Browsing by Subject "Porous media"

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Artificial Leaf for Biofuel Production and Harvesting: Transport Phenomena and Energy Conversion
(2013-08) Murphy, Thomas Eugene; Berberoglu, Halil
Microalgae cultivation has received much research attention in recent decades due to its high photosynthetic productivity and ability to produce biofuel feedstocks as well as high value compounds for the health food, cosmetics, and agriculture markets. Microalgae are conventionally grown in open pond raceways or closed photobioreactors. Due to the high water contents of these cultivation systems, they require large energy inputs for pumping and mixing the dilute culture, as well as concentrating and dewatering the resultant biomass. The energy required to operate these systems is generally greater than the energy contained in the resultant biomass, which precludes their use in sustainable biofuel production. To address this challenge, we designed a novel photobioreactor inspired by higher plants. In this synthetic leaf system, a modified transpiration mechanism is used which delivers water and nutrients to photosynthetic cells that grow as a biofilm on a porous, wicking substrate. Nutrient medium flow through the reactor is driven by evaporation, thereby eliminating the need for a pump. This dissertation outlines the design, construction, operation, and modeling of such a synthetic leaf system for energy positive biofuel production. First, a scaled down synthetic leaf reactor was operated alongside a conventional stirred tank photobioreactor. It was demonstrated that the synthetic leaf system required only 4% the working water volume as the conventional reactor, and showed growth rates as high as four times that of the conventional reactor. However, inefficiencies in the synthetic leaf system were identified and attributed to light and nutrient limitation of growth in the biofilm. To address these issues, a modeling study was performed with the aim of balancing the fluxes of photons and nutrients in the synthetic leaf environment. The vascular nutrient medium transport system was also modeled, enabling calculation of nutrient delivery rates as a function of environmental parameters and material properties of the porous membrane. These models were validated using an experimental setup in which the nutrient delivery rate, growth rate, and photosynthetic yield were measured for single synthetic leaves. The synthetic leaf system was shown to be competitive with existing technologies in terms of biomass productivity, while requiring zero energy for nutrient and gas delivery to the microorganisms. Future studies should focus on utilizing the synthetic leaf system for passive harvesting of secreted products in addition to passive nutrient delivery.
Construction and validation of microfluidic platforms for investigation of multiphase flow and nanofluids in porous media
(2018-06-27) Xu, Ke, Ph. D.; Balhoff, Matthew T.; Huh, Chun; Mohanty, Kishore K; Bonnecaze, Roger T; Daigle, Hugh
Flow and transport in porous media is the fundamental physical process in many important applications such as hydrocarbon recovery, carbon dioxide subsurface sequestration, treatment of non-aqueous liquid pollutions in soil systems, and flooding control for fuel cell systems. Clear description, correct modeling and precise prediction of flow in porous media are of great significance. Although many single-phase and multiphase systems can be characterized using macroscopic models such as Darcy’s law (or the multiphase form of it), other complex flow systems, such as emulsion flow, nanoparticle suspension flow, etc., require a more detailed description. For those complex cases, revealing the pore-scale physics is necessary for larger-scale modeling and predictions. Microfluidics provide a simple way to visualize micron-scale flow behavior with excellent controllability, thus helping to clarify the fundamental pore-scale flow mechanisms and is, therefore, useful for studying flow and transport in porous media. In this work, several special micromodel designs from the single-pore level to pore-network level on microchips were made in order to capture realistic pore-scale flow mechanisms while keeping the system simplified enough for easy quantification. At the single-pore level, the trapping and mobilization of a non-wetting oil droplet at a pore-throat structure are investigated on an ideal pore-throat microfluidic geometry. A simple physical model is derived and the effects of bare nanoparticle aqueous suspension in mobilizing oil is further studied. A dual-permeability microchannel is used to study the emulsion flow in natural fracture system and a synergistic effect between nanoparticles and non-ionic surfactant is investigated to stabilize the emulsion and to potentially improve sweep efficiency. At the pore-network-pore level, a 2.5-D porous micromodel is fabricated to introduce essential 3-D feature in traditional 2-D porous micromodel. On this advanced 2.5-D micromodel, multiple complex fluid systems, including spontaneous imbibition, unstable water drainage, ultra-low IFT flooding, bubble evolution under Ostwald ripening, nanofluid flooding, etc., have been studied, with new physics revealed and modeled. A novel EOR method using nanoparticle treated oil (NPTO) is proposed and validated.
Determination of Field Scale Dispersivities by Mathematical Modeling
(1981-08) Ravnaas, Robert Dean; Lake, Larry
Dispersion in heterogeneous porous media results from the simultaneous action of a mechanical phenomenon and molecular diffusion. The mechanical contribution ari-ses from discrepancies in flow streamlines caused by inhomogeneities within the system. A two dimensional computer simulator based upon the moving point method was written. This method accura-tely described all levels of numerical dispersion. Observation well data from the El Dorado field in Kansas were effluent history matched with corresponding simulator runs. Longitudinal dispersivities ranged from 12 ft to 20 ft while transverse dispersivities ranged from o.oo ft to 0.06 ft. An "ideal" sampling scheme is pro-posed for future field wide dispersion tests, enabling more accurate determinations of history matched disper-sivities. The Lake and Hirasaki method of grouping layered systems producing effective one-dimensional disper-sivities, was found to be a relatively quick, approximate, procedure. This method takes into account the oftentimes important relative spatial ordering of reservoir layers.
Effect of Structure on Petrophysical Properties of Porous Media
(1994-05) Gao, Yaming; Sharma, Mukul Mani
The objective of this project is to relate the microscopic structure of porous media to macroscopic properties, such as porosity, permeability, dispersion coefficient, and chemical reactivity. In the first part of this study, fluid flow in porous media is simulated by a lattice gas automaton model. The fluid velocity profiles and pressure drops around obstacles of known-shape are calculated. Heterogeneous permeability fields at a macroscopic and megascopic length scale are created by distributing scatterers within the fluid flow field. These scatterers act as obstacles to flow. The loss in momentum of the fluid is directly related to the permeability of the lattice gas model. It is shown that by varying the probability of occurrence of solid nodes, the permeability of the porous medium can be changed over several orders of magnitude. To simulate fluid flow in heterogeneous permeability fields, isotropic, anisotropic, random, and correlated permeability fields are generated. The lattice gas model developed here is used to obtain the effective permeability as well as the local fluid flow field. The method presented here can be used to simulate fluid flow in arbitrarily complex, heterogeneous porous media. The lattice gas automaton model is also applied to the problem of simulating dispersion and mixing in heterogeneous porous media. We demonstrate here that tracer concentration profiles and longitudinal dispersion coefficients can be computed for heterogeneous porous media It is shown that some basic petrographic measurements such as pore perimeter, pore size, and grain surface area can be made from thin sections that can be used to obtain an order of magnitude estimate of flow properties, such as permeability. The reactivity of rock with acid in an acidizing process depends on the geometrical arrangement of various minerals with respect to each other. A model is developed where the minerals are located in accordance with thin section images. Since the rate of reaction of each mineral is known, an erosion process is used to obtain the reactivity of the rock as a function of time. It is shown that this model provides substantially different results than a simple model that is based only on the mineral abundance in the rock matrix. This result can have a significant impact on currently used acidizing simulators.
The Effects of Capillary Pressure on Displacements in Stratified Porous Media
(1980-12) Yokoyama, Yoshio; Lake, Larry W.
The purpose of this study is to obtain a better understanding of capillary pressure effects on fluid dis-placement in stratified porous media. We do this by pre-senting and validating dimensionless scaling parameters which will assist in the evaluation of these effects. The interpretation of flow perpendicular to strati-fied layers is important because it is one of the greatest causes of mixing, thus, determining the longitudinal satura-tion profile. In stratified layers with large permeability contrast, the transverse flow (crossflow) due to capillary imbibition retards the fronts in higher permeability layers and advances the fronts in lower permeability layers. Conse-quently greater oil recovery results when compared to a no-crossflow case. In this study, emphasis was placed on the analysis of transverse capillary crossflow effects. First, a semi-implicit two-phase, two-dimensional, incompressible fluid simulation model is developed by a finite difference method. A three-point weighting scheme is incorporated to reduce numerical dispersion (truncation error) in a routine of inter-block transmissibility evaluation. Next five dimensionless parameters are introduced to correlate the porous medium's heterogeneity with mixing caused by capillary crossflow. Those are the dimensionless time (t0), the transverse capillary number (NCT), the longi-tudinal capillary number (NCL) , the heterogeneity function (R¢K) and the Leverett j-function. Finally the dimensional analysis is verified through computer simulation of two-layered porous media models, and several dimensionless correlation graphs are drawn. The study provides a basis for analyzing displace-ment behavior in stratified media and also suggests the same analysis can be extended to more complicated media.
Experimental analysis of electrostatic and hydrodynamic forces affecting nanoparticle retention in porous media
(2012-05) Murphy, Michael Joseph, 1986-; Bryant, Steven L.; Huh, Chun
There have been significant advances in the research of nanoparticle technologies for formation evaluation and reservoir engineering operations. The target applications require a variety of different retention characteristics ranging from nanoparticles that adsorb near the wellbore to nanoparticles that can travel significant distances within the porous medium with little or no retention on the grain substrate. A detailed understanding of the underlying mechanisms that cause nanoparticle retention is necessary to design these applications. In this thesis, experiments were conducted to quantify nanoparticle retention in unconsolidated columns packed with crushed Boise sandstone and kaolinite clay. Experimental parameters such as flow rate, injected concentration and sandpack composition were varied in a controlled fashion to test hypotheses concerning retention mechanisms and enable development and validation of a mathematical model of nanoparticle transport. Results indicate nanoparticle retention, defined as the concentration of nanoparticles remaining attached to grains in the porous medium after a volume of nanoparticle dispersion is injected through the medium and then displaced with brine, is a function of injected fluid velocity with higher injected velocities leading to lower retention. In many cases nanoparticle retention increased nonlinearly with increasing concentration of nanoparticles in the injected dispersion. Nanoparticle retention concentration was found to exhibit an upper bound beyond which no further adsorption from the nanoparticle dispersion to the grain substrate occurred. Kaolinite clay was shown to exhibit lower retention concentration [mg/m2] than Boise sandstone suggesting DLVO interactions do not significantly influence nanoparticle retention in high salinity dynamic flow environments.
Experimental Determination and Theoretical Prediction of Effective Thermal Conductivity of Porous Media
(1993-05) Mohanty, Sitakanta; Miller, Mark A.; Sharma, Mukul Mani
The objectives of this study are two-fold: a) to develop an experimental method for the accurate determination of thermal conductivity of fluid saturated porous media and b) to predict the experimental results through microscopic scale modeling. A steady-state apparatus has been designed, tested, and implemented for obtaining thermal conductivity with improved accuracy by minimizing heat losses. The apparatus is capable of measuring thermal conductivity at various fluid saturation conditions. The steady-state apparatus has also been modified for transient measurements to obtain thermal diffusivity. The thermal conductivity of the consolidated rocks show strong sensitivity to the type of saturating fluid. An attempt has been taken to construct a 3-D numerical model of a porous medium based on available 2-D information such as a thin-section by using indicator simulation algorithm. Results from this study indicates that the consolidated porous media is too complex to be represented by a few statistics. A recursive model based on the concept of real space renormalization group has been developed to predict macroscopic properties by using the parameters characterizing the microscopic details. The macroscopic thermal conductivity was found to be relatively insensitive to the heterogeneity in the isotropically correlated systems even at large conductivity ratios of the individual components. The macroscopic thermal conductivity is a strong function of the aspect ratio describing heterogeneity in the anisotropically correlated systems even at small conductivity ratios of the components. A random walk model has been developed to calculate conductivity of extremely large systems with small correlation structures and with any number of components. A qualitative study on the effect of multiphase fluid saturation on the effective thermal conductivity has been conducted by using a thin section. Multiphase fluid saturation has been numerically generated by using Monte Carlo annealing algorithm. The effect of fluid saturation is not monotonic as has been commonly believed so far. Comparison between experimental results and the results from the numerical studies using spherepacks revealed that convective heat transfer may be a much stronger problem in experimental methods than ordinarily believed.
Experimental study of convective dissolution of carbon dioxide in porous media
(2014-12) Liang, Yu, active 21st century; DiCarlo, David Anthony, 1969-
Geological carbon dioxide (CO₂) capture and storage in geological formations has the potential to reduce anthropogenic emissions. The viability of technology depends on the long-term security of the geological CO₂ storage. Dissolution of CO₂ into the brine, resulting in stable stratification, has been identified as the key to long-term storage security. The dissolution rate determined by convection in the brine is driven by the increase of brine density with CO₂ saturation. Here we present a new analog laboratory experiment system to characterize convective dissolution in homogeneous porous medium. By understanding the relationship between dissolution and the Rayleigh number in homogeneous porous media, we can evaluate if convective dissolution occurs in the field and, in turn, to estimate the security of geological CO₂ storage fields. The large experimental assembly will allow us to quantify the relationship between convective dynamics and the Rayleigh number of the system, which could be essential to trapping process at Bravo Dome. A series of pictures with high resolution are taken to show the existence and movement of fingers of analog fluid. Also, these pictures are processed, clearly showed the concentration of analog fluid, which is essential to analyze the convective dissolution in detail. We measured the reduction in the convective flux due to hydraulic dispersion effect compared to that in homogeneous media, to determine if convective dissolution is an important trapping process at Bravo Dome.
Finite Element Formulations for Moving Boundaries, Material Interfaces, and Postprocessing, With Applications to Heat Transfer and Consolidation in Porous Media
(1988-05) MacKinnon, Robert James; Carey, Graham F.; Sepehrnoori, Kamy
The research described here concerns finite element modeling of problems involving moving boundaries and different material types, together with postprocessing and superconvergence behavior. An example from geomechanics corresponding to underground coal gasification is included to demonstrate the moving grid and moving boundary technique. A new treatment for material interface elements is introduced as part of this formulation. In test calculations this treatment is shown to be superior to previous material averaging strategies. The postprocessing analysis and superconvergence theory is based on an entirely new approach which extensively uses Taylor series analysis and leads to some novel results in finite element modeling. These include new flux and stress postprocessing formulas, and new solution enhancement strategies. Some of these ideas are promising for treatment of other classes of problems such as those in reservoir engineering involving different material types and multiphase flow.
Flow of Dilute Oil-In-Water Emulsions in Porous Media
(1999-12) Mendez, Zuleyka Del Carmen; Sharma, Mukul Mani
The flow of dilute oil-in-water emulsions is of critical concern in produced water reinjection. Oil droplets and solids suspended in produced water are often hard to remove and are, therefore, reinjected into subsurface formations. A rapid injectivity decline in such water injection wells is commonly encountered. Eventually, these wells may have to be operated above the fracture gradient. The flow of emulsions in porous media determines the performance and lifetime of such water injection wells. Flow of dilute oil-in-water emulsions in porous media may also be encountered during enhanced oil recovery and stimulation operations. This dissertation is aimed at investigating the mechanisms of permeability impairment caused by the flow of dilute oil-in-water emulsions in cores containing residual oil. The study has both experimental and modeling components. The experimental program consisted of injecting well-characterized oil-in-water emulsions into cores containing a residual oil saturation. The permeability of different sections of the core as well as the droplet concentration and size distribution were measured as a function of time and position. Two crude oils, one from Prudhoe Bay and another from the North Sea (Brent crude oil) were used in core tests. Berea sandstone and Aloxite cores were used as porous media. Experimental results indicated that the presence of residual oil had a profound effect on the measured permeability decline. Droplets were generated from the residual oil present at pore throats after a critical capillary number is exceeded. It was found that high injection rates and low permeabilities enhance droplet formation. The generation of droplets is a primary contributing factor to the permeability reduction observed in different sections in the core. The permeability of the core, the droplet concentrations, the concentration of emulsifier present, the flow rate, and the properties of the crude oil all play important roles in determining the extent and rate of permeability impairment. High pressure gradient, high flow rate, low permeabilities, high oil concentrations and large droplet sizes contribute to a more rapid decline in permeability. It was observed that the permeability decline occurs in two stages, one associated with the injected droplets followed by a second stage during which generation of droplets plays an important role. After the onset of droplet generation, permeability decline is faster and more severe. This stage is evidenced by a high droplet concentration, in excess of the injected droplet concentration.
Foam flow in rough fractures at elevated temperatures and pressures
(2023-08) Radhakrishnan, Anuradha; Prodanovic, Masa; DiCarlo, David Anthony, 1969-; Johnston, Keith; Daigle, Hugh; Mohanty, Kishore
The flow of foam in fractures has diverse applications, ranging from the oil and gas industry to carbon capture and geothermal systems. This dissertation thoroughly examines the impact of fracture roughness, foam formulations, foam qualities, mineralogy, and elevated temperature (38°C to 150°C) and elevated pressures (1200 psi) on foam performance in fractures. Fractured core flood experiments are conducted to measure the apparent viscosity of foam and investigate the influence of fracture surface roughness on foam structure and stability. Throughout the studies, supercritical CO₂-based foams are employed. The research also aims to determine whether foam behavior inside a rough fracture resembles that of bulk foam or porous media foam. Fracture roughness is characterized using CT scans, and the stability of foam under high temperature and pressure conditions is explored. Furthermore, the ability of foam to suspend proppant particles and its interaction with various rock mineralogy, including sandstones, limestones, shales, and granites, are investigated, leading to interesting insights. The key findings reveal that foam flowing through rough fractures exhibits continuous regeneration and greater stability compared to foam in smooth fractures, irrespective of the rock mineralogy. Rough surfaces within fractures play a crucial role in enhancing foam stability, promoting lamella regeneration, enabling foam resistance against extreme temperatures and pressures. Micro-CT scans confirm the existence of varying aperture sizes along fracture walls, indicating the effectiveness of rough surfaces in facilitating foam flow. In rough fractures, bubbles near the surface form a structure characterized by a single lamella spanning the pore space, while the presence of asperities results in varying bubble sizes, introducing heterogeneity within the foam structure. Conversely, in smoother fractures, foam displays a bulk structure with smaller, uniform bubbles. The effectiveness of CO₂ foam in suspending proppant particles and its interaction with shale are demonstrated, with the foam exhibiting water absorption near shale particles, leading to higher foam quality in the vicinity of these particles. This interaction contributes to the maintenance of a stable foams. By studying foam behavior in fractures and optimizing foam formulations, we can unlock the full potential of foams across various industries, contributing to sustainable and efficient processes.
High-Resolution Methods for Enhanced Oil Recovery Simulation
(1993-08) Liu, Jianchun; Sepehrnoori, Kamy; Pope, Gary A.
Enhanced oil recovery processes involve multicomponent, multiphase flow through porous media. Proper numerical modeling and flow prediction are essential for the successful design and evaluation of these processes. Conventional simulation techniques suffer from either excessive artificial diffusion effects or highly spurious oscillations when modeling convection-dominated processes. These artificial effects can lead to a breakdown in the stability of the finite-difference scheme and to inaccurate predictions and erroneous conclusions. In this research we present high-resolution simulation techniques to overcome these problems and to improve the performance of numerical compositional reservoir simulators. We have applied a second-order time-correction method to a explicit scheme with high-order spatial discretization to increase its temporal accuracy and to stabilize the scheme by relaxing the Courant number limits at high cell Peclet numbers. The stability conditions of the Courant number limits as functions of cell Peeler numbers are presented. We use a third-order scheme to approximate the convection term and the Crank-Nicolson scheme to approximate the temporal derivative. The conditions sufficient for a finite-difference scheme to be total variation diminishing (TVD) are derived in a more general form which includes both the implicit and explicit differencing terms. Applying these conditions, we obtain the TVD constraints for both the implicit and explicit flux functions. These constraints form a TVD region which is a function of timestep size. Larger timestep sizes correspond to smaller TVD regions. Under the TVD constraints, the third-order TVD flux limiter is constructed using the third-order flux function to achieve higher accuracy. Accuracy is maintained with nonuniform grids. We have implemented the high-resolution techniques into the IMPES compositional simulators and developed a fully implicit simulator with the high-resolution numerical features. TVD constraints are applied to the species fluxes and the phase fluxes by imposing the TVD third-order limiter functions to the approximations of interface convections and interface relative permeabilities. For the IMPES formulation, the second-order time-correction terms are added to the dispersion coefficients. For the fully implicit formulation, the resulting nonlinear system of residual equations is solved for the primary variables. The flux limiter functions and their derivatives are updated at the end of each iteration. The simulation results show remarkable success in eliminating numerical effects and in resolving shock fronts, even for very highly convection-dominated problems. The high-resolution techniques use several hundred times less computing time to achieve the accuracy obtained using conventional techniques with finer grids. A fully implicit simulator using the high-resolution scheme produces more accurate results than one using conventional techniques and more stable results than the IMPES simulator. The performance of the simulator is greatly improved using suitable timestepping algorithms and efficient solution solvers.
Mechanistic study of menisci motion within homogeneously and heterogeneously wet porous media
(2009-08) Motealleh, Siyavash; Bryant, Steven L.
Oil reservoirs and soil can be homogeneously wet (water-wet, oil-wet, neutralwet) or heterogeneously wet (mixed wet or fractionally wet). The goal of this research is to model the detailed configuration of wetting and non-wetting phases within homogeneously and heterogeneously wet porous media. We use a dense random pack of equal spheres as a model porous medium. The geometry of the sphere pack is complex but it is known. In homogeneously wet porous media we quantify the effect of low saturations of the wetting phase on the non-wetting phase relative permeability by solving analytically the geometry of the wetting phase. At low saturations (at or near the drainage endpoint) the wetting phase exists largely in the form of pendular rings held at grain contacts. Pore throats correspond to the constriction between groups of three grains, each pair of which can be in contact. Thus the existence of these pendular rings decreases the void area available for the flowing non-wetting phase. Consequently, the existence of the pendular rings decreases the permeability of non-wetting phase. Our model explains the significant permeability reduction of the non-wetting phase with a small change in the wetting phase in a low permeability porous medium. To model heterogeneously wet porous medium, we assume that the porous medium is fractionally wet where each grain is either oil-wet or water-wet. These waterwet or oil-wet grains are distributed randomly within the porous medium. We calculate analytically the stable fluid configuration in individual pores and throats of a fractionally wet medium. The calculation is made tractable by idealizing the configurations as locally spherical (menisci) or toroidal (pendular rings.) Because the calculation of the interface position is entirely local and grain-based, it provides a single, generalized, geometric basis for computing pore-filling events during drainage as well as imbibition. This generality is essential for modeling displacements in fractionally wet media. Pore filling occurs when an interface becomes unstable in a pore throat (analogous to the Haines condition for drainage in a uniformly wet throat), when two or more interfaces come into contact and merge to form a single interface (analogous to the Melrose condition for imbibition in uniformly wet medium), or when a meniscus in a throat touches a nearby grain (a new stability criterion). The concept of tracking the fluid/fluid interfaces on each grain means that a traditional pore network is not used in the model. The calculation of phase saturation or other quantities that are conveniently computed in a network can be done with any approach for defining pore bodies and throats. The fluid/fluid interfaces are mapped from the grain-based model to the network as needed. Consequently, the model is robust as there is no difference in the model between drainage and imbibition, as all criteria are accounted for both increasing and decreasing capillary pressure.
Modeling Foam Flow in Porous Media and Applications to Eor and Acidization
(1994-05) Zhou, Zuhui; Rossen, William R.
Foams are used in the petroleum industry to divert gas in enhanced oil recovery (EOR) processes and divert acid in matrix acidization treatments. These processes are exceedingly complex, but a model based on the "limiting capillary pressure" of foam greatly simplifies the quantitative description and design of foam processes. This dissertation describes this model and applies it to EOR and well stimulation. It may be possible to bypass the daunting complexities of modeling the changes of foam texture and non-Newtonian foam rheology. By using the model of the "limiting capillary pressure", surprisingly simple and powerful conclusions can be drawn for foam plugging and flow in homogeneous reservoirs in radial geometry and in heterogeneous reservoirs with layers either isolated or in capillary equilibrium. One application of the model is in improving sweep efficiency and oil recovery in gas-injection EOR processes. With fractional-flow theory, one can estimate the velocities of the front and rear edges of a foam bank with various initial conditions. surfactant retention levels, and chase fluids behind the foam. Moreover, one can estimate the mobility of each bank and the extent of flow diversion between layers, in linear or radial geometry. Fractional-flow analysis based on extrapolated laboratory data suggests that for continuous-injection foam processes, the best swfactant is one that drives water saturation to the lowest possible value at the injected foam quality and is sensitive to permeability. In contrast, for water-alternating-gas processes, the best foam is one that degrades over a range of water saturations. Another application of the model is to predict foam diversion in matrix acidization of sandstones. This model predicts that foams can efficiently divert acid into low-permeability layers because capillary pressure makes foam less stable in these layers. The greatest diversion is obtained when foam is preceded by a swfactant preflush and followed by an acid slug that is compatible with the foam. The key to the success of such a process is the ability of a surfactant solution to immobilize the gas in previously injected foam. A process in which acid is injected continuously with foam can also achieve effective diversion. However, our model suggests that better performance is obtained by separating the foam and foam-compatible-acid slugs, and preceding the foam with a surfactant preflush.
Modeling of fluid imbibition and chemical tracer transport in porous media for oil recovery applications
(2023-08-11) Velasco Lozano, Moises; Balhoff, Matthew; Pope, Gary; Delshad, Mojdeh; Pyrcz, Michael; Javadpour, Farzam
Modeling of fluid and solute transport in porous media is fundamental to describing driving mechanisms of recovery methods before their field application, however, conventional simulations and experiments demand time and expertise. Therefore, this research work presents novel real-time solutions for spontaneous imbibition (SI) and chemical tracer transport in porous media for two-phase flow. Although imbibition tests are critical to evaluating the displacement of oil by water and chemical solutions, the existing models fail to properly estimate the entire imbibition process. Therefore, a new semi-analytical solution for SI, valid during the infinite-acting and boundary-dominated regimes, was derived. The solution was validated with experimental data for different flow geometries under diverse flow conditions and capillary pressure functions, obtaining differences of less than 5%. Additionally, a numerical model is presented to examine SI in cores with a discrete fracture by including a new transfer function in the fracture equation to account for the fluid exchange at the matrix-fracture boundary. As a result, the flow model is reduced to a one-dimensional equation that is numerically solved using finite differences, leading to the accurate and rapid modeling of fluid displacement, obtaining results comparable to two-dimensional simulations. In addition, first-ever solutions are presented for the modeling of chemical tracer transport in two-phase flow in capillary- and advective-dominated systems at core scale, accounting for hydrodynamic dispersion, partitioning, and adsorption. These novel solutions are derived using Laplace transform and a series of transformation variables that simplify the highly nonlinear advection-dispersion equation, resulting in real-time analysis with simple mathematical expressions that do not require complex numerical calculations or inversion methods. Finally, a convolutional neural network is developed to estimate residual oil saturation based on the generation of partitioning tracer responses as a function of ideal tracer profiles, where the results obtained demonstrate that this machine learning method serves as a complementary tool to significantly reduce the number of reservoir simulations. Thus, the models described in this work are innovative approaches that facilitate the analysis of fluid and tracer dynamics at core and field scales for oil recovery and subsurface applications.
Modeling of nanoparticle transport in porous media
(2012-08) Zhang, Tiantian; Bryant, Steven L.; Huh, Chun; Delshad, Mojdeh; Prodanovic, Masa; Johnston, Keith P.
The unique properties of engineered nanoparticles have many potential applications in oil reservoirs, e.g., as emulsion stabilizers for enhanced oil recovery, or as nano-sensors for reservoir characterization. Long-distance propagation (>100 m) is a prerequisite for many of these applications. With diameters between 10 to 100 nanometers, nanoparticles can easily pass through typical pore throats in reservoirs, but physicochemical interaction between nanoparticles and pore walls may still lead to significant retention. A model that accounts for the key mechanisms of nanoparticle transport and retention is essential for design purposes. In this dissertation, interactions are analyzed between nanoparticles and solid surface for their effects on nanoparticle deposition during transport with single-phase flow. The analysis suggests that the DLVO theory cannot explain the low retention concentration of nanoparticles during transport in saturated porous media. Moreover, the hydrodynamic forces are not strong enough for nanoparticle removal from rough surface. Based on different filtration mechanisms, various continuum transport models are formulated and used to simulate our nanoparticle transport experiments through water-saturated sandpacks and consolidated cores. Every model is tested on an extensive set of experimental data collected by Yu (2012) and Murphy (2012). The data enable a rigorous validation of a model. For a set of experiments injecting the same kind of nanoparticle, the deposition rate coefficients in the model are obtained by history matching of one effluent concentration history. With simple assumptions, the same coefficients are used by the model to predict the effluent histories of other experiments when experimental conditions are varied. Compared to experimental results, colloid filtration model fails to predict normalized effluent concentrations that approach unity, and the kinetic Langmuir model is inconsistent with non-zero nanoparticle retention after postflush. The two-step model, two-rate model and two-site model all have both reversible and irreversible adsorptions and can generate effluent histories similar to experimental data. However, the two-step model built based on interaction energy curve fails to fit the experimental effluent histories with delay in the leading edge but no delay in the trailing edge. The two-rate model with constant retardation factor shows a big failure in capturing the dependence of nanoparticle breakthrough delay on flow velocity and injection concentration. With independent reversible and irreversible adsorption sites the two-site model has capability to capture most features of nanoparticle transport in water-saturated porous media. For a given kind of nanoparticles, it can fit one experimental effluent history and predict others successfully with varied experimental conditions. Some deviations exist between model prediction and experimental data with pump stop and very low injection concentration (0.1 wt%). More detailed analysis of nanoparticle adsorption capacity in water-saturated sandpacks reveals that the measured irreversible adsorption capacity is always less than 35% of monolayer packing density. Generally, its value increases with higher injection concentration and lower flow velocities. Reinjection experiments suggest that the irreversible adsorption capacity has fixed value with constant injection rate and dispersion concentration, but it becomes larger if reinjection occurs with larger concentration or smaller flow rate.
Modeling of pore pressure propagation and dissipation in compressible porous media
(2017-05) Hachem, Hussein A.; El Mohtar, Chadi Said; Gilbert, Robert B. (Robert Bruce), 1965-
This research is a study of the different phenomena associated with the propagation of pore water pressure in high plasticity clays. Specifically, it addresses the pore pressure response in areas subjected to sudden increases in pore water pressure at their top boundary. The main applications of this research would be the study of pore pressure responses in grouted piezometers and the pore pressure buildup in areas with rainfall-induced landslides failures. This phenomenon of pore pressure diffusion is coupled with Terzaghi’s theory of consolidation. For that purpose, an analysis of pulse tests (consisting of measuring pore pressure response with time due to increases in pore water pressure boundary conditions) conducted by previous researchers is performed. In conjunction with the pulse tests, modified consolidation tests are also executed. The coefficients of diffusion affecting the pore pressure response in each of these cases are then evaluated. In addition, an analytical model is developed to mathematically describe the pore pressure response in clays under pressure pulses. The derivation of the differential equation describing this response makes use of Darcy’s theory of flow in porous media, where a difference in gradients causes a difference in flow patterns. The derived equation is then compared to Terzaghi’s equation of consolidation. This couples model shows that a sudden pulse of pressure causes a slower pore pressure response than the one caused by an increase of total stress. The role that pore pressure diffusion and consolidation simultaneously contribute are studied in a modified CRS consolidation setup. The mathematical modeling of these processes together is compared to the experimental results. Due to these two processes working together, at no particular point in time is there an increase of pressure at any depth in the soil that matches the initial increase of pressure application. The research also mentions the limitations of applying the derived equations. These limitations are inherently related to the simplifying assumptions presented in the theory, as well as to the complexity of porous media. Future follow-up research is also suggested.
Modeling of Real Gas Flow Behavior in Porous Media
(1993-08) Chien, Tony; Caudle, Ben H.
Due to the highly nonlinear variation of gas density and viscosity with respect to pressure, no analytical solution to the real gas diffusivity equation has ever been presented in the literature. Analytical solutions used in gas well testing and pressure analysis are based on idealized assumptions, such as small and/or constant gas compressibility and constant hydraulic diffusivity. These solutions, though widely used and easily applied, are not accurate. This research presents a detailed investigation in the behavior of real gas flow through porous media. Starting from the most fundamental flow equation a new real gas potential is implemented to transform the nonlinear flow equation into a quasi-linear diffusivity equation. The effects of pressure-dependent fluid and rock properties such as gas viscosity, compressibility, porosity and permeability are included. Advanced analytical derivations with respect to nonconstant hydraulic diffusivity are performed, and an analytical solution method is successfully developed. Multiple-rate and multiple-well systems as well as bounded reservoirs of any shape are rigorously implemented by using the principle of superposition and an unsteady-state bounding technique. Validation of the model is favorably achieved by comparison with finite-difference simulation and type curve matching. Reservoir pressures and flowing bottomhole pressures calculated by the analytical solution presented in this study are more accurate than by those methods published in the literature. The new solution method is also applicable to a broad range of pressure changes and different flow periods. This is a significant contribution to transient pressure analysis, long-term well performance tests and production forecasts in natural gas reservoirs. Moreover, since the pressure-dependent porosity and permeability are included in this study, the general solution may be applied to abnormally pressured reservoirs and tight gas sands for improved predictions of gas reserves and flow performance.
Multi-mechanistic modeling of engineered waterflooding in reactive-transport simulations
(2022-03-08) Bordeaux Rego, Fabio; Sepehrnoori, Kamy, 1951-; Delshad, Mojdeh; Mohanty, Kishore K; DiCarlo, David; Al Shalabi, Emad W
Engineered Waterflooding has gained increased attention in the past few decades as an emerging enhanced oil recovery (EOR) method. Besides the well-known waterflooding high displacement efficiency and reliable injectivity into hydrocarbon-bearing formations, the technique is very attractive because of its relatively low cost. The method consists of controlling the injected brine chemical composition aiming improved oil recovery. Laboratory and field studies indicated contradictory results, showing significant, minor, or no benefit on oil production even for similar experimental conditions. Although it is a consensus that wettability alteration is the leading cause for the improved recovery, modeling its underlying mechanisms is fundamental for successful project design and deployment. The dissertation presented here provides a comprehensive investigation of engineered waterflooding as an improved oil recovery method. It is hypothesized that changes in wettability are based on rock-fluid interactions through geochemical reactions and interfacial phenomena. Thus, a multi-mechanistic model that combines surface complexation and disjoining pressure calculations to predict contact angle and zeta-potential measurements is improved and validated. A method for determining surface complexation equilibrium constants is presented to honor several zeta-potential measurements for different ion concentrations (Na⁺, Ca²⁺, Mg²⁺, SO₄²⁻ and H⁺). In addition, a new data-driven wettability correlation is proposed to calculate contact angle based on surface complexation modeling and compared with the disjoining pressure approach. After the fundamental investigation of wettability in pore-scale, the modeling is coupled with UTCOMP-IPhreeqc, a reservoir simulator developed at The University of Texas at Austin, to study wettability alteration in core and field scale. Reactive-transport simulations are performed to history-match capillary pressure and relative permeability curves from spontaneous imbibition and coreflood experiments under controlled conditions and different lithologies (sandstone, carbonate, and shale). Geochemical calculations are conducted to study simultaneous wettability alteration mechanisms (e.g., electric double-layer expansion, multi-ion exchange, local pH increase). In addition, several physical phenomena related to changes in injected brine composition are modeled, such as clay swelling and scale deposition. Wettability and geochemical modeling are applied to investigate the synergy between engineered waterflooding and other EOR methods during reactive-transport simulations. An adsorption model for cationic surfactant is proposed based on surface complexation reactions and combined with contact angle calculations. The method is employed to match laboratory data and explore the combined effect of brine dilution and surfactant in field scale. In another study, the dissolution phenomenon, its impact on petrophysical properties, and well injectivity is investigated during water-alternating-CO₂ gas. A predictive model is proposed and validated against published coreflood data. Besides the effect of brine composition, other reservoir conditions are investigated during the water-alternating-CO₂ flood in field scale, such as mineralogy type, heterogeneity, and gravity segregation. Reactive-transport modeling has been improved significantly with recent advances in geochemical and petrophysical characterization. However, detailed simulations are usually associated with an increase in computational cost. A method is proposed to decrease the computational time during reactive-transport simulations in porous media. It is hypothesized that, if geochemical calculations can be ignored for regions under equilibrium conditions (far from the saturation front), then the computational performance would be improved without compromising simulation results. The validity of the approach is tested for three simulation cases considering different complexities (e.g., heterogeneity, wettability alteration, CO₂ solubilization in water, and dissolution)
Multifunctional foams and emulsions for subsurface applications
(2017-12) Singh, Robin, Ph. D.; Mohanty, Kishore Kumar; DiCarlo, David; Huh, Chun; Saleh, Navid; Sepehrnoori, Kamy
Foams and emulsions hold immense potential in assisting in the different stages of oil recovery processes such as enhanced oil recovery, drilling, and completion. This work is focused on developing robust, multifunctional foams or emulsions for subsurface applications, which offer unique advantages over conventional methods. The first half of the dissertation is focused on investigating novel foams stabilized using nanoparticles and/or surfactants to improve the gas enhanced oil recovery process. Gas flooding often has poor volumetric sweep efficiency due to viscous fingering, channeling, and gravity override. Foam is a promising tool to improve sweep efficiency in gas floods. It can reduce the mobility of gas by several orders of magnitude by increasing its apparent viscosity while keeping the liquid phase mobility unchanged. For sandstone reservoirs, which are typically water-wet in nature, two different approaches of foam stabilization using nanoparticles were developed. In the first approach, synergistic stabilization of foams with a mixture of hydrophilic nanoparticles and an anionic surfactant was investigated. Foam stability experiments in bulk and porous media tests showed that adding hydrophilic nanoparticles to surfactant formulations increases the foam stability. Microscopy revealed that nanoparticles are trapped in lamellae as well as at the Gibbs-Plateau borders. These nanoparticles act as physical barriers and retard the liquid drainage and the Ostwald ripening process. To fundamentally understand the role of nanoparticles in altering the foam dynamics in porous media, a high-pressure visualization experiment was performed in a 2D layered, heterogeneous porous media. This experiment showed that immiscible foams can result in significant incremental oil recovery of 25% to 34% OOIP (over waterflood). In the second approach, foam stabilized using in-situ surface-activated nanoparticles without any surfactant was explored as an EOR agent. The surface chemistry of the hydrophilic nanoparticles was tailored by adsorption of a small amount of short-chain surface modifiers to obtain surface-modified nanoparticles (SM-NP). Foam stabilization using these SM-NP was compared with that using a conventional surfactant to evaluate the potential of these SM-NP to act as an effective foaming agent. Carbonate reservoirs, which are typically highly heterogeneous and oil-wet in nature, pose additional challenges for an effective foam EOR process. Crude oils are typically detrimental to foam stability. An oil-wet carbonate will have a thin oil film on the surface and thus foam lamellae stabilization is challenging. Therefore, wettability-alteration of rock matrix toward water-wet condition using a surfactant is required to favor the in-situ foam stability. This work demonstrated for the first time a synergistic approach of using foams with wettability-altering capabilities for oil-wet systems. It was shown that optimal surfactant formulations can not only alter the wettability of a carbonate core from oil-wet to water-wet conditions, but also can significantly increase the in-situ foam stability even in presence of crude oil. The second half of the dissertation is focused on developing novel microencapsulation techniques using the concept of water-in-air powders for subsurface applications. A facile, one-step method was reported to encapsulate micro- or nano-sized hydrophilic particles using silica nanoparticles. The encapsulated particles can be released based on an external stimulus, such as a change in pH of the external continuous phase. The use of this novel carrier system was demonstrated for the delayed release of PPG particles for conformance control. The application of this technology was then explored for microencapsulating highly concentrated acids (~10 wt.% HCl) for acid treatment of shales. The advantages of these novel acid-in-air powders over conventional acid-in-oil emulsions (which are typically used for shale acidization processes) were illustrated in terms of the thermal stability, corrosion inhibition efficiency, and shale surface reactivity.