Showing papers in "Spe Reservoir Engineering in 1988"

Effects of Capillary Pressure on Coalescence and Phase Mobilities in Foams Flowing Through Porous Media

Abstract: The stability of foam lamellae is limited by capillary pressure. Consequently, as the fractional flow of gas in a foam is raised at a fixed gas velocity, the capillary pressure in a porous medium at first increases and then approaches a characteristic value, here called the ''limiting capillary pressure.'' If the gas fractional flow is increased after the limiting capillary pressure has been attained, coalescence coarsens foam texture, the liquid saturation remains constant, and the relative gas mobility becomes proportional to the ratio of gas-to-liquid fractional flow. The limiting capillary pressure varies with the surfactant formulation, gas velocity, and permeability of the medium.

Development of a mechanistic foam simulator: The population balance and generation by snap-off

Abstract: La mobilite de la mousse depend de la distribution de la taille des bulles dans la dispersion. Pour tenir compte de ce parametre lors de la simulation du deplacement dans un milieu poreux, les equations de conservation de la matiere sont combinees aux bilans des densites de bulles immobiles et s'ecoulant dans la mousse. Cette approche de l'ecoulement de mousse est illustree par la simulation d'un deplacement pour lequel la mousse est produite in-situ

Mechanisms of Foam Generation in Glass-Bead Packs

Abstract: La formation de mousse est etudiee par des observations visuelles. L'influence du type d'agent de surface utilise et des variations de permeabilite du milieu poreux est determinee. Trois mecanismes de formation de la mousse sont presentes et leur domaine d'application est discute en fonction du nombre capillaire

Dispersion and Reservoir Heterogeneity

Abstract: Macroscopic dispersion is the mixing, on the scale of several hundreds of grain diameters, at a point in a permeable medium that is free of boundary effects. Megascopic dispersion is the one-dimensional (1D) dispersion derived by averaging across an entire cross section. This work investigates how both dispersions vary with heterogeneity, aspect ratio, diffusion coefficient, and autocorrelation. The theoretical results are compared to existing field and laboratory data and to existing theories for limiting cases. The degree of autocorrelation in the medium determines whether or not megascopic dispersivity (dispersion coefficient divided by velocity) is uniquely defined. Large correlation distances (with respect to the medium dimensions) imply a dispersivity that grows with distance traveled. Small correlation distances imply a dispersivity that is eventually stabilized at some constant value. This value is related to the heterogeneity of the medium. On the field scale, diffusion is insignificant, but on a laboratory scale, it can stabilize the dispersivity even if the medium is correlated. Macroscopic dispersivity is sensitive to diffusion in both the laboratory and field scale. It is smaller than or equal to megascopic dispersivity, also in conformance with experimental data, and comparable to laboratory-measured dispersivity.

A multiple-porosity method for simulation of naturally fractured petroleum reservoirs

Abstract: This paper describes the application of the method of ''Multiple Interacting Continua'' (MINC) to the simulation of oil recovery in naturally fractured reservoirs. A generalization of the double-porosity technique, the MINC-method permits a fully transient description of interporosity flow, using numerical methods. The method has been successfully applied in the past to geothermal reservoir and chemical transport problems. In this paper, we present examples to demonstrate the utility of the MINC-method for modeling oil recovery mechanisms and field applications in fractured reservoirs. Specifically, results for water imbibition in individual matrix blocks obtained with the MINC method are compared with results from the conventional double-porosity method and with calculations using a detailed discretization of matrix blocks. The MINC-calculations are found to be accurate to better than 1 percent at all times, while double-porosity results can have large errors for matrix blocks of low permeability or large size. In addition, the MINC-method is used to match published results for five-spot waterfloods, and to study the coning behavior of a single well in the north China oil field. All results show that the MINC-method provides accurate predictions of the behavior of naturally fractured reservoirs, while requiring only a modest increase in computation workmore » in comparison to the double-porosity method. 21 refs., 15 figs., 5 tabs.« less

Three-Parameter Modification of the Peng-Robinson Equation of State To Improve Volumetric Predictions

Abstract: La methode Peneloux-Rauzy-Freze (PRF), utilisee pour ameliorer les estimations volumetriques en introduisant un troisieme parametre dans les equations d'etat qui en ont deux, est appliquee a l'equation Peng-Robinson. Le troisieme parametre est determine de maniere a caracteriser les fractions plus lourdes que l'heptane. La methode est appliquee a plusieurs reservoirs de petrole brut et de gaz a condensat

Measurement and Correlation of Diffusion Coefficients for CO2 and Rich-Gas Applications

Abstract: A novel in-situ method for measuring molecular diffusion coefficients of CO/sub 2/ and other solvent gases in consolidated porous media at high pressure has been developed and is described. This technique is unique because visual observations and measurements of composition are not required. Experimental diffusion coefficients are reported for CO/sub 2/ in decane up to 850 psia (5.86 MPa), for CO/sub 2/ in 0.25 N NaCl brine up to 850 psia (5.86 MPa), and for ethane in decane up to 600 psia (4.14 MPa). All tests were conducted in Berea cores saturated with liquid phase at 100/sup 0/F (311 K). Cores were oriented both vertically and horizontally to assess the effects of gravity-induced convection on the observed mass transfer. The experimental diffusion coefficients obtained from this study have also been correlated, together with literature data for methane, ethane, and propane, as a function of liquid viscosity and thermophysical properties of the diffusing gases.

Entrapment and Mobilization of Residual Oil in Bead Packs

Abstract: Etude de l'influence du nombre capillaire et du nombre de Bond sur le piegeage et le deplacement de l'huile residuelle dans des carottes constituees de perles. Le systeme utilise est CaCl 2 dans de la saumure/isopropanol/isooctane. L'influence du frittage des carottes sur le piegeage et le deplacement de l'huile residuelle est determinee. Les resultats sont compares a ceux obtenus pour des carottes en gres

Diffusion of CO2 at Reservoir Conditions: Models and Measurements

Abstract: Mathematical models are developed to describe the transport of dissolved CO/sub 2/ in a liquid phase, and results of measurements of the diffusivity of CO/sub 2/ in hydrocarbons and water at reservoir conditions are reported. The measurements were made with novel techniques based on the direct observation of the motion of an interface caused by the diffusion of CO/sub 2/ through oil or oil shielded by water. Diffusion coefficients were determined by fitting the mathematical models to the observed motion of the interfaces. This method allows the measurement of diffusion coefficients without the need to determine phase compositions and is therefore suited to measurements at elevated pressures (reservoir conditions). Measured diffusion coefficients are reported for CO/sub 2/ in pentane, decane, and hexadecane at 25/sup 0/C (77/sup 0/F) and pressures up to 6000 kPa (870 psia)). Limited measurements of CO/sub 2/ diffusion in Maljamar crude oil are also described. In addition, results of measurements for the diffusion of CO/sub 2/ in water are presented. These are the first such measurements at high pressures (up to 6000 kPa (870 pisia)). Correlations of diffusion coefficients in liquids at atmospheric pressure are shown to give reasonable estimates of diffusion coefficients for CO/sub 2/ inmore » fluids at reservoir conditions. Finally, the measured diffusion coefficients and mathematical models are used to assess the impact of diffusive mixing on CO/sub 2/ floods at various length scales to examine the relationship between laboratory-scale corefloods and field-scale displacements.« less

Chemical stability limits of water-soluble polymers used in oil recovery processes

Abstract: This work describes long-term thermal stability limits of water-soluble polymers under anaerobic conditions. Polymers investigated included polyacrylamide, xanthan, scleroglucan, cellulose sulfate, and a heteropolysaccharide of unknown structure. The primary mechanism of polyacrylamide degradation was found to be amide group hydrolysis. Interaction between hydrolyzed polyacrylamide and divalent metal ions present in solution caused significant losses in solution viscosity, and phase separation ultimately occurred in extreme conditions of high degrees of hydrolysis or high concentrations of divalent ions. The rate of hydrolysis was found to depend mostly on temperature. At 50/sup 0/C (122/sup 0/F), the rate was quite slow and polyacrylamide solutions were stable for many months, even in the presence of high concentrations of divalent ions. At 60 to 70/sup 0/C (140 to 158/sup 0/F), the rate of hydrolysis was moderate and the rate of viscosity loss depended on the precise temperature and divalent ion concentration. At 90/sup 0/C (194/sup 0/F), hydrolysis was rapid and polyacrylamide solutions were stable to precipitation only when the divalent ion concentration was less than about 200 ppm. When the divalent ion concentration was zero, solution viscosity increased because of a further expansion of the polyelectrolyte coil. The stability of xanthan was determined primarily by temperaturemore » and was independent of divalent ions. Although performance varies from xanthan to xanthan, the useful limit was generally found to be 50/sup 0/C (>122/sup 0/F).al« less

Measurements and Correlations of the Physical Properties of CO2-Heavy Crude Oil Mixtures

Abstract: La viscosite, la densite, la solubilite en dioxyde de carbone et le gonflement sont mesures pour cinq petroles lourds avant et apres saturation en dioxyde de carbone. Des correlations sont developpees pour prevoir ces proprietes physiques. Leur utilisation en est simple puisque les seuls parametres d'entree necessaires sont la temperature, la pression, la viscosite et la densite du petrole

Simulations of Naturally Fractured Reservoirs

Abstract: This paper describes a three-dimensional (3D), three-phase, black-oil model being used to simulate naturally fractured reservoirs. The program is fully implicit and can perform single-porosity, dual-porosity, or dual-permeability computations. Sample simulations are presented to illustrate the differences between the three computational techniques. Single-porosity recoveries are much larger than the recoveries predicted by the dual techniques. The dual-permeability, primary-depletion recoveries are very similar to the dual-porosity, primary-depletion recoveries, while the dual-permeability waterflood recoveries are significantly larger than the dual-porosity waterflood recoveries. Pseudocapillary pressures are generated from fine-grid, single-matrix block studies. The pseudocapillary pressures are then used in the dual-porosity simulations to account for fluid distributions in the matrix and fracture systems.

Influence of interfacial tension on gas/oil relative permeability in a gas-condensate system

Abstract: Relative permeabilities are believed to be influenced by interfacial tension through capillary forces in porous rocks. An experimental procedure was developed and used with the highly volatile methane-propane system. The objective was to measure steady state relative permeabilities as functions of interfacial tension. Interfacial tension level of the methane propane mixture, which is considered to be representative of a gas-condensate system, was varied by changing the steady state pressure of the experiment. Individual relative permeability curves obtained as a function of gas saturation approach the 45/sup 0/ diagonals for both gas and oil as the interfacial tension level is lowered. At the highest interfacial tension for which experiments were performed (0.82 dynes/cm), the relative permeability curves approached those obtained for a nitrogen-kerosene flood for which the interfacial tension is approximately 30 dynes/cm. The methane-propane mixtures were prepared in the laboratory. Compositions were determined with a chromatograph. The most important conclusions to be derived from this work are that the curvatures of the relative permeability curves diminish as the interfacial tension is reduced, the irreducible gas and liquid saturations approach zero as the interfacial tension approaches zero, and relative gas-oil permeabilities for gas-condensate reservoirs are altered from the normal relative permeabilitiesmore » only at pressures, temperatures and compositions close to the critical point.« less

Effect of Capillary Number on the Microstructure of Residual Oil in Strongly Water-Wet Sandstones

Abstract: Les consequences d'une augmentation du nombre capillaire sur la structure de l'huile residuelle piegee dans une carotte en gres mouillee par de l'eau sont etudiees a l'aide d'une phase non mouillante, le styrene, qui peut se solidifier et se separer du milieu poreux et une phase mouillante constituee de saumure contenant 2% de CaCl 2 . La distribution des tailles des gouttes d'huile residuelle est determinee par analyse d'image et a l'aide du compteur Coulter

A laboratory and field evaluation of the CO2 huff n puff process for light-oil recovery

Abstract: This paper is a laboratory and field investigation of the CO/sub 2/ huff 'n puff process for the enhanced recovery of light crude oil. The results of continuous and cyclic CO/sub 2/ displacements using a 31.2 /sup 0/API (870 kg/m/sup 3/) stock tank oil in watered-out Berea cores are presented. Fourteen single-well cyclic CO/sub 2/ field tests in south Louisianan sands are examined. Laboratory results demonstrate that the CO/sub 2/ huff 'n puff process recovers waterflood residual oil. Incremental oil recovery increased with the amount of CO/sub 2/ injected, and was not benefited by operating at the minimum miscibility pressure (MMP). Maximum ultimate incremental oil recovery required a soak period and additional water influx. Incremental oil recovery continued with a second cycle of CO/sub 2/, but a third cycle showed significant decline. Recovery factors averaging less than 2 Mscf (57 m/sup 3/) of CO/sub 2/ per barrel of incremental oil were achieved in nine out of fourteen field tests. Field results suggest that in the absence of mechanical problems, initial response improved with larger space occupied by CO/sub 2/, thicker perforation interval, and lower CO/sub 2/ reservoir viscosities; while lifetime response improved with lower prior water cut. Field results confirmmore » that the CO/sub 2/ huff 'n puff process recovers waterflood residual oil, and that a second cycle can be successful.« less

Automatic History Matching With Variable-Metric Methods

Abstract: Deux methodes metriques variables ― celle de Broyden/Fletcher/Goldfarb/Shanno et celle de l'auto-dimensionnement ― sont utilisees pour evaluer les proprietes du systeme roche magasin fluide telles que la porosite et la permeabilite. Leur aptitude a simuler le reservoir au cours de l'injection d'eau est discutee

Sweep Improvement in CO2 Flooding by Use of Foaming Agents

Abstract: Les agents moussants, qui sont des sels d'ammonium d'alcool sulfate et ethoxyle, sont selectionnes en fonction de leur stabilite, testee en laboratoire. L'influence de ces agents sur les performances de la recuperation assistee par injection de dioxyde de carbone est etudiee sur des carottes

Effect of Solvent on Steam Recovery of Heavy Oil

Abstract: Solvents and light ends of crudes are frequently used as diluents to facilitate pumping and pipeline transportation of heavy crudes. The use of solvent alone for in-situ recovery of heavy oil tends to be limited because of its high cost; however, the use of solvent as an additive to steam processes has been tested both in the laboratory and in the field. The results of these tests are mixed. In this study, the authors use numerical experiments to delineate the recovery mechanism of a steam-slug process when solvents are present. A good understanding of the mechanism will help provide an interpretation of the conditions under which solvents can improve steam oil recovery. The study focuses on the use of small quantities of solvent-i.e., no more than 10% of the steam volume.

Numerical simulation of naturally fractured reservoirs

Abstract: The most important and difficult aspect of modeling a naturally fractured reservoir is the correct calculation of the exchange of fluids between the matrix rock and the surrounding fractures. Several authors have published alternative techniques for handling this problem over the past few years. However, because each of these alternatives has some limitations, a new and more general technique has been developed. This new technique is used to simulate matrix/fracture exchange with special emphasis on the gravity forces included in the exchange terms. The exchange terms and the gravity forces within the exchange terms simulate the behavior of a single matrix block surrounded by fractures that may contain several different fluids. The gravity forces are internally calculated as functions of saturation. This technique has been incorporated into a new three-dimensional (3D), three-phase, fully implicit model for simulating fluid flow in a naturally fractured reservoir. The description of the porous medium might include highly fractured, microfractured, and nonfractured regions. Several examples explain the use of a new naturally fractured reservoir model and the essential differences between the new approach and those used in earlier naturally fractured reservoir models.

Dynamics of Subcritical CO2/Brine Floods for Heavy-Oil Recovery

Abstract: Immiscible CO/sub 2/ flooding is an important, field-proven heavy-oil recovery method, particularly suited for thin, marginal, or otherwise poor heavy-oil reservoirs, where thermal recovery processes are likely to be uneconomical. This paper describes the dynamics of this recovery technique on the basis of experiments conducted in a scaled model. The experiments represent a medium-heavy oil (1032 mPa . s at 23/sup 0/C (1,032 cp at 73/sup 0/F)) occurring in a shallow, thin sand. CO/sub 2/ was injected together with brine at subcritical conditions (5.5 MPa and 21 to 23/sup 0/C (800 psi and 70 to 73/sup 0/F)). The CO/sub 2/ and brine superficial velocities were varied from 0.18 to 2.9 m/d (0.6 to 9.5 ft/D). This broad range of velocities permitted the study of the effect of the viscous, diffusive, and gravitational forces on the CO/sub 2/ slug (20% HCPV) process for heavy-oil recovery. It was found that viscous forces completely dominant CO/sub 2/ injection. Also, the mass transfer between CO/sub 2/ and oil had a stabilizing effect on the brine injection. Although the molecular diffusion of CO/sub 2/ in oil was high, it was not high enough to mobilize appreciable amounts of oil from uninvaded zones. The scaled experimentmore » results showed that oil recoveries at CO/sub 2/ and brine breakthroughs were rate-dependent. While recovery at CO/sub 2/ breakthrough decreased with increasing rate, recovery at brine breakthrough increased. Reduction of interfacial tension (IFT) between brine and oil, leading to the formation of brine-in-oil emulsions, was found to be an additional effective mechanism of heavy-oil recovery by CO/sub 2//brine injection.« less

An Approximate Model With Physically Interpretable Parameters for Representing Miscible Viscous Fingering

Abstract: Developpement d'une nouvelle fonction de digitation pour modeliser les fractions solvant/petrole au cours de deplacements miscibles dans un milieu poreux. L'etude est realisee pour des deplacements horizontaux et verticaux. Le modele est teste a partir de donnees trouvees dans la litterature

Vapor-density measurement for estimating minimum miscibility pressure

Abstract: An experimental method (Vapor Density Test) is described which uses the solvency (density) properties of carbon dioxide and oil composition to determine the minimum miscibility pressure (MMP) of carbon dioxide with crude oils. Empirical methods have been described in the literature which relate the MMP to the density of carbon dioxide, oil composition, and solvent properties of carbon dioxide. It has also been proposed that a density comparison of impure carbon dioxide and pure carbon dioxide could be used to predict the MMP for impure carbon dioxide if the pure carbon dioxide MMP was known. The ''Vapor Density'' method is a dynamic test which directly measures the density of the injection gas rich phase versus pressure. This provides direct measurements of the ability of the injected gas to extract components from the crude oil. This method is as easily applied to impure carbon dioxide or hydrocarbon injection gases as to pure carbon dioxide. The measurements are done in a constant volume visual PVT cell. In addition to measuring the upper phase density, the volume of the liquid (lower phase) is monitored to aid in the MMP determination. Experiments have been completed on crude oils over the 83/sup 0/ to 220/supmore » 0/F range. The MMP is easily estimated at low temperatures. A method is proposed to use the ''Vapor Density'' at higher temperatures where the MMP is not as apparent.« less

Effect of WAG Injection and Rock Wettability on Oil Recovery During CO2 Flooding

Abstract: Previous studies to determine the extent of oil trapping by water during CO/sub 2/ water-alternating-gas (WAG) flooding have shown that rock wettability strongly affects this trapping. A significant trapping occurs in water-wet rock, and less trapping occurs in oil-wet rock. This paper presents laboratory results of Devonian crude oil displacement from watered-out Berea and reservoir cores by use of continuous CO/sub 2/ injection, single-slug CO/sub 2/ injection (followed by water), and CO/sub 2/ WAG injection at miscible reservoir conditions of 120/sup 0/F and 2,500 psig (49/sup 0/C and 17.2 MPa). The reservoir cores used in this study were mixed-wet (Devonian and Muddy formations) and oil-wet (Tensleep formation). The Berea cores used had their wettability artificially altered to simulate these natural wettabilities. The X-ray photoelectron spectroscopic (XPS) method for measuring carbon content of rock surface was used to provide a qualitative measurement of wettability of the rock samples. The results of the study indicated that the experimental wettability-altering technique came close to duplicating reservoir rock wettability. The oil recovery data at the end of 1 PV fluid injection (continuous CO/sub 2/ or WAG CO/sub 2/) indicated that (1) in preferentially water-wet Berea cores, more than 45% of the waterflood residual oilmore » trapped by CO/sub 2/ WAG; (2) in mixed-wettability Berea cores, 15 to 20% of the waterflood residual oil was trapped; and (3) in oil-wet Berea cores, less than 5% residual oil was trapped.« less

Some invariant solutions to two-phase fluid displacement problems including capillary effect

Abstract: Analytical investigation of the two-phase displacement problem that considers capillary force is one of the most important and difficult problems in the theory of fluid flow through porous media. This paper presents some invariant solutions on the subject, including a self-similar solution for the axisymmetric case, a self-similar solution in a linear, isoclinal reservoir that considers the effects of gravity and capillary forces simultaneously, and a progressive wave solution corresponding to a stabilized zone of saturation distribution. The relations and differences among (1) a model that completely includes capillary effect, (2) a model that considers capillary action partially and implicitly (the Buckley-Leverett model), and (3) a model that completely ignores capillary effect are indicated and discussed.

An Analysis of Upstream Differencing

Abstract: A complete convergence analysis is carried out for upstream differencing as applied to one-dimensional (1D) tilted reservoirs experiencing gravity-segregation effects and possible countercurrent flows. It is shown that the standard upstream method converges to the correct physical solution of this problem, provided that an appropriate stability condition holds. Results from the theory of monotone-difference schemes are used. It is concluded that in addition to the practical advantages of the upstream formulation, there is also a strong theoretical justification for use of upstream techniques in multidimensional reservoir simulation.

Effects of spreading and nonspreading oils on foam propagation through porous media

Abstract: Experiments show that a spreading oil increases the time for foam generation and decreases the speed of foam propagation in porous medium. It also breaks a foam faster than a nonspreading oil. These findings may be important in interpreting results of different foam displacement experiments and therefore surfactant selection.

A Thermodynamic Correlation for the Minimum Miscibility Pressure in CO2 Flooding of Petroleum Reservoirs

Abstract: A graphic equation-of-state (EOS)-generated correlation for the minimum miscibility pressure (MMP) of CO/sub 2//crude-oil displacements is presented, along with a brief review of 17 other MMP correlations. The MMP is estimated as the cricondenbar or first-contact miscibility pressure of the pure or impure CO/sub 2//crude-oil system in which the C/sub 5+/ oil fraction is modeled as a single normal alkane of equivalent molecular weight. The correlation accounts for all the experimentally observed trends in MMP in a consistent manner and is independent of any CO/sub 2//crude-oil data base. A correction is introduced, however, to prevent a predicted increase in the MMP with decreasing temperature at low temperatures for high-molecular-weight oils. The average predicted-MMP/experimental-MMP ratio for 157 CO/sub 2//crude-oil MMP values is 1.09, with a standard deviation of 0.19. Unlike other correlations, specifically those relating MMP with CO/sub 2/ density, a decrease in MMP with temperature at elevated temperatures (>120/sup 0/C (>248/sup 0/F)) is predicted.

Hydrolytic Stability of Alkylethoxy Sulfates

Abstract: Sulfate surfactants are being proposed by industry for use in moderate-temperature surfactant floods. Sulfates are also being considered by some groups for use in CO/sub 2/ mobility control and surfactant/alkaline floods. Data from this study show that the maximum applicable temperatures for sulfates under these pH conditions are much lower than for neutral pH conditions. Rate equations are derived from Arrhenius data on the basis of observed decomposition mechanisms. The equations are used to calculate surfactant lifetimes and maximum temperature limits at various reservoir conditions. The maximum temperatures and lifetimes are functions of pH and brine composition.

Molecular degradation, injectivity, and elastic properties of polymer solutions

Abstract: New features of polymer rheology in porous media were observed when hydrolyzed polyacrylamide (HPAM) solutions were flowed through sandstone, gravel packs, and glass-bead packs at high rates. Independent measurement of elongational viscosity, /sub e/, with a ductless-siphon technique demonstrates that the enhanced resistance seen at high flow rates is not directly proportional to /sub e/. Furthermore, significant permeability trends in resistance factor and mechanical degradation are observed when plotted vs. strain rate. When these results are translated to field flow rates and geometries, they indicate that HPAM solutions can be injected at reasonable injection pressures with minimal viscosity losses, provided that perforated completions are designed with either sufficient perforation density or perforation size.

Reaction Kinetics of Fuel Formation for In-Situ Combustion

Abstract: In-situ combustion is receiving new interest as a viable alternative to the other thermal methods of heavy crude oil recovery. In this method, thermal energy is generated in-situ by creating an oil combustion zone that is driven through the reservoir by continuous air injection. While the various oil oxidation reactions have been adequately studied and modeled, little information is available regarding the fuel formation process that takes place ahead of the combustion zone. The goal of this study was to investigate the reactions that contribute to this process and obtain generalized kinetic equations for them. An experimental apparatus was built wherein a small sample of an oil/sand mixture can be pyrolyzed at a constant rate of heating, to temperatures normally encountered in combustion field applications, while nitrogen is continuously sweeping the sample. The effect on fuel formation of pressure, rate of heating, porous medium composition, and type of oil were investigated in an experimental program totaling 12 runs. Data from previously made oxidation experiments were also used. General conclusions reached in this study are: (1) the fuel is formed as a result of two successive cracking reactions that the oil undergoes at temperatures above 550/sup 0/F; distillation of crude oilmore » at temperatures below 550/sup 0/F plays an important role in shaping the nature and extent of the cracking reactions; (3) the operating pressure and rate of heating affect the fuel formation process only through the influences exerted on distillation; (4) clay minerals have a catalytic effect on the cracking reactions, especially on coking; and (5) the asphaltene fraction of a crude oil is a parameter which correlates with the fuel content of that oil. 51 refs., 73 figs., 21 tabs.« less