Some Features of Capillary - Gravity Equilibrium in Layered Strata

Sometimes common determination of water/oil contact in a reservoir is not a trivial objective. For instance interpretation of logging data for Umenskoe oil field gave the anomalous distribution of oil saturation in J2 reservoir. The middle part of the reservoir between 22 and 50 m has the largest value of oil saturation. The reservoir is significantly heterogeneous, the averaged depth distribution of water saturation and permeability are presented on the fig. 1. The highest oil saturation correlates with a middle permeability of the reservoir. That is why the analysis of capillary-gravity equilibrium in layered reservoir was performed. The equilibrium condition is characterized by fluids immobility and leads to the equation for pressures definitions [2, 5]: (1)Po-Pw=pc=(ρw-ρo)gz+Const where Po, Pw - are water and oil pressures, pc - capillary pressure drop, g - gravity constant, z - vertical coordinate, pv, po - water and oil densities. Capillary pressure drop is defined through the dimensionless Leveret function [3]: (2)pc=J(S)σcosθk/m where σ - is the interfacial tension coefficient, Θ- wetting angle, к - permeability, m - porosity, J(S) - Leverett function; S - water saturation. In the equation (2) the expression in the denominator determines the averaged pore radius. All laboratory results on capillary pressure investigations (there were seven experiments) were processed to determine a Leveret function. The final results are given on the fig.2. As it is shown the classic presentation of capillary functions is a reliable techniques, there was only one correction: the index in denominator is slightly less than 0.5. й взгляд, распределениям водонасыщенности в пласте.