Combustion Fronts In Porous Media Research Articles

Thermal Imaging To Visualize and Characterize Combustion Fronts in Porous Media

We developed a novel technique based upon time-lapse infrared (IR) images to relate the effects of crude-oil oxidation kinetics on flow during one-dimensional homogeneous and heterogeneous laboratory-scale combustion tube experiments. We performed combustion tube experiments under variable conditions including different sands (i.e., grain-size distribution), air injection rate history (constant versus variable), degree of packing heterogeneity, and reaction heterogeneity. The latter is achieved by using reaction enhancing nanoparticles in controlled packing configurations. During every experiment, we obtain high-resolution IR images of the outer wall of the combustion tube that we calibrate using point-wise temperature measurements from a thermocouple. Here, a new experimental workflow that uses these images and combines knowledge obtained from kinetic cell experiments is used to isolate the spatial zones within the tube where so-called low-temperature and high-temperature oxidation (pseudoreaction regimes) occurs during combustion tube experiments for the first time. Additionally, the IR imaging technique is shown to provide new insight into the propagation of the combustion front in homogeneous and heterogeneous systems and, importantly, visualizes gravity drainage of hot oil.

A Stochastic Model for the Dynamics of Combustion Fronts in Porous Media

Based on an analytical deterministic model previously developed, a probabilistic model is constructed to describe the behavior of the heat wave that propagates through the porous medium. As a first approximation in this article, it is considered that the coefficient advective (speed of the wave front) is a spatially random variable characterized by well-defined statistical parameters. The effects on this wave when noise multiplicative is introduced in the front velocity with a correlation coefficient exponentially decaying has been studied.

Modeling and simulation of combustion fronts in porous media

We study a model for forward propagation of a combustion front through a porous medium. The reaction involves oxygen and a solid fuel. We assume that this solid fuel depends on the space variable. We also assume that the amount of gas produced by the reaction is equal to the amount of gas consumed by it. By actual solutions, we prove the existence and uniqueness of solution of the model. We show that temperature is non-decreasing function of time. We use the similarity variable to transform the system of partial differential equations, describing the problem under consideration, into a boundary value problem of coupled ordinary differential equations and an efficient numerical technique is implemented to solve the reduced system. The results are presented graphically and discussed. It is discovered that the heat transfer and species consumption are significantly influenced by the Frank–Kamenetskii number.

An application of the monotone iterative method to a combustion problem in porous media

Problems related to combustion fronts in porous media have been studied by many authors recently, see e.g. [Y. Akkutlu, Y.C. Yortsos, The dynamics of in-situ combustion fronts in porous media, Combust. Flame 134 (2003) 239–247; J.C. da Mota, W. Dantas, D. Marchesin, Combustion fronts in porous media, SIAM J. Appl. Math. 62 (2002) 2175–2198; D.A. Schult, B.J. Matkowsky, V.A. Volpert, A.C. Fernandez-Pello, Forced forward smolder combustion, Combust. Flame 104 (1996) 1–26]. Most of this interest is due to the combustion process for oil recovery. In this paper we construct monotone iteractions for a Cauchy problem arising from a combustion model in a porous medium derived in [J.C. da Mota, S. Schecter, Combustion fronts in a porous medium with two layers, J. Dynam. Differential Equations 18 (3) (2006) 615–665]. We conclude that the monotone iteractions converge to a unique solution of this Cauchy problem, globally in time.

Influence of In-Situ Fuel Deposition on Air Injection and Combustion Processes

Abstract Sustained propagation of a combustion front is necessary for improved oil recovery during an air injection and in situ combustion process. The front is a sharp diffusive layer and involves the added complexities of reactions. In this work, the combustion front is represented by two oxidation reactions: a high-temperature fuel burning reaction and a low-temperature fuel generating reaction. Due to distinct reaction kinetics and stoichiometry, the reactions occur in sequential regions within a finite separation distance in the reservoir. Interaction of these regions and its overall influence on the front propagation are investigated locally using an analytical approach based on large activation energies of the reactions. Reservoir conditions under which the regions could travel with a common propagation speed is identified and their limits of coherence are investigated in the presence of external heat losses. Consequently, a new intricate relationship between the reservoir heat loss rate and separation distance of the reaction regions is found and formulated. The regions propagate closely spaced, thus minimizing the influence of deleterious heat losses and improving the combustion process performance. This two-reaction self-sustainability mechanism keeps the combustion front propagating steadily, even though under the same conditions front extinction has been predicted for the equivalent single-reaction problem. The work emphasizes the importance of local nonlinear chemical processes during air injection. Introduction Propagation of combustion fronts in porous media has been studied extensively in the filtration combustion literature. It is a subject of interest to a variety of applications, ranging from in-situ combustion for the recovery of heavy and light oils to catalyst regeneration, coal gasification, smoldering, waste incineration, ore calcinations or the high-temperature synthesis of powdered materials(1). The fuel may pre-exist as part of the solid matrix or, as in the case of in-situ combustion, it may be created by local processes such as pyrolysis and low-temperature oxidation reactions. Dynamics of filtration combustion is influenced by the flow of injected and produced gases, the heat and mass transfer in the porous medium and the rates of reactions. An analytical treatment can be accomplished assuming a sharp exothermic oxidation front using large activation energy asymptotics; a technique widely considered to investigate laminar flames in the absence of a porous material(2,3). Akkutlu and Yortsos(4,5) considered the application of the technique for modeling dry forward in situ combustion fronts in porous media. They investigated the effects of reservoir heat losses(4) and the impact of reservoir heterogeneity(5) on ignition, sustained front propagation and extinction. Their investigations were based on a main (high-temperature) oxidation reaction only, however. In this paper, the presence of an additional oxidation reaction occurring at lower temperatures is considered. The latter precedes the main combustion region, takes place at lower temperatures and generates the fuel necessary for sustained propagation of the former. Under certain conditions, the two reaction regions are thermally coupled, in which case they may propagate coherently, albeit at a finite distance from each other. Otherwise, they become uncoupled, with the region of low-temperature oxidation traveling far ahead at higher velocities.

Quenching and propagation of combustion fronts in porous media

In this short note we study the model of subsonic detonation introduced by Sivashinsky. The model is described by the system of reaction-diffusion equations involving temperature, pressure and concentration of deficient reactant. It is shown that initial data with small support lead to quenching (decay of solution). In contrast, initial data with support large enough lead to propagation with finite velocity.

Percolation Phenomena in Filtration Combustion

Using a pore-network model, we study the effect of randomness in the solid fuel distribution on the propagation of filtration combustion fronts in porous media. Both a complex pore-network model for full filtration combustion and a more simplified gasless combustion model are used. We find that the minimum threshold (akin to a “percolation threshold”) for the fuel distribution is a function of the kinetic and heat-transfer parameters and can vary over a wide range. The balance between heat transfer and reaction kinetics endows the system with a behavior more complex than simple percolation, which was earlier suggested as a model for such systems. The long-range effect of heat conduction acts to move the behavior away from true percolation behavior. Conversely, the effect of heat losses is sufficient to lead to extinction (thus, to “nonpercolation”) even for systems with fully occupied fuel sites. In either case, the availability of the fuel and its distribution in space are important parameters in the process.

The dynamics of in-situ combustion fronts in porous media

The sustained propagation of combustion fronts in porous media is a necessary condition for the success of in situ combustion for oil recovery. Compared to other recovery methods, in situ combustion involves the complexity of exothermic reactions and temperature-dependent chemical kinetics. In the presence of heat losses, the possibility of ignition and extinction also exists. In this paper, we address some of these issues by studying the properties of forward combustion fronts propagating at a constant velocity in the presence of heat losses. We extend the analytical method used in smoldering combustion [7], to derive expressions for temperature and concentration profiles and the velocity of the combustion front, under both adiabatic and non-adiabatic conditions. Heat losses are assumed to be relatively weak and they are expressed using two modes: 1) a convective type, using an overall heat transfer coefficient; and, 2) a conductive type, for heat transfer by transverse conduction to infinitely large surrounding formations. In their presence we derive multiple steady-state solutions with stable low and high temperature branches, and an unstable intermediate branch. Conditions for self-sustaining front propagation are investigated as a function of injection and reservoir properties. The extinction threshold is expressed in terms of the system properties. An explicit expression is also obtained for the effective heat transfer coefficient in terms of the reservoir thickness and the front propagation speed. This coefficient is not only dependent on the thermal properties of the porous medium but also on the front dynamics.

Combustion Fronts in Porous Media

The equations governing combustion in situ in petroleum reservoirs are cast in a way that is appropriate to the study of the time asymptotic fundamental waves: rarefactions and shocks. The physical diffusion terms are maintained so that the internal structure of shocks can be analyzed. In this work, we determine the planar traveling wave solutions for the system of three evolution equations modeling combustion in two phase flow, obtained by neglecting heat losses and volume change effects. The chemical reaction rate is governed by Arrhenius' reaction rate law. Our analysis is intended to capture the main effect of combustion: the reduction of oil viscosity due to temperature increase and its practical result---the increase in oil recovery. It also is intended to resolve the difficulty introduced by the singularity in the Arrhenius reaction rate law. Our analysis shows that the combustion wave is represented by a heteroclinic connection in a nonhyperbolic system of three ordinary differential equations. It follows that numerical simulations need to resolve completely the small parabolic terms in the model to be reliable. The analysis also indicates that the phase diagram should be stable under perturbations of interest. Thus, the general structure of combustion waves in a more realistic model should be similar to the one we found here.

Asymptotic structure of planar nonadiabatic reverse combustion fronts in porous media

A leading-order analytic analysis of the structure of a planar nonadiabatic reverse combustion (RC) front in a combustible porous medium has been performed by use of matched asymptotic expansions in the activation energy of the combusion reaction. The model considers the irreversible reaction of oxygen in a feed gas flow with an excess of a single-component gaseous fuel devolatilized from the medium, according to one-step, first-order kinetics characterized by a large activation energy. A heat loss term linear in the local temperature difference and an infinite effective Lewis number are assumed for this two-phase combustion process. The analysis determines conditions for the extinction of the steady RC front in terms of the heat loss strength and oxidant flux, and shows the existence of two solutions for heat losses below the extinction value. The predicted dependence of the steady front velocity and temperature on the heat loss intensity agree qualitatively with experimental observations.

Stability of Moving Combustion Fronts in Porous Media

Abstract The stability of moving combustion fronts during underground combustion processes is analyzed. The behavior of small deformations in front configuration is studied using knew stability theory and relatively simple models of the combustion processes. In this way, the main physical phenomena that influence stability can be physical phenomena that influence stability can be distinguished clearly. For wet combustion processes, where both air and water are injected, front stability is affected, not only by the ratio of the mobilities of fluids flowing ahead of and behind the front, but also by heat transport near the front and by expansion accompanying vaporization of water at the front. Even more interesting is a "reverse mobility" effect predicted by the analysis. Under some conditions at relatively high air to water injection ratios, fluid flow, and the heat produced by combustion interact in such a way that normally "favorable" mobility ratios become unfavorable. That is, existence of a low mobility in the region of two-phase flow of air and water behind the front actually can promote front instability. For dry combustion the beat transport and reverse mobility effects on stability do not occur and the combustion fronts are typically neither highly stable nor highly unstable; That is, the effective mobility ratio is near unity. Introduction Thermal processes, such as underground combustion and steam drive, are prime candidates for supplementing primary recovery techniques in reservoirs containing highly viscous crude oils. Thermal methods also have been considered for tertiary recovery of lighter oils. Chemical flooding seems currently to be the preferred process, however, for this latter application. As is true for all recovery schemes, the over-all effectiveness of thermal processes depends on the injected fluids contacting a substantial portion of the reservoir, that is, on achieving good sweep efficiency. Of course, the amount of the reservoir swept depends on various factors, including reservoir heterogeneity and the pattern of wells. But studying the stability of moving displacement fronts in an idealized homogeneous porous medium provides useful information that, at a minimum, provides useful information that, at a minimum, gives a qualitative idea of what to expect in more complex situations. For example, if the front is unstable even in the simple case of a homogeneous medium, sweep efficiency is likely to be poor for any realistic reservoir conditions. It has been known for some years that a ratio between the mobilities () of displacing and displaced fluids that exceeds unity gives rise to a destabilizing influence on the moving front between them. Only recently has it been shown that other effects on front stability can be equally important during thermal recovery processes. Analysis of a simple situation with steam condensing and displacing water at a moving front indicated that the adverse mobility ratio because of low steam viscosity sometimes could be offset completely by two stabilizing effects. This conclusion is consistent with Baker's laboratory experiments on steam displacement that showed that moving condensation fronts are usually stable. One stabilizing effect at a condensation front is contraction accompanying condensation of a given mass of swam, a process which extracts mechanical energy from the flow. The other effect is heat transport in the water region, where the temperature varies from the saturation temperature at the front to ambient conditions far ahead of the front. The rate of front advance is controlled by the rate of condensation, high front velocities being associated with low condensation rates. The condensation rate, in turn, is limited by the rate at which the latent heat released at the front can be transported into the water. When the front is deformed as shown in Fig. 1 points such as P are exposed to a large amount of cool liquid so that the local heat flux increases. As a result, the local condensation rate increases at P, and the local front velocity decreases there, producing a stabilizing effect. This qualitative explanation of the transport effect on stability is an improvement over that given in the original paper. SPEJ P. 423