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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

The study of the flow of oil and gas mixtures through oil-bearing formationshas received special attention from the petroleum industry within the past fewyears, and has resulted in a series of research projects based upon variousphases of the flow of heterogeneous fluids through porous media. Obviously, the low cost of producing oil during the flowing life of a wellmakes it desirable to obtain production by natural flow as long as possible andto effect a maximum recovery of oil and gas by the utilization of reservoirenergy through efficient methods based upon a thorough knowledge of reservoircharacteristics. Despite the extensive research that has been carried out, there is little information available on the behavior of oil and gas mixturesflowing through reservoir formations. This makes it impossible to predeterminethe optimum operating conditions for flowing wells. A differential pressure must exist in the reservoir in order to induce flowtoward the well. It is a well established fact that with homogeneous fluids therelation of pressure drop to linear distance traveled is a straight linefunction as long as the flow is viscous. However, in regard to gas saturatedoils, a number of investigators have reported that the flow characteristics arematerially altered as some of the lighter hydrocarbons are liberated from theoil to form gas while the fluid passes through the reservoir. Most of the work done has been concerned primarily with steady-state flow ofliquid-gas mixtures cloud has studied the effects of saturating crude petroleumoils with various gases, together with the resultant pressure gradients understeady flow conditions, noting that unsaturated oils flowed faster and yetmaintained lower pressure gradients than saturated oils. T.P. 873

The data presented in connection with this investigation will serve as a guide for the engineer who plans to heat porous media on a larger scale. The experimental work gives an idea of the relative rates of heat flow through the porous material, depending on the nature of the fluid filling the pore spaces.