H.J. Ramey

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.

Oxidation of Crude Oil in Porous Media

Experimental results on the oxidation reaction kinetics in the forward combustion oil recovery process are presented. A total of 48 runs were made wherein a stationary thin layer of coked unconsolidated sand was burned isothermally in a combustion cell. Individual runs were made at various temperature levels to permit determination of the effect of temperature upon the reaction. An expression was obtained for the burning rate of carbon as a function of carbon concentration, combustion temperature, and oxygen partial pressure. The carbon burning rate for two types of crude oil indicated a first order reaction with respect to both carbon concentration and oxygen partial pressure. The effect of combustion temperature on the reaction rate constant matched the Arrhenius equation. The activation energy was similar for the 2 crude oils examined. The activation energy decreased for a porous media containing clay. The rate of oxidation of crude oil at reservoir temperature was found to be significant. Other significant findings included information on hydrogen-carbon content of fuel residues, fuel reactivity and the products of combustion. (17 refs.)

Non-Darcy flow in wells with finite-conductivity vertical fractures

The purpose of this paper is to provide solutions for analyzing pressure data for constant-rate wells crossed by finite-conductivity vertical fractures producing at high rates to cause non-Darcy flow effects in the fracture. The following conclusions can be drawn. 1. To describe the non-Darcy effect, two physical parameters are required: the dimensionless fracture conductivity and the dimensionless flow rate constant. 2. The effect of non-Darcy flow in the fracture is to cause an apparent fracture conductivity significantly less than the true fracture conductivity. 3. The bilinear flow period also is observed in high-rate wells that have the non-Darcy effect. Graphs of log P /SUB D/vs. log (t /SUB Dxf/) exhibit the one-fourth slope for apparent fracture conductivities less than 50. 4. Techniques used for analyzing finite-conductivity fractures also apply to the non-Darcy case, except the fracture conductivities obtained are apparent values. 5. A correlation between the flow rate constant, the true fracture conductivity, and the apparent fracture conductivity is developed in this study. 6. Two methods are presented for determining the true fracture conductivity of a well that has two sets of drawdown data obtained at two different high flow rates.

Short-time well test data interpretation in the presence of skin effect and wellbore storage

Short-time data are defined as data obtained before a conventional straight line is reached, during well testing (drawdown or buildup). Some of the factors that effect the short-time data are the effects of well-bore storage, perforations, partial penetration, and well stimulation, such as fracturing or acidizing. Although the effects of such factors are generally known, the duration and importance have not been clearly defined in all cases--particularly when these effects are combined in a well test. However, recent studies have revealed a great deal of potentially useful information concerning the analysis of short-time well test data. The purpose of this study is to illustrate the interpretation of short-time well test data through presentation of field examples. Factors to be considered include well-bore storage, well damage, and fractured wells. The log-log type-curve described shows clearly the presence of linear flow due to fracturing. It can be used to obtain quantitatively the information normally obtained from pressure buildup analyses and to identify the proper straight line in pseudoradial flow for a fractured well. (14 refs.)

The Effect of Temperature on Relative and Absolute Permeability of Sandstones

Equipment was constructed to perform dynamic displacement experiments on small core samples under conditions of elevated temperature. Oil-water flowing fraction and pressure drop were recorded continuously for calculation of both the relative permeability ratio and the individual relative permeabilities. Imbibition relative permeabilities were measured for five samples of Boise sandstone at room temperature and at 175/sup 0/F. The fluids used were distilled water and a white mineral oil. The effect of temperature on absolute permeability was investigated for six Boise sandstone samples and two Berea sandstone samples. Results for all samples were similar. The irreducible water saturation increased significantly, while the residual oil saturation decreased significantly with temperature increase. The individual relaive permeability to oil increased for all water saturations. The individual relative permeability to water decreased with temperature increase for water saturations below the room-temperature residual oil saturation, but the relative permeability to water at flood-out increased with temperature increase. Absolute permeability decreased with temperature increase.

Well Test Interpretation of Vertically Fractured Gas Wells

A mathematical model was developed to generate simulated drawdown tests for fractured gas wells. The model includes the effects of real gas properties, well bore storage, and turbulence. A special coordinate transformation is used to obtain better accuracy for turbulent flow near the well bore. The results show that the slope of the drawdown curve is affected by the nonlinearity of real gas flow.

Effect of temperature on oil/water relative permeabilities of unconsolidated and consolidated sands

Over the last 20 years, a number of studies have reported temperature effects on two-phase relative permeabilities in porous media. However, some of the reported results have been contradictory. Also, observed effects have not been explained in terms of fundamental properties known to govern two-phase flow. The purpose of this study was to attempt to isolate the fundamental properties affecting two-phase relative permeabilities at elevated temperature. Laboratory dynamic displacement relative permeability measurements were made on unconsolidated and consolidated sand cores, using water and a refined white mineral oil. Experiments were run on 2 in. (51 mm) diameter, 20 in. (510 mm) long cores from room temperature to 300/sup 0/F (149/sup 0/C). Unlike the results of previous researchers, essentially no changes with temperatures were observed in either residual saturations or relative permeability relationships. It was concluded that previous results may have been affected by viscous instabilities, capillary end-effects, and/or difficulties in maintaining material balances.

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.

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.

Well-Test Analysis for Vertically Fractured Wells

Russell and Truitt presented the transient pressure behavior of a vertically fractured well in a closed, square reservoir in 1964. They analyzed pressure buildup behavior and found that the straightline slope on a Horner-type buildup plot required significant correction as the fracture length increased. Also, they recommended a Muskat-type semi-log plot for estimation of static formation pressure. In view of the fact that over 500,000 wells have been hydraulically-fractured, it is likely that the Muskat-type plot should be used far more widely for estimation of static pressure than is actually the case. But many important points require further study. The Russell and Truitt dimensionless pressure-dimensionless time data were used to generate several hundred pressure buildup plots. Results were computer plotted such that an extreme variety of types of buildup plots (Horner, Muskat, Miller-Dyes-Hutchinson, and log-log type curves) could be studied for a wide range in length of a producing period and fracture lengths. As a results, it is possible to specify the data which will be straightened by a Muskat plot, and to estimate permeability and diffusivity from a Muskat plot. (20 refs.)