In porous media, there are a variety of configurations in which threeimmiscible fluids can be distributed within a single body. For example, thefluids may be distributed as concentric rings. Alternatively, two fluids may bedispersed as separate blobs within the third fluid. The configuration governsthe mobility of each fluid, and under equilibrium conditions is dictated by thethree phase capillary pressure of the system. If the capillary pressure isaltered, the configuration will change. Capillary pressure can be altered byflow of any phase through the pore body. However, in a three phase system flowcannot be described as simply "drainage" or "imbibition ". Rather, flow must bedescribed as "drainage / drainage ". "drainage / imbibition" or "imbibition /imbibition " to account for the change in saturation of all three phases. Thispaper elaborates on the issues governing three phase capillary pressures andpresents some first experimental results on oil/water/gas capillary pressuresin a drainage / drainage mode.

Literature Review

Three phase capillary pressure data were first presented in a ternary plotformat by Leverett 1. Details of how the data were obtained were notdiscussed. Another effort to present quantitative information on three phasecapillary pressure systems was recently initiated in the field ofhydrology.

Lenhard and Parker 2 developed an experimental apparatus to directlymeasure monotonic capillary pressure curves for water/oil/air systems inunconsolidated media. Treated ceramic disks were used to create semi-permeablemembranes for the free flow of water and oil from different ports. Directmeasurements of water and total liquid saturations in three phase systems asfunctions of oil/water and air/oil capillary heads, respectively, were comparedto saturation-pressure measurements in two-phase air/oil and oil/water systemsfor monotonic drainage saturation paths. Excellent agreement was observedbetween total (liquid saturations in an air/oil/water system and oilsaturations in an airfoil system as functions of air/oil capillary head.Excellent agreement was also found between water saturations in air/oil/waterand oil/water fluid systems versus oil/water capillary head.

The concept of three phase capillary pressures in enhanced oil recovery wasrecently revisited by Kantzas et al.3,4 and Chatzis et al.5. Three phase interactions (water/oil/gas) were investigated In thecourse of investigating gravity assisted immiscible gas injection (GAIGI).Three phase capillary interactions were studied usually in regular geometrypores, but were not quantified.

This was done by Kalaydjian 6 who performed both drainage andimbibition capillary pressure measurements using a multi porous membraneapparatus. Clashach sandstone cores were used Measurements showed that othdrainage and imbibition cores depend on the three saturations. This conclusioncontradicts the results of Leverett as well as the hydrology models presented Earlier.

Kalaydjian 6 and Kalaydjian and Tixier 7demonstrated theeffect of the spreading coefficient on drainage capillary pressures (gas/oil)in the presence of connate water. It was found that the residual oil saturationwas lower in the case of positive spreading coefficient than in the case of anegative one. Except for the low saturation values, the capillary pressure washigher than the case of a positive spreading coefficient than in the case of anegative one.

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