness on the displacement process is more complex. The displacement efficiency increases with the radius of the semicircle bulge increasing in a certain range. When the radius is larger than a certain value, the liquid cannot be ejected from the cavity due to the velocity around the cavity is too small. Furthermore, the liquid cannot be displaced from the cavity at a small viscosity ratio. As the viscosity ratio increases, the displacement efficiency increases and the displacement time decreases. As for the distance between the semicircular bulge and the semicircular cavity, it promotes the displacement process at an early stage. When the distance exceeds a certain value, it has little effect on the displacement process.

Numerical investigation of oscillatory multiphase flow in porous medium with chemically active skeleton

Self-oscillating mode of reaction front propagation in multiphase flow in the porous medium with chemically active skeleton is investigated numerically. The considered flow represents an immiscible displacement process, such that the displacing fluid and the skeleton of the porous medium have chemically active components which react with production of gaseous phase. The calculations have demonstrated strong influence of the reaction kinetics on stability of the reactive flow. The presence of a time delay between the change of concentration of the reactants and the change of the reaction rate is shown to stimulate transition of the reaction front propagation to the oscillatory mode.

Beyond Darcy's law: The role of phase topology and ganglion dynamics for two-fluid flow.

In multiphase flow in porous media the consistent pore to Darcy scale description of two-fluid flow processes has been a long-standing challenge. Immiscible displacement processes occur at the scale of individual pores. However, the larger scale behavior is described by phenomenological relationships such as relative permeability, which typically uses only fluid saturation as a state variable. As a consequence pore scale properties such as contact angle cannot be directly related to Darcy scale flow parameters. Advanced imaging and computational technologies are closing the gap between the pore and Darcy scale, supporting the development of new theory. We utilize fast x-ray microtomography to observe pore-scale two-fluid configurations during immiscible flow and initialize lattice Boltzmann simulations that demonstrate that the mobilization of disconnected nonwetting phase clusters can account for a significant fraction of the total flux. We show that fluid topology can undergo substantial changes during flow at constant saturation, which is one of the underlying causes of hysteretic behavior. Traditional assumptions about fluid configurations are therefore an oversimplification. Our results suggest that the role of fluid connectivity cannot be ignored for multiphase flow. On the Darcy scale, fluid topology and phase connectivity are accounted for by interfacial area and Euler characteristic as parameters that are missing from our current models.

Site‐Selective In Situ Grown Calcium Carbonate Micromodels with Tunable Geometry, Porosity, and Wettability

Micromodels with simplified porous microfluidic systems are widely used to mimic the underground oil‐reservoir environment for multiphase flow studies, enhanced oil recovery, and reservoir network mapping. However, previous micromodels cannot replicate the length scales and geochemistry of carbonate because of their material limitations. Here a simple method is introduced to create calcium carbonate (CaCO3) micromodels composed of in situ grown CaCO3. CaCO3 nanoparticles/polymer composite microstructures are built in microfluidic channels by photopatterning, and CaCO3 nanoparticles are selectively grown in situ from these microstructures by supplying Ca2+, CO32− ions rich, supersaturated solutions. This approach enables us to fabricate synthetic CaCO3 reservoir micromodels having dynamically tunable geometries with submicrometer pore‐length scales and controlled wettability. Using this new method, acid fracturing and an immiscible fluid displacement process are demonstrated used in real oil field applications to visualize pore‐scale fluid–carbonate interactions in real time.

Characterization of immiscible fluid displacement processes with various capillary numbers and viscosity ratios in 3D natural sandstone

To characterize the influence of reservoir conditions upon multiphase flow, we calculated fluid displacements (drainage processes) in 3D pore spaces of Berea sandstone using two-phase lattice Boltzmann (LB) simulations. The results of simulations under various conditions were used to classify the resulting two-phase flow behavior into three typical fluid displacement patterns on the diagram of capillary number (Ca) and viscosity ratio of the two fluids (M). In addition, the saturation of the nonwetting phase was calculated and mapped on the Ca–M diagram. We then characterized dynamic pore-filling events (i.e., Haines jumps) from the pressure variation of the nonwetting phase, and linked this behavior to the occurrence of capillary fingering. The results revealed the onset of capillary fingering in 3D natural rock at a higher Ca than in 2D homogeneous granular models, with the crossover region between typical displacement patterns broader than in the homogeneous granular model. Furthermore, saturation of the nonwetting phase mapped on the Ca–M diagram significantly depends on the rock models. These important differences between two-phase flow in 3D natural rock and in 2D homogeneous models could be due to the heterogeneity of pore geometry in the natural rock and differences in pore connectivity. By quantifying two-phase fluid behavior in the target reservoir rock under various conditions (e.g., saturation mapping on the Ca–M diagram), our approach could provide useful information for investigating suitable reservoir conditions for geo-fluid management (e.g., high CO2 saturation in CO2 storage).

Experimental analysis of spatial correlation effects on capillary trapping of supercritical CO2 at the intermediate laboratory scale in heterogeneous porous media

AbstractSeveral numerical studies have demonstrated that the heterogeneous nature of typical sedimentary formations can favorably dampen the accumulation of mobile CO2 phase underneath the caprock. Core flooding experiments have also shown that contrasts in capillary entry pressure can lead to buildup of nonwetting fluid phase (NWP) at interfaces between facies. Explicit representation of geological heterogeneity at the intermediate (cm‐to‐m) scale is a powerful approach to identify the key mechanisms that control multiphase flow dynamics in porous media. The ability to carefully control flow regime and permeability contrast at a scale that is relevant to CO2 plume dynamics in saline formations offers valuable information to understand immiscible displacement processes and provides a benchmark for mathematical models. To provide insight into the impact of capillary heterogeneity on flow dynamics and trapping efficiency of supercritical CO2 under successive drainage and imbibition conditions, we present an experimental investigation conducted in a synthetic sand reservoir. By mimicking the interplay of governing forces at reservoir conditions via application of surrogate fluids, we performed three immiscible displacement experiments to observe the entrapment of NWP in heterogeneous porous media. Capillary trapping performance is evaluated for each scenario through spatial and temporal variations of NWP saturation; for this reason we adopted X‐ray attenuation to precisely measure phase saturation throughout the flow domain and apply spatial moment analysis. The sweeping performance of two different permeability fields with comparable variance but distinct spatial correlation was compared against a homogeneous base case with equivalent mean permeability by means of spatial moment analysis.

Numerical simulation of displacement characteristics of CO2 injected in pore-scale porous media

Pore structure of porous media, including pore size and topology, is rather complex. In immiscible two-phase displacement process, the capillary force affected by pore size dominates the two-phase flow in the porous media, affecting displacement results. Direct observation of the flow patterns in the porous media is difficult, and therefore knowledge about the two-phase displacement flow is insufficient. In this paper, a two-dimensional (2D) pore structure was extracted from a sandstone sample, and the flow process that CO2 displaces resident brine in the extracted pore structure was simulated using the Navier–Stokes equation combined with the conservative level set method. The simulation results reveal that the pore throat is a crucial factor for determining CO2 displacement process in the porous media. The two-phase meniscuses in each pore throat were in a self-adjusting process. In the displacement process, CO2 preferentially broke through the maximum pore throat. Before breaking through the maximum pore throat, the pressure of CO2 continually increased, and the curvature and position of two-phase interfaces in the other pore throats adjusted accordingly. Once the maximum pore throat was broken through by the CO2, the capillary force in the other pore throats released accordingly; subsequently, the interfaces withdrew under the effect of capillary fore, preparing for breaking through the next pore throat. Therefore, the two-phase displacement in CO2 injection is accompanied by the breaking through and adjusting of the two-phase interfaces.

Two dimensional pore network modelling and simulation of non-isothermal drying by the inclusion of viscous effects

Drying as an immiscible displacement process has a great importance in chemical industries. The efficiency of the process is highly affected by the pore space structure of the solids. In this study non-isothermal drying behaviour of capillary porous media is studied in two dimensional (2D) mono-modal and bi-modal pore network models. Non-isothermal drying in the absence of viscous force has been studied previously. The presented model includes viscous flow in liquid phase while capillary pumping in liquid phase and diffusion in gas phase are the other mass transfer mechanisms at the pore scale. Conduction is considered as the heat transfer mechanism. The effect of viscous flow and temperature of drying air are studied. The simulation results are compared with a non-viscous model. The results indicate that the effect of viscous force is more significant in low temperatures. During the first falling drying rate period viscous forces dominate capillary pumping and decrease drying rate. The first drying rate period is not affected by viscous forces; however, the morphology of the pore space is an important parameter in forming this period. In bi-modal pore network, drying rate is higher due to the suitable arrangement of macro and microthroats in its structure.

An Estimation of Wave Attenuation Factor in Ultrasonic Assisted Gravity Drainage Process

It has been proved that ultrasonic energy can considerably increase the amount of oil recovery in an immiscible displacement process. Although many studies have been performed on investigating the roles of ultrasonic waves, based on the best of our knowledge, little attention has been paid to evaluate wave attenuation parameter, which is an important parameter in the determination of the energy delivered to the porous medium. In this study, free fall gravity drainage process is investigated in a glass bead porous medium. Kerosene and Dorud crude oil are used as the wetting phases and air is used as the non-wetting phase. A piston-like displacement model with considering constant capillary pressure and applying Corey type approximation for relative permeabilities of both wetting and nonwetting phases is applied. A pressure term is considered to describe the presence of ultrasonic waves and the attenuation factor of ultrasonic waves is calculated by evaluating the value of external pressure applied to enhance the flow using the history matching of the data in the presence and absence of ultrasonic waves. The results introduce the attenuation factor as an important parameter in the process of ultrasonic assisted gravity drainage. The results show that only a low percentage of the ultrasonic energy (5.8% for Dorud crude oil and 3.3% for kerosene) is delivered to the flow of the fluid; however, a high increase in oil recovery enhancement (15% for Dorud crude oil and 12% for Kerosene) is observed in the experiments. This proves that the ultrasonic waves, even when the contribution is not substantial, can be a significantly efficient method for flow enhancement.

Effects of capillary pressure – fluid saturation – relative permeability relationships on predicting carbon dioxide migration during injection into saline aquifers

Abstract Mathematical modeling and numerical simulations on carbon dioxide plume migration in confined saline aquifers have become important approaches to evaluate storage capacity and efficiency for carbon dioxide sequestration and to predict potential risks of leakage during and after carbon dioxide injection into subsurface formations. The effects of the characteristic functions relating capillary pressures and relative permeabilities to fluid saturations are critical in predicting carbon dioxide plume migration in saline aquifers. In this paper, four well known models, i.e. Brooks-Corey-Burdine model (BCB), Brooks-Corey- Mualem model (BCM), Van Genuchten-Burdine model (VGB), and Van Genuchten-Mualem model (VGM), were incorporated with an immiscible displacement process model to simulate carbon dioxide injection into saline aquifers. Parametric analysis was conducted to identify the influences of parameters in the Brooks-Corey based model on the predictions of carbon dioxide plume migration in a confined saline aquifer. A comprehensive comparison was carried out to reveal the different performances of the models with respect to the evolutions and patterns of carbon dioxide plume in the confined saline aquifer. The simulation results indicate that the saturation distributions of carbon dioxide are drastically sensitive to the capillary entry pressure. However, the parameters and in the Brooks-Corey based model, which are related to pore size distribution and tortuosity ratio of a porous medium, respectively, have little effects on predicting carbon dioxide plume migration in the saline aquifer. Moreover, different models may cause extensive influences on the carbon dioxide distributions at the region that is close to the injection well and at the leading edges of carbon dioxide plume in the saline aquifer. Hence, the results indicate that for the evaluation of the storage capacity and efficiency of a saline aquifer to trap carbon dioxide, the storage capacity of the saline aquifer could be over- estimated by using the BCB model, whereas it could be underestimated by using the VGM model. On the other hand, for evaluations of potential leakage of carbon dioxide in saline aquifers, where the movement of the leading edge of carbon dioxide plume is monitored, the VGM model is a safe choice in simulations. These results have potentially significant implications for estimation of carbon dioxide storage capacity of saline aquifers and assessments on potential risks of leakage.

Case study of using boundary integration technique in reservoir modeling of single- and two-phase immiscible fluid flow

Abstract Petroleum reservoir simulation is a process of modeling the complex physical phenomena inside a reservoir. The goal is to determine how hydrocarbons and water behave and how local reservoir characteristics affect the oil and gas recovery in the reservoir. This study presents an application of two rigorous analytical based numerical schemes in petroleum engineering, so called the Boundary Element Method (BEM) and its hybrid form, the Dual Reciprocity Boundary Element Method (DRBEM). They are proven to be able to provide a computationally efficient means of handling single- and multi-phase flow in a homogeneous medium through the comparison with results obtained by COMSOL. The accuracy can be further enhanced by incorporating singularity programming and Laplace transformation techniques; hence an alleviation of numerical errors caused by singularities and a time derivative is achieved. It is observed that these two methods can be an alternative tool to analyze pressure transient performance in both single- and multi-phase flow, and estimate the saturation change during an immiscible displacement process. In addition, it has been shown that there are numerous potential areas of oil recovery where COMSOL can be a useful and successful means of research and design advancement.

A Model with Back-Propagation Algorithm for Recovery Efficiency Forecast of Carbon Dioxide Flooding

As one of the most important displacements in producing petroleum, CO2 flooding has been developed for nearly 50 years around the world in order to improve the tertiary recovery. The recovery efficiency, R, is a key parameter in the CO2 displacement of crude oil. Traditionally, R is determined by conducting CO2 flooding experiment, requiring considerable resources and long time periods, with the consequence of a limited number of core plug evaluations for a particular reservoir. Thus, the estimation of R with mathematical models is developed in recent years, which also needs plenty of relevant parameters considered. The study reported in this paper uses artificial neural network to determine R. Five dimensionless variables are considered to analyse the CO2 immiscible displacement process. An optimal model is chosen with its suitable hidden layer nodes and activation functions for the hidden and output layers. Its performance is compared with the numerical simulation model, demonstrating the superior performance of the proposed R prediction model.

An experimental study on CO2/water displacement in porous media using high-resolution Magnetic Resonance Imaging

CO2/water displacement process in porous media under sequestration conditions was observed using high-resolution Magnetic Resonance Imaging (MRI) technique. The porous media was a packed bed filled with glass beads. Fast spin echo multi slice sequence (FSEM) was used to measure the distribution of CO2 and water in the porous media. For immiscible displacement experiments, three stages were obtained from the MR signal intensity profile. The CO2 channeling or fingering phenomena was obviously for the difference of permeability during the second stage. The final water residual saturation depended on permeability, and lower permeability always leads to larger final saturation. For miscible displacement, the displacement process was also divided into three stages from MR signal intensity profile. The MR signal intensity decreased gradually for the resolving of CO2 into water in the first stage. A piston-like miscible front moved uniformly from the top to the bottom of the FOV (field of view) during the second stage, and the MR signal intensity decreased sharply. The displacement efficiency in miscible displacement is larger than that in immiscible displacement process. It is clear that water displacement efficiency or average CO2 saturation depends on flow rate. With the CO2 flow rate increasing, the relatively uniform CO2 distribution and the uniform CO2 front occurred. Additionally, final water saturation decreased. With the core analysis methods, the CO2 velocities were obtained, which were applied to evaluate the capillary dispersion rate, viscous dominated fraction flow and gravity flow function. The capillary dispersion rate donated the effects of capillary, which was largest at water saturations of 0.6 and 0.7. At a high flow rate, the viscous force was dominated over the porous media. When at a low flow rate, the gravity force became important and played a positive role in downward displacements.

Immiscible Displacement of a Wetting Fluid by a Non-wetting One at High Capillary Number in a Micro-model Containing a Single Fracture

Most reservoirs in Iran are heterogeneous fractured carbonate reservoirs. Heterogeneity causes an earlier breakthrough and an unstable front which leads to a lower recovery. A series of experiments were conducted whereby the distilled water displaced n-Decane in strongly oil-wet glass micro-models containing a single fracture. Experimental data from image analysis of immiscible displacement processes are used to modify the Buckley–Leverett and fractional flow equations by a heterogeneity factor. It is shown that the heterogeneity factor in the modified equations can be expressed as a function of fracture length and orientation.

The Effect of Fracture Geometrics on Breakthrough Time in the Immiscible Displacement Process Through Strongly Oil Wet Fractured Porous Media: Experimental Investigation

The immiscible process appears to be one of the first feasible methods for the extraction of oil reserves. However, there is a lack of fundamental understanding of how fracture geometrical characteristics control the efficiency of oil recovery in this type of enhanced oil recovery technique. In this article, a series of experiments were conducted whereby the distilled water displaced n-decane in strongly oil wet glass micro-models having different fracture geometries. Breakthrough time, as a function of injected pore volume of distilled water, was measured using image analysis of the provided pictures. It has been observed that when the fractures' length is increased, the breakthrough time is decreased. In contrast, when the orientation angle related to flow direction is increased, breakthrough time is increased. A correlation for linear flow in fractured media is generated, which represents the breakthrough time as a function of fracture length and its orientation. This correlation is validated by immiscible displacement tests on other fractured micro-models in which fracture geometrics were designed randomly.

A Simplified Model and Similarity Solutions for Interfacial Evolution of Two-Phase Flow in Porous Media

For two-phase flows of immiscible displacement processes in porous media, we proposed a simplified model to capture the interfacial fronts, which is given by explicit expressions and satisfies the continuity conditions of pressure and normal velocity across the interface. A new similarity solution for the interfacial evolution in the rectangular coordinate system was derived by postulating a first-order approximation of the velocity distribution in the region that the two-phase fluids co-exist. The interfacial evolution equation can be explicitly expressed as a linear function, where the slope of the interfacial equation is simply related to the mobility ratio of two-phase fluids in porous media. The application of the proposed solutions to predictions of interfacial evolutions in carbon dioxide injected into saline aquifers was illustrated under different mobility ratios and operational parameters. For the purpose of comparison, the numerical solutions obtained by level set method and the similarity solutions based on the Dupuit assumptions were presented. The results show that the proposed solution can give a better approximation of interfacial evolution than the currently available similarity solutions, especially in the situation that the mobility ratio is large. The proposed approximate solutions can provide physical insight into the interfacial phenomenon and be readily used for rapidly screening carbon dioxide storage capacity in subsurface formations and monitoring the migration of carbon dioxide plume.

A Simulation Study of Carbon Dioxide Sequestration in a Depleted Oil Reservoir

Oil fields offer significant potential for storing carbon dioxide (CO2) and will most likely be the first large-scale geological targets for sequestration because the infrastructure, experience, and permitting procedures already exist. In addition, almost 40 years' experience in enhanced oil recovery (EOR) allows utilization of carbon capture and storage (CCS) and CO2 sequestration techniques in such a way as to improve recovery of petroleum fields and reduce the environmental issue of fossil fuel combustion gas products, particularly carbon dioxide. Carbon dioxide is one of the main greenhouse gases that causes global warming. As a response to global warming, geologic sequestration of CO2 in oil and gas reservoirs is one possibility to reduce the amount of CO2 released to the atmosphere. This simulation study presents a synthetic geologic model that is used to sequestrate carbon dioxide beside an EOR immiscible displacement process.

Influence of Viscous and Capillary Forces on Immiscible Fluid Displacement: Pore-Scale Experimental Study in a Water-Wet Micromodel Demonstrating Viscous and Capillary Fingering

Unstable immiscible fluid displacement in porous media affects geological carbon sequestration, enhanced oil recovery, and groundwater contamination by non-aqueous phase liquids. Characterization of immiscible displacement processes at the pore scale is important to better understand macroscopic processes at the continuum scale. A series of displacement experiments was conducted to investigate the impacts of viscous and capillary forces on displacement stability and fluid saturation distributions in a homogeneous water-wet pore network micromodel with precisely microfabricated pore structures. Displacements were studied using seven wetting–non-wetting fluid pairs with viscosity ratios M (viscosity of the advancing non-wetting fluid divided by the viscosity of the displaced wetting fluid) ranging 4 orders of magnitude from log M = −1.95 to 1.88. The micromodel was initially saturated with either polyethylene glycol 200 (PEG200) or water as the wetting fluid, which was then displaced by a non-wetting alkane...

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

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