Steady Flow of Gas-oil-water Mixtures through Unconsolidated Sands

Abstract

The dynamic behavior of a multiple fluid system is completely describable interms of driving forces and resistances to flow. The latter are proportional tothe viscosity of the fluid under consideration and inversely proportional to aproperty of the system termed the" effective permeability" to thatfluid, a property therefore defined by this relation. Since three phases are usually present in oil reservoirs, it is essential toknow the effective permeabilities to the several fluid phases, and therelationship between the composition of the fluid in the pore space and that ofthe flowing stream, in order to handle satisfactorily certain problems of oilproduction. In this regard, there are many unknown factors and parameters, andmany that can be evaluated only indirectly. However, it is expected that workalong lines similar to this present undertaking will help materially in solvingthese problems. Previous workers in this field have investigated the two-phase systems, water-gas, water-oil in unconsolidated sands, and water-gas in consolidatedsands. The extension of the study of the flow of heterogeneous fluid systemsfrom two to three phases involved only slight changes in technique. Theapparatus used in the present work, except for slight changes to be described, was that used by Leverett in his water-oil experiments. Correlation andinterpretation of data were made by methods analogous to those used in two-phase work. The relative permeability to a phase-the effective permeabilitydivided by the permeability of the system to a homogeneous fluid-was employedthroughout in correlating the rate of flow of that phase with the compositionof the pore space. Quantitative measurements of two independent physical properties of the systemwere required to determine the composition of the pore space. As in thetwo-phase work, the fraction of water was determined electrically. The gasfraction was determined by measuring changes in volume accompanying measuredpressure changes. Suitable account was taken of the solubility of the gas inthe liquid phases, and of the vapor pressure of the water phase. Since thiswork was exploratory in nature, no attempt was made to obtain highly accuratenumerical results. Reasonable precision and reproducibility were sought. Experimental Procedure Variables Considered.-Of the properties of the fluids, the oil viscosity ismost likely in practice to vary widely. Variations in oil viscosity weretherefore included in this work, but variations in other properties of thefluids are as yet unexplored. It appears unlikely that the normally encounteredvariations will produce significant changes. The observations were made atfairly high pressure gradients, no attempt being made to detect a variation ofthe relative permeabilities with pressure gradient. T.P. 1206