Relative Permeability and Low Tension Fluid Flow in Gas Condensate Systems

Abstract

ABSTRACT This paper summarises the results of an experimental study on fluid flow and residual saturations in a methane-propane gas condensate fluid system. Significant reduction in residual saturation and much improved flow rates are observed below a critical value of IFT (0.05mNm−1). At IFT values greater than 0.05mNm−1 phase distribution in the porous media is maintained through a balance in capillary and gravitational forces. The symmetry is, however, destroyed below 0.05mNm−1 when capillary forces become negligible and a first order transition in phase distribution takes place. Now, gravitational forces become important and the Bond Number more appropriate in interpreting the data. The micromodel work of Williams and Dawe, and Danesh et al established that under these conditions the liquid exists as a thin film along the grains while the gas occupies the centre of the pores, that is, a complete wetting situation. The absence of hysteresis effects in relative permeability curves confirm these observations. Under low IFT conditions, the liquid phase flows more easily, probably by a mechanism similar to that of gravity flow in hydrology studies, that is, as ‘free surface’. Here, the liquid surface is considered as a ‘stream line’ and flows when it intersects a ‘surface of seepage’. This could account for the phase separation caused by gravity often referred to as ‘gravity segregation’ and which generally occurs at conditions close to the dew line pressure.