W.E. Brigham

Reaction Kinetics of In-Situ Combustion: Part 1-Observations

Continuous analysis of produced gases from a small packed bed reactor, at both isothermal and linearly increasing temperatures, has shown that combustion of crude oil in porous media follows several consecutive reactions. Molar carbon dioxide/carbon monoxide (CO/sub 2//CO) and apparent hydrogen/carbon (H/C) ratios were used to observe the transition between these reactions at different temperature levels. A new kinetic model for oxidation of crude oil in porous media is presented.

Reaction Kinetics of In-Situ Combustion: Part 2--Modeling

A model is proposed to analyze and differentiate between crude oil/oxygen reactions at different temperatures. The results of this analysis along with correlations of apparent hydrogen/carbon (H/C) ratio and molar carbon dioxide/carbon monoxide (CO/sub 2//CO) ratio indicated three major reactions at different temperatures. Low-temperature oxidation (LTO) appears to occur between the gas and liquid phases. Middle-temperature fuel deposition reactions appear to be homogeneous. The latter was found to be the rate-determining step in clean sands. Natural cores from the reservoirs were found to have different kinetic behavior than the clean sand matrices for these reasons: (1) metallic additives lower the activation energy of the combustion reaction and hence shift the rate-determining steps, and (2) clay and finer sands adsorb more fuel. The proposed kinetic model was found to be applicable to the five oils tested and hence may be generalized for application to any oil.

Flow Behavior of Foam: A Porous Micromodel Study

The flow behavior of foam in porous micromodels has been studied visually by use of etched silicon wafers. Air was injected into homogenous and heterogeneous porous media previously filled with an aqueous surfactant solution. The flow characteristics and the mobility of the injected air were determined under different conditions of pore dimensions, air injection rates, and surfactant concentrations. In the experiments, air was found to be propagated by displacement of lamellae in long bubbles flowing and extending across several pore lengths, while the liquid flowed through the network of films. Propagation of foam bubbles formed at pore constrictions by snap-off was dominant in the heterogeneous model. Liquid and/or gas was trapped in some pores. The mechanisms observed depended on pore structure and surfactant concentration. A considerable reduction of effective air mobility was observed in the presence of foam. Mobility reduction depended on flow mechanisms.

Absolute Permeability as a Function of Confining Pressure, Pore Pressure, and Temperature

This work is an investigation of the absolute permeability of unconsolidated sand and consolidated sandstone cores to distilled water as a function of the temperature of the system, confining pressure on the core and the pore pressure of the flowing liquid. The results of this study indicate that temperatures is not an important variable that needs to be reproduced in the laboratory. Confining pressure and pore pressure affect permeability in a predictable manner. This allows measurements at a lower pressure level to be extrapolated to higher pressure conditions. 21 refs.

Tracer testing for reservoir description

When a reservoir is studied in detail for an EOR project, well-to-well tracers should be used as a tool to help understand the reservoir in a quantitative way. Tracers complement the more traditional reservoir evaluation tools. This paper discusses the concepts underlying tracer testing, the analysis methods used to produce quantitative results, and the meaning of these results in terms of conceptual picture of the reservoir. Some of the limitations of these analysis methods are discussed, along with ongoing research on tracer flow.

Modifying In-Situ Combustion Performance by the Use of Water-Soluble Additives

This paper reports on experiments that were performed to study the effects of various additives on the oxidation kinetics of Californian and Venezuelan oils. Aqueous solutions of 10 metallic salts were mixed with sand and Huntington Beach, CA, oil. The mixtures were subjected to a constant flow of air and a linear heating schedule while the effluent gases were analyzed for composition. The variation in the oxygen consumption was analyzed with a model of three competing oxidation reactions. Values for the important kinetic parameters for the three reactions were obtained for each additive. Iron and tin salts were found to enhance fuel formation, while copper, nickel, and cadmium salts had no significant effects. Other experiments with a heavy Venezuelan oil showed that, contrary to earlier suggestions, the use of a ketal did not decrease fuel formation.

Effect of Temperature on Heavy Oil/Water Relative Permeabilities

In the first part of this study, the accuracy of the JBN technique for the determination of heavy oil/water relative permeabilities, and the effect of temperature on relative permeabilities is examined by giving numerical as well as experimental examples. Using the JBN technique leads to a false temperature dependence of relative permeability curves. In the second part, we present unsteady state relative permeability experiments with initial brine saturation at differing temperatures conducted using South Belridge sand and heavy oil. A new three step experimental technique and an analysis procedure were developed to test the effect of temperature on relative permeabilities. In this technique, an ambient temperature unsteady-state relative permeability run is conducted in the first stage, and following that the temperature is increased twice (i.e. 122°F and 150°F). Two phase saturation profiles along the sand pack are measured using a CT scanner. A commercial black oil simulator, coupled with a global optimization code is then used to estimate two phase relative permeabilities. Experimental saturation profiles, differential pressure and recovery data collected from both the ambient and higher temperature data are used in the numerical model. It has been observed that a single set of relative permeability curves can represent both the ambient and high temperature parts of the experiment. This suggests that relative permeability is not a function of temperature at least for the system tested.

Tracer- and Pressure-Test Analysis for Characterization of Areally Heterogeneous Reservoirs

This paper compares simulated well-to-well tracer and transient pressure tests in a quadrant of a repeated five-spot with spatial variations in permeability. Single-layer heterogeneous media with an autocorrelated and log-normal permeability distribution are generated with a stochastic moving-average method. finite-difference simulation of pressure behavior in these systems indicates that the geometric means of effective permeabilities around injection and production wells is a good approximation for the steady-state interwell permeability. A dimensionless permeability difference, defined in terms of these quantities, correlates with a heterogeneity index, defined as the product of permeability variance and a dimensionless correlation length scale. Tracer flow is simulated with a particle-tracking procedure. Simulations show that when the heterogeneity index is small, tracer response can be matched with solutions of the convection-dispersion equation with a constant dispersivity that is proportional to the heterogeneity index. For large values of this index, preferential flow paths are created that cause tracer-breakthrough curves to behave as though they result from flow in a layered system. A method is proposed to estimate the heterogeneity index from pressure-test data and thus to predict the nature of the tracer response qualitatively.

Computation and Interpretation of Miscible Displacement Performance in Heterogeneous Porous Media

Considerations of the interpretation of effluent concentration data obtained in flow through heterogeneous cores. Three models are used: Coats-Smith, porous sphere, and transverse matrix diffusion. A general analytical solution is developed by Laplace transformation, and the solutions are inverted by numerical methods. This result in a unique set of parameters for a given heterogeneous model. Criteria for design of laboratory experiments based on these results are suggested

An evaluation of field projects of steam with additives

Evaluation of the field projects published to date, in which additives have been used to improve both steamdrive and cycle steam injection. The study shows that the use of additiveswith steam can provide significant benefits over the use of steam alone. Addition of surfactant to the steam has proved to be both technically and economically successful when the proper products were used.