The CT imaging technique together with temperature and pressure measurements were used to follow the steam propagation during steam and steam foam injection experiments in a three dimensional laboratory steam injection model. The advantages and disadvantages of different geometries were examined to find out which could best represent radial and gravity override flows and also fit the dimensions of the scanning field of the CT scanner. During experiments, steam was injected continuously at a constant rate into the water saturated model and CT scans were taken at six different cross sections of the model. Pressure and temperature data were collected with time at three different levels in the model. During steam injection experiments, the saturations obtained by CT matched well with the temperature data. That is, the steam override as observed by temperature data was also clearly seen on the CT pictures. During the runs where foam was present, the saturation distributions obtained from CT pictures showed a piston like displacement. However, the temperature distributions were different depending on the type of steam foam process used. The results clearly show that the pressure/temperature data alone are not sufficient to study steam foam in the presence of non-condensible gas.

Summary The use of additives to improve both steamdrive and cyclic steam injection in field projects has been tested under a variety of conditions. This technique attempts to reduce gravity override and channeling of the steam by foam generation. Another mechanism appears to be "detergent" cleaning near wellbores by surface-active agents. When successful, this technology seems to be economic even at a low oil price. The results, however, have ranged from excellent to negative. In this paper, we attempt to evaluate the field projects published to date. The results of this study show that the use of additives with steam can provide significant benefits over the use of steam alone. Indeed, addition of surfactant to the steam has proved to be both technically and economically successful when the proper products and procedures were used. Caustics have given mixed results but seem to have been effective in at least one cyclic-steam project.

Summary Experiments 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.

The CT imaging technique together with temperature and pressure measurements were used to follow the steam propagation during steam and steam foam injection experiments in a three dimensional laboratory steam injection model. During the design period, the advantages and disadvantages of different geometries were examined to find out which could best represent radial and gravity override flows and also fit the dimensions of the scanning field of the CT scanner. As a result of this analysis a 3D rectangular box with dimensions 20x20x7.5 cm was constructed. This box simulates one quarter of a five spot pattern. Aluminum, Teflon™ and Fiberfrax™ were chosen as supporting and insulating materials. Teflon™ was placed between the porous medium and the aluminum shell so that the rate of heat transfer in the porous medium would be much faster than that in the aluminum during a steam injection run. During experiments, steam was injected continuously at a constant rate into the water saturated model and CT scans were taken at six different cross sections of the model. Pressure and temperature data were collected with time at three different levels in the model. CT pictures and three dimensional temperature distributions were compared and analyzed in terms of observed steam zone at each section. To do that, CT numbers within the scan section were used to determine the steam and water zones, and with the aid of x-ray pictures the position and propagation of the steam zone were determined. In addition, using the three dimensional temperature distribution measurements at the same times, steam displacement fronts could be drawn at the scan section locations. These pictures and drawings were used to compare the results obtained from classical temperature-pressure monitoring and from CT scans. During steam injection experiments the saturations obtained by CT matched well with the temperature data. That is, the steam override as observed by temperature data was also clearly seen on the CT pictures. During the runs where foam was present, the saturation distributions obtained from CT pictures showed a piston like displacement. However, the temperature distributions were different depending on the type of steam foam process used. During the experiment which included non-condensible gas (nitrogen) injection, the temperature distributions, contrary to the saturation distributions, still indicated the presence of steam override, although the override was reduced by the foam. However, when there was no nitrogen the temperature distributions followed the saturation distributions. This may possibly indicate that the nitrogen foam ahead of steam foam caused the difference between temperature and saturation distributions. These results clearly show that the pressure/temperature data alone are not sufficient to study steam foam in the presence of non-condensible gas.

Summary Computation of miscible displacement performance requires an estimate of the amount of mixing in the reservoir. Dispersion coefficients measured from displacements in laboratory cores are often used to compute reservoir performance. This paper considers interpretation of effluent flowing concentration data obtained from heterogeneous cores by use of the Coats-Smith, porous-sphere, and transverse-matrix-diffusion heterogeneous models. Analytical solutions to the three heterogeneous models are presented in Laplace space. Approximate solutions for short- and long-time effluent flowing concentrations, developed from simplification of the Laplace transformation solution, are used to develop practical methods of interpreting effluent concentration data to determine model parameters. Criteria for design of laboratory experiments based on these results are suggested.

The efficiency of a steamflood may be increased by the use of surfactants that spontaneously generate steam foam when injected into an oil reservoir. Ideally the foam preferentally forms in high permeability streaks and oil depleted regions of the reservoir through which the steam would otherwise channel. This report describes an experimental programme conducted study the foam-forming characteristics of a range of different surfactants. Both commercially-available, and experimental surfactants were tested in a one-dimensional sandpack under controlled conditions of pressures and temperatures similar to those encountered in California oil fields. Steam and nitrogen were continuously injected into the sandpack which contained neither clay nor oil. The surfactant solutions were injected in discrete slugs of a finite duration allowing transient phenomena such as the persistence of the foam to be studied. Under the conditions of the experiment, long chain alpha olefin sulphonate surfactants were found to generate the strongest foams. Internal olefin sulphonates, linear toluene sulphonates and linear xylene sulphonate surfactants generated just as strong foams but only at successively higher concentrations. It was fond that the strength of the foam produced by a surfactant of a particular chemical structure increased with increasing alkyl chain length. 30 refs., 91 figs., 31 tabs.

Summary This paper presents some new close-form analytical solutions to equations describing radial transport of reactive tracers in porous media under conditions of tracer adsorption, nonuniform convection, and variable dispersion coefficient. Three different types of variable dispersion coefficients were considered and exact solutions presented in Laplace space. The special case where shear mixing or convection dominates dispersion, which is important for tracer test studies, was programmed on a computer to obtain concentration profiles for the continuous- and slug-injection test models.

Summary A new correlation and set of pressure-response and pressure-derivative type curves are presented for interference test analysis. The influence of wellbore storage and skin effects at active and observation wells on interference pressure response is examined. In the case of wellbore storage and skin in one well, the correlating parameter [CDe2s]CD/rD2 is used to combine wellbore storage and skin variables in a way that makes it possible to display, on a single type curve, all interference test data that would ordinarily require a number of type curves for various combinations of CD/rD2 and CDe2s. The product of the correlating parameter is used when wellbore storage and skin effects are active at both wells. The difference in the shapes of the single-well storage type curves compared to the two-well storage case at early times can be used as a diagnostic feature in interference testing.

SummaryThis paper reports on the design and execution of a field experiment on recovery of heavy oils by steamdrive enhanced by additives. The goal of this project was to study the effect of injection of a commercial surfactant (Suntech IV™) and N2 on the behavior of a conventional steamdrive. Because the laboratory studies leading to the design and implementation of this field experiment have been referenced many times, we emphasize here the field data obtained in reservoir definition, monitoring of the experiment's progress, and production evaluation in a heavy-oil reservoir. Several standard and experimental analytical methods were applied, and their validity in the Kern River field test is discussed.Three slugs of surfactant and N2 were injected at different rates. Analysis of the results shows a considerable improvement in oil recovery by steamdrive caused by the addition of surfactant and N2 to the steam. The changes in production behavior of the reservoir caused by the additives are analyzed and discussed. Although the economics of this project is difficult to determine at this point, it looks promising.

ABSTRACT This paper concerns the application of frontal advance theory to displacement processes in heterogeneous porous media. The assumptions under which a generalized frontal advance equation can be used to describe a flow process in a heterogeneous porous medium are examined. Material balance equations are derived based on these assumptions, and the theory is illustrated by application to the Dykstra-Parsons model of flow in noncommunicating layers. We show that the resulting formulation can be used to forecast performance and to solve the inverse problem: the determination of a permeability distribution from displacement data. This approach can also be used to determine pseudorelative permeability curves appropriate to a one-dimensional description of a layered system. We also consider the use of pseudorelative permeabilities in simulation studies to represent the effects of reservoir heterogeneities with length scales smaller than a grid block. The dependence of process performance and pseudorelative permeabilities on scale is described. Results show that frontal advance theory may be applied to flow in heterogeneous porous media for processes that exhibit linear characteristics. In such a process, a given saturation travels at a constant velocity through the porous medium. Displacement performance for the two-dimensional Dykstra-Parsons model is exactly duplicated using one-dimensional frontal advance theory for unit mobility ratio displacements. One-dimensional theory reproduces the qualitative performance of the two-dimensional model for nonunit mobility ratios, but exact quantitative agreement is not obtained, because the characteristics are nonlinear. Pseudorelative permeabilities determined for a system of noncommunicating layers apply to any scale as long as the layer structure does not change with system length. However, for processes that are not purely convective, process performance varies with the scale of the displacement Thus, pseudorelative permeabilities obtained from flow processes that are not purely convective are only applicable to the scale at which the displacement data was measured.

ABSTRACT This paper discusses the effects of some parameters on the in-situ combustion process. The paper is in two parts. The first part discusses a laboratory in-situ combustion tube run. Important design parameters such as fuel concentration, air requirement, oxygen utilization efficiency and combustion front velocity may be determined from the analysis of laboratory tube run data. The second part of the paper discusses numerical simulation of the laboratory tube run and results from in-situ combustion simulation studies. A thermal simulator was used to investigate the effects of relative permeability, rock thermal conductivity, heat losses, API gravity of oil, initial conditions, oxygen concentration, and other parameters on fuel availability and combustion front velocity. Results from simulation studies show that oil viscosity, residual oil saturation (gas/oil system) and oxygen mole fraction in the injected gas should have the greatest effect on fuel availability. Relative permeability data and rock thermal conductivity also affect the amount of fuel available for combustion. Factors which may cause an increase in combustion front velocity may also cause an increase in the amount of fuel burned if the heat front moves slower than the combustion front. The use of a thermal simulator for this study made it possible to study a wide range of parameters which would involve a substantial effort to investigate experimentally.

Summary A laboratory study was designed to improve fluid displacement efficiency in porous media by an in-situ foaming process and to determine the effect of mixed surfactant chain length on surface properties of foaming solutions, bubble size, breakthrough time, and fluid displacement in porous media. We screened various mixed surfactant systems, such as sodium dodecyl sulfate and alkyl alcohols. Maximum breakthrough time and fluid displacement efficiency were observed when both components of the mixed foaming system possessed the same chain length. Results were compared with data obtained using water, brine, and sodium dodecyl sulfate alone. The microscopic studies revealed that the order of bubble size measured outside the porous medium for various mixed surfactants was indeed maintained in a micromodel. The increase in the porous medium length improved breakthrough time and fluid displacement efficiency in sandpacks and in Berea cores. Mixed surfactant systems showed a correlation among surface properties of foaming solutions, bubble size, break-through time, and fluid displacement efficiency in a porous medium. Maximum foaminess, minimum bubble size, minimum surface tension, maximum surface viscosity, maximum breakthrough time, and maximum fluid displacement efficiency were observed when the two components of the surfactant system had the same chain length.

Summary This paper discusses tracer flow in layered reservoirs. Analytic expressions are presented describing tracer breakthrough curves from layered systems at unity mobility ratio, including rigorous treatment of tracer mixing phenomena. A nonlinear Optimization technique is introduced to analyze tracer profiles from layered reservoirs (the inversion problem). The optimization profiles from layered reservoirs (the inversion problem). The optimization algorithm generates porosity-thickness and permeability-thickness products for each layer. Also included is a field example illustrating the application of this method. Introduction Prior knowledge of reservoir heterogeneity is important in the design and Prior knowledge of reservoir heterogeneity is important in the design and operation of EOR projects. In any fluid injection operation, the high- permeability streaks receive substantial quantities of the injected fluid. permeability streaks receive substantial quantities of the injected fluid. This disproportionate distribution of the injected fluids reduces the volumetric sweep efficiency of the reservoir and hence lowers the process efficiency. Therefore, detection of the high-permeability zones and channels would be helpful in understanding and increasing the efficiency of injection projects. A means of tracking fluid movement in a reservoir is an important tool in directly determining reservoir heterogeneities. Radioactive and chemical tracers provide the capability of achieving this purpose. Well-to-well tracer breakthrough profiles can furnish information about the nature of reservoir layering. Often these tracer breakthrough profiles are a summation of tracer responses from several layers that constitute the formation. In practice, the number of the layers is unknown and only the tracer breakthrough curve from the multilayered system is available. This is a classic inversion problem. To analyze any of these combined tracer breakthrough profiles, they must be deconvolved into their individual layer responses. From the layer responses it is possible to compute important parameters of the layers, such as permeability- and porosity-thickness. parameters of the layers, such as permeability- and porosity-thickness. To perform the deconvolution, it is necessary to describe mathematically the tracer breakthrough curves from single-layer homogeneous systems as accurately as possible. Several works have been published on theoretical computation of tracer breakthrough curves. However, each of these includes approximations, which produce inaccurate definitions of tracer breakthrough profiles. Furthermore, only the fully developed five-spot patterns have been considered. For this work, exact analytic solutions have been derived that describe the tracer breakthrough curves from the five-spot pattern as well as several other common flooding patterns. In addition, it was necessary to derive exact expressions for the pattern breakthrough curves (displacing fluid cut vs. PV injected in immiscible displacements) of these same systems at mobility ratio of unity. These curves have been correlated into a single curve using a simple correlating parameter called "dimensionless PV." This paper presents a brief review of mathematical descriptions of PV." This paper presents a brief review of mathematical descriptions of tracer breakthrough curves along with the pattern breakthrough curves of several homogeneous developed patterns. An optimization technique is presented that generates the equivalent layering of the system. The presented that generates the equivalent layering of the system. The technique has been applied to analyze a tracer effluent profile from a field five-spot system. Mixing Theory Miscible fluids in a porous medium are subject to convection and dispersion. Convection is the bulk movement of fluids caused by injection and production. Dispersion results from the movement of individual fluid particles, which travel at variable velocities through the tortuous pore particles, which travel at variable velocities through the tortuous pore channels of the porous medium. As a result of this irregular movement, a transition zone (or a mixed region) forms between two miscible fluids. The size of this zone is controlled by the dispersive characteristic of the porous medium. Generally, hydrodynamic dispersion occurs in two porous medium. Generally, hydrodynamic dispersion occurs in two directions - along the mean flow (longitudinal dispersion) and perpendicular to direction of mean flow (transverse dispersion). For perpendicular to direction of mean flow (transverse dispersion). For practical purposes, transverse dispersion has little effect on the amount practical purposes, transverse dispersion has little effect on the amount of mixing between fluids. Hydrodynamic dispersion is not the only source of mixing. Molecular diffusion occurring in each pore along and across each streamline also contributes. However, it has been shown that the effect of molecular diffusion is negligible unless displacement is occurring at very low velocities. Therefore, longitudinal hydrodynamic dispersion is the major factor in establishing the mixed zone between miscible fluids flowing in porous media. porous media. The concentration of each fluid in the mixed zone can be computed as a function of position if the dispersive property of the porous medium is known. JPT p. 1753

Abstract A study was made of the method for determination of swept volume and the proper average temperature to use for interpretation of combustion falloff data using the "pseudo-steady" state concept. Two thermal simulators were used for this study to include non-uniform reservoir temperature and variable saturation effects. Skin and storage effects were not included. Interpretation of the data was based on the finding that, because of the very large contrast between the conductivity of gas in the swept volume and that in the unswept sand ahead, transient effects caused by the swept volume would be characteristic of a section of very high transmissivity (kh/w). This implied that the transition period characteristics of the falloff data will form a straight Cartesian line whose slope will be related Lo the swept volume. This follows from the concept of "pseudo-steady" state. Results obtained from the analysis of simulated data showed good agreement between calculated swept volume and actual swept volume. However, the swept volume was found to include both the burned volume and also the high gas saturation zone ahead of the combustion front. Thus a volume correction is necessary to relate the swept volume to the burned volume. In addition, average temperatures within the swept volume were calculated so that the appropriate physical properties can be included in the interpretation. properties can be included in the interpretation. Graphs which can he used to make these corrections are presented for use in interpreting similar field falloff data. Although a one-dimensional radial model was used for this study, the concept should apply in multi-dimensional cases where gravity override is common. Introduction Many authors have applied different methods to estimate the swept or burned volume from pressure falloff analysis. These methods include pressure falloff analysis. These methods include the radius of investigation method, the semilog intersection method, the deviation time method and material balance methods. Some of these methods yield swept volume that is larger than the actual swept volume. Recently, there has been interest in using the "pseudo-steady" state concept, a material balance method, in the analysis of thermal falloff data. Due to the large contrast between the mobility of the gas in the swept volume and the fluid in the unswept sand ahead of the front, the swept sand tends to behave like a large tank closed except at the well. This phenomenon has been observed by Mangold et al in their study of geothermal reservoirs. They observed that the presence of zones of different temperatures in presence of zones of different temperatures in non-isothermal reservoirs, resulted in a fluid mobility contrast that may resemble permeability barriers during well testing. The use of this concept has been investigated with different models. The results show that a typical pressure falloff curve will normally consist of an initial semilog straight line followed by a transition period and finally by a second semilog straight line. The transition period may contain a straight Cartesian line whose slope is related to the swept volume. In the models used in these investigations, several assumptions were made. These include; that the reservoir temperature is uniform, no saturation gradient exists at the front, the gas in the swept volume behaves as fluid of slight but constant compressibility, and the front interface is an isopotential surface. This study used finite difference thermal simulators to relax some of the assumptions, and to evaluate the appropriate temperature to be used in the analysis of combustion falloff data. Also the swept volume as determined from pressure analysis was compared with the actual simulated volume. THEORY The slopes from the initial semilog straight line and the Cartesian straight lines are related to the reservoir and fluid properties by the following equations: (1) P. 205

Abstract A practical procedure is presented for determining the radius of the thawed-permafrost region around a well and finding the temperature distribution in that region. Such information is important in drilling, completion, and production operations in Arctic regions. A new numerical method was developed and used in a computer model to generate solutions for radial thawing of permafrost with axial symmetry, which was shown to be a function of three dimensionless parameters plus dimensionless radius and time. The model generated solutions for the range of values of the three parameters for conditions in Alaska's North Slope. The dimensionless radius of the thawed-permafrost region was related to dimensionless time through a simple power-law equation containing two constants. Results generated by the computer model were used to develop correlations giving the relationships between the two constants and the three parameters. The correlations can be used to find the thawed-permafrost radius, and once this information is available, the temperature distribution in the thawed region can also be calculated. For the correlations, the temperature at the well was assumed to be constant. In more realistic situations in which well temperature varies with time, we also describe a simple method of calculating the amount of thawing.