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BUBBLE FORMATION in SUPERSATURATED HYDROCARBON MIXTURES Petroleum Reservoirs, the Mineral and Water Surfaces with for Each Crystal Averaging About 4.5 Sq Cm

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BUBBLE FORMATION in SUPERSATURATED HYDROCARBON MIXTURES Petroleum Reservoirs, the Mineral and Water Surfaces with for Each Crystal Averaging About 4.5 Sq Cm T.P. 3441 BUBBLE FORMATION IN SUPERSATURATED HYDRO­ CARBON MIXTURES HARVEY T. KENNEDY, A AND M COlLEGE OF TEXAS, COlLEGE STATION, TEX., MEMBER AIME, AND CHARLES R. OLSON, OHIO OIL CO., SHREVEPORT, LA., JUNIOR MEMBER AIME Downloaded from http://onepetro.org/jpt/article-pdf/4/11/271/2238408/spe-232-g.pdf by guest on 29 September 2021 ABSTRACT tude, may be calculated for any rate of pressure decline imposed on the reservoir by production. The bearing of the In many investigations of the performance of petroleum res­ number and distribution of bubbles on reservoir performance ervoirs the assumption is made that the liquid, if below its is discussed. bubble-point pressure, is at all times in equilibrium with gas_ On the other hand, observations by numerous investigators have indicated that gas-liquid systems including hydrocarbon systems, may exhibit supersaturation to the extent of many INTRODUCTION hundred psi in the laboratory. Up to the present, there has been no reliable data on which to judge the actual extent of A liquid system is supersaturated with gas when the amount supersaturation under conditions approaching those existing of gas dissolved exceeds that corresponding to equilibrium at in petroleum reservoirs. the existing pressure and temperature. The degree of super­ The work reported here deals with observations and meas­ saturation may be conveniently expressed as the difference urements on mixtures of methane and kerosene in the presence between the bubble-point of the mixture and the prevailing of silica and calcite crystals. Bubbles were observed to form pressure. Thus, if a mixture having a bubble-point of 1,000 on crystal-hydrocarbon surfaces in preference to the glass­ psi at a given temperature exists in single liquid phase at hydrocarbon interface or to the body of the liquid. Statistically, 700 psi at the same temperature, it is supersaturated to the it was found that the number of bubbles formed per second extent of 300 psi. per square centimeter of crystal surface was a function of the supersaturation only. and the function was evaluated There are many examples of high supersaturations. mostly graphically. in aqueous solutions, reported in the literature. Thus, Kenrick, Wismer and Wyatt' showed that water may be saturated with Supersaturations were observed up to 770 psi, under which oxygen, nitrogen or carbon dioxide at 100 atmospheres, and condition bubbles formed quickly and with considerable the pressure reduced to one atmosphere without producing violence. With decreasing degrees of supersaturation, the bubbles immediately. When liquids are in a state of tension. frequency of bubble formation became less, until at 30 psi they may be considered as supersaturated at least to the supersaturation and lower, no bubbles were observed to form, extent of the tension. The tensile strength of water has been even though the observation at 30 psi was continued for 138 reported as 30 atmospheres by Meyer.' 60 atmospheres by hours. It was found that silica and calcite crystals had identi­ Budgett,' 30 to 50 atmospheres by Temperley and Chambers,'" cal effects, within experimental error, in accelerating the 200 atmospheres by Dixon: and 223 atmosphere, by Briggs.' formation of bubbles, and that small amounts of water and crude oil had no effect on the results. Vincent'" determined the tensile strength of a mineral oil as It is shown that the maximum supersaturation that can exist 45 psi. Gardescu'° maintained pressures for short times in a in a reservoir may be calculated from the data presented and model reservoir at 115 psi below the bubble-point. from the area of the rock surface. It is also shown that the It should be noted that the high supersaturations observed number of bubbles formed in the reservoir, in order of magni- were obtained on systems carefully purified to remove particles 1References given at end of paper. or surfaces which might promote the formation of bubble~. Manuscript received in the Petroleum Branch office June 10, 1952. These "nuclei" were considered as contaminants which inter­ Paper presented at the Petroleum Branch Fall Meeting in Houston, Tex .• Oct. 1-8. 1952. fered with the determination of a property of the liquid. In Vol. 195, 1952 232-G PETROlEUM TRANSACTIONS, AIME 271 T.P. 3441 BUBBLE FORMATION IN SUPERSATURATED HYDROCARBON MIXTURES petroleum reservoirs, the mineral and water surfaces with for each crystal averaging about 4.5 sq cm. Sufficient kerosene WhICh 011 is in contact must be accepted as essential parts of containing no dissolved gas was introduced into the tube to the system under invetitlgation. Further, the data, to be of cover the bottom and one-half of the sides of the lowest greatest utIlity 10r engineenng purposes, should deal quanti. cry~tal. The pressure in the cell was then raised to the test tauvely with the number of bubbles formed in the reservoir preswre, usually 1,000 psi, by introducing methane, and under prevailing conditions. It is clear that observations of enough saturated kerosene was added to raise the liquid level the maximum super saturations that can be maintained for to the center of the next higher crystal, holding the pressure unspecified short periods, cannot yield this type of information. constant. In the direction of developing a quantitative approach to A valve, connecting the cell to a fixed and calibrated orifice, the phenomenon of supersaturation, it was noted that bubbles was then opened, and the pressure allowed to fall. An electric are always formed on a solid surface rather than in the liquid timer was started when the valve was opened, and the time phase. Their formation appears to be distributed at random at which the first bubble appeared was noted. In conjunction both as regards time and location on the solid surface. It with the calibration curve, the time indicated the pressure, would therefore be expected that a sufficiently large number and thus the supersaturation pressure, at which the bubble of observations would give, at a fixed supersaturation, a con­ formed. A typical calibration curve is shown in Fig. 2. Where stant average number of bubbles formed per square centimeter warranted by temperature fluctuations, corrections based on of surface per second. This theory of random formation of several calibration curves made at different room tempera­ bubbles is in accord with the wide variation of supersatura­ tures, were applied. Downloaded from http://onepetro.org/jpt/article-pdf/4/11/271/2238408/spe-232-g.pdf by guest on 29 September 2021 tions reported in the literature on apparently identical systems, and is supported by the data obtained in this investigation. The appearance of a bubble terminated a run, since con­ ~iderable mixing and evolution of gas generally accompanied its formation. To prepare for the next run, the cell was then allowed to fall to atmospheric preSHue to desaturate its EXPERIMENTAL METHOD contents. It was then again brought to the test pressure by the induction of gas, and live kerosene was added until the Methane used in this investigation was the commercial liquid level rose to the center of the next higher crystal. The material, obtained in 1,500 psi cylinders and rated as 96 per pressure was allowed to fall by opening the valve to the cent pure, the impurities being ethane, propane, nitrogen and calibrated orifice, and the observation repeatcd. After the 0 oxygen. The kerosene had an API gravity of 46.3 , with an glass tube containing the crystals was filled above the top average boiling point (10 per cent intervals) of 344°F. The crystal, the tube was emptied, and another set made. Normally, quartz and calcite minerals used were accurately cut from 8.') observations cunstituted a series, which could be analyzed large natural crystals. The crude oil used was from the East Texas Field. The choice of test methods was complicated by the fact that at high supersaturations, glass was the only solid found which did not accelerate bubble formation. In a steel observation cell, bubbles were observed to form repeatedly at certain points on the steel surface and on the exposed surfaces of the gaskets. The slightest scum on a mercury surface would promote bubble formation at high supersaturations, although no trouble from this source was observed in the lower range of values. However, at low supersaturations, due to the longer periods of observation required, the greater effect of diffusion of gas across gas-liquid boundaries eliminated the possibility of employing such surfaces. Two methods were therefore employed. In the first method, used at high supersaturations, the system was confined in a glass tube with a gas-liquid contact as an upper boundary. For lower supersaturations, the system was confined above carefully purified mercury. As will be shown later, diffusion © © was not a factor for the periods of observation required in the first method, while no bubbles were observed to form on the mercury surface in the low supersaturation tests for which the second method was used. © In both methods, filtered kerosene and methane were agi­ © tated together in an Aminco mixing bomb for several hours, at 500 psi or 1,000 psi and room temperature. An amount of gas was released that would cause a slight drop in pressure, and shaking continued. A rise in pressure to the original value © indicated that saturation was complete. The gas phase was © hIed off from the mixture at constant pressure, and the pres­ OIL AND sure then raised to 2.000 psi, to give an unsaturated solution CRYSTALS~ of accurately known bubble-point. In the first test method, used for high supersaturation values, quartz or calcite crystals were stacked in a test tube within a Penberthy visual cell as shown in Fig. 1. The crystals had rectangular faces of accurately known areas, the total area FIG.
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