Gravitational Drainage of Liquids from Unconsolidated Wilcox Sand

Abstract

Abstract A marked gravitational segregation of liquid has been observed to take placein a number of volumetric fields toward the later stages of their oil-producingperiods. This phenomenon has been pronounced in thick, highly permeable sandformations such as those of the Wilcox zone in Oklahoma City. This observationhas prompted considerable research directed toward the semiquantitativedetermination of the equilibrium saturation distribution of oil verticallythroughout a formation at final depletion. In this paper, data are alsopresented showing the transient distribution of liquid at different stages ofthe depletion period. Other experimental results show the effect of temperatureon the drainage rates of water, Wilcox crude oil, and a close-cut heptanefraction. Intermittent drainage of liquid produced saturation gradients thatmight well be expected from the flow theories involved. Yields of the variousliquids varied from 50 to 75 per cent of the original fluid content of thesand-packed (4 in. by 8 ft.) vertical tube. Introduction In certain volumetric oil fields the performance of the reservoir during thelatter part of its producing life is governed to a large extent by the downwardmovement of liquid due to the force of gravity. This is especially true offormations having thick or tilting beds of uniformly high permeability, free ofshale breaks. Leverett and Katz have presented original data and discussed thetheory relating to the capillary and gravitational forces acting on liquidscontained in a sand body. These investigators have pointed out the importanceof such studies in the estimation of future reserves as well as the originalfluid content of a reservoir. In this previous work, no data have been reported showing the history ofsaturation distributions during the drainage period. Since a knowledge of thesetransients is helpful in obtaining crude oil from such a reservoir, the authorshave obtained these data during this investigation. T.P. 1548