Revaporization of Butane and Pentane from Sand

Abstract

Abstract A study of the behavior of retrograde condensation from gas mixtures wasmade in the presence and absence of sand in order to determine if the condensedliquid would revaporize in the presence of sand. Methane-butane andmethane-pentane mixtures that would form liquids by retrograde condensationwhen produced from a constant volume cell were used. The methane-butane mixtures of similar composition were produced by threedifferent methods. The first two were charged into an empty cell and wereproduced in one case within a period of 9 hr and in the other within a periodof 3 days. The third mixture was charged to a sand-packed cell and producedwithin a period of 9 hr. The curves relating composition of the produced gas topressure obtained from these experiments show that equilibrium was maintainedas long as liquid was condensing. However, during the portion of the pressuredecline where the condensed liquid should be revaporizing, equilibrium wasmaintained only when the mixture was produced from the sand-packed cell. The methane-pentane mixture is produced only in the presence of sand. Thedata obtained for this system also show that equilibrium is maintained at alltimes during the pressure decline. These results indicate that revaporization is aided rather than prevented bythe fact that the condensate" wets the sand." Introduction The significance to the petroleum industry of the behavior of hydrocarbonsin the retrograde region is becoming increasingly important because a largepercentage of reservoirs being discovered today are of the gas-condensate type.The important characteristic of a gas-condensate reservoir is the retrogradecondensation of a liquid phase throughout the reservoir if the pressure isallowed to decline. In order to prevent the loss of this retrograde liquid insome of these reservoirs, they are "cycled"; that is, the materialproduced from the reservoir is processed to remove the heavier hydrocarbons andthe light fractions are returned to the reservoir to maintain the reservoirpressure. Another method of producing these reservoirs is pressure depletion.There are other methods but they are not in general use. Although a large number of factors are involved in determining the optimummethod of producing a reservoir, only the problem of whether the retrogradecondensate resulting from pressure depletion will revaporize from sand atequilibrium conditions is considered in this paper. Also the data are limitedto the methane-n-butane and the methane-n-pentane systems at 100'F and one typeof sand. Three types of tests were run in order to compare the revaporization ofretrograde liquid formed in a cell with that formed in a sand-packed cell, andto establish the effect of time. T.P. 2467