The object of this study was to determine if crude oii could be produced successfully by a process of crude oil vaporization using carbon dioxide repressuring. This process appears to have application to highly fractured fcwvnations where the major oil cotitent of the reservoir is contained in the non-fractured porosi~with little associated pertneability. Crude oil was introduced into the windowed cell and carbon dioxide was charged to the ceil at the desired pressure. A vapor space was formed above the oil, and the crude oil-carbon dioxide mixture was allowed to come to equilibrium. The vapor phase was retnoved and the vaporized oil collected as condensate. Samples of all produced and unprodttced fluids were analyzed. Tests were also performed to evaluate the amount of vaporized oil tilat can be produced by rocking from a high to a 10wer pressure. The carbon dioxide repressuring process was applied to a sand-filled cell to investigate the performance in a porous mediutn, A test was performed to evaluate how the condensate recovery changes as the size of the gas cap in contact with the oil changes.

It has been customary, in predicting saturation changes, to use the Leverett "fractional flow formula", obtained by eliminating the unknown pressure gradient from the generalized Darcy equations for the separate phases. The formula presents difficulties in the case of counterflow, since the "fractional" flow may be negative, greater than unity, or, in the case of a closed system, infinite. Recently, it has been shown by several authors that the corresponding equations (with capillary pressure and gravity terms) for actual flow of the phase may be used just as well. These equations are in agreement with Pirson's statement that, if the two mobilities differ considerably from each other in a closed system, the flow is largely governed by the lower value. The present study was undertaken because of an apparent lack of experimental data on gravity counterflow with which to test the theory. A 4-ft sandpacked tube in a vertical position was employed. Electrodes for determining saturations by resistivity were spaced along the tube, one phase being always an aqueous salt solution. Air, heptane, naphtha, or Bradford crude oil was used for the other phase. A reasonably uniform initial saturation was set up by pumping the phases through the system, after which the tube was shut in and saturation profiles obtained at definite intervals. Cumulative flows over certain horizontal levels were obtained by integration of the distributions; hence, differentiation of the cumulative flows with respect to time gave instantaneous flow rates. To compare experimental and theoretical flow values, capillary pressures were assumed given by the final saturation-distribution curve. The upper part corresponds to the "drainage" region and the lower part to the "imbibition" region, where trapping of the nonwetting phase occurred. While calculations indicated that the capillary pressure saturation function and, probably, the relative permeability saturation functions changed during the segregation, the relation of the measured rates to saturation distributions are in general accord with the frontal-advance equation. It appears that the Darcy equations, as modified for the separate phases, are generally valid for counterflow due to density differences. The usual method of predicting saturation changes, which involves a continuity equation and the elimination of the unknown pressure gradient from the flow equations, should therefore be applicable. However, the need for advance knowledge of drainage and imbibition "capillary pressures" and relative permeabilities during various stages presents difficulties. Introduction The present study was undertaken because of a seeming lack of experimental data relating to vertical counterflow of fluids of different densities in porous media. In particular, it was desired to determine whether data obtained from these laboratory tests were in accordance with certain mathematical treatments of counterflow which have been proposed. The gravity "correction" has been incorporated into the flow equations (and, hence, into displacement theory) nearly as long as both have been used. Field and laboratory data have generally borne out the validity of the theory as applied, for instance, to downward displacement by gas, with all fluids moving downward. However, the modifications for counterflow have only recently been pointed out. It has been customary to use fractional flow rates instead of actual flow rates in displacement calculations. In the case of counterflow, this results in negative values, values greater than unity and, when rates are equal and opposite, in infinite values. As pointed out by Sheldon, et al, and by Fayers and Sheldon, actual flow rates may be used just as well. The fact that these may be of opposite signs for the two fluids does not present any difficulty. SPEJ P. 185^

An apparatus was constructed for the measurement of interfacial tensions over a range of temperatures and pressures. This apparatus utilized the pendent drop method, and resembles in construction similar apparatus recently described in the literature and in use in some petroleum research laboratories. The interfacial tensions of benzene, propane, n-pentane, n-hexane, n-octane, and iso-octane against water were measured at temperature3 ranging from 26 0 to 82 0 C and at pressures ranging from 1 to 204 atm. Values of interfacial tensions for the benzene-water system and their variations with temperature and pressure are generally in good agreement with values of previous investigations.The data in all cases showed a slight decrease of interfacial tension with pressure at constant temperature in the range studied. The effect of pressure became less as the pressure was increased, with an indication of a reversal of the effect at higher pressures. There was a decrease of interfacial tension with temperature at constant pressure in all cases, as would normally be expected. This rate of decrease became greater the higher the temperature.A general equation is presented for the interfacial tensions as a function of pressure and temperature over the range lReferences given at end of paper. studied, and the constants calculated for each system. A definite trend was found in the effect of molecular weight on the interfacial tension at a given temperature and pressure, for the homologous series from propane to n-o;;tane. Data for n·decane from the literature fitted well into this trend.

Combination drive predictions by material balances require a water invasionlaw, some assumption regarding pressure decline or production rates, and asaturation equation for that part of the original reservoir which governsgas-oil ratios (unless the latter are assumed at fixed values), in addition tothe material balance. One form of the latter is the Muskat equation, which contains pressure derivatives of the volumetric fluid properties and water encroachment, the two main variables being pressure and average saturation overthe original oil zone. Another is the Tracy equation, which containspressure-dependent groups. A differential form of this equation is presented which contains pressure derivatives of the groups, and production and waterinvasion rates, with pressure and time the two main variables. Saturation equations are discussed with regard to the assumptions, particularly that ofrelease of gas in the invaded zone, this being in accordance with the material balance. The use of simple empirical equations for the various quantities issuggested. These must be of a form which give usable values for the pressureand time derivatives where required. Calculated water invasions are comparedfor various theoretical and empirical invasion formulae, with linear andexponential pressure declines. Predictions of a depletion drive by the Muskatand differential Tracy equations are compared, using various empirical relations for the required quantities. Combination performance curves are calculated by the Muskat equation for various ratios of aquifer constant topressure decline constant, both laws assumed exponential. Similar curves are calculated by the differential Tracy equation, with hyperbolic forms for waterinvasion and production rates, taking various sets of values for the constants in these forms. The calculations are programmed for a three-point Runge-Kuttamethod, taking production increments rather than pressure d4eerements where pressure stabilization or in- crease might occur. The use of such methods to optimize a production schedule is suggested.

The~.xure of petroleum engineering educzuion has been 4 subject of much concern in the last 10 years, There is no doubt that changes are needed ro keep up with the new Iools o/ technology and business, and to attract stu. dents. The planning of curricula should be governed by the definition of an engineer as a creator jor the public good and by the den-ravds oj industry, and not so much whether a department ot a degree bears /he name of a particular industry. Four-year curricula are suggested which lean toward industrial, chemical and mechanlctd engineering. The engineering student must be introduced to the new computational techniques, numerical analysis, tnathema(itxd modeling and the new approaches to decision making and problem solving. .4 2-year associate degreeprogram is suggested jor those who wish to enter lhe tech. nicai divisions oj the industry but whose inclinations do not lean toward the modern 4-year curriculum. Some comments on graduate degrees are presented.