Mathematical Modelling of Condensate Film Flow by Gravity Drainage

High pressure micromodel experiments at Heriot-Watt University on gas-condensate systems have demonstrated that at low values of interfacial tension the gravity force is dominant and the condensate that is formed just below the dew point pressure, flows in the form of a film on the surfaces of pores and connate water. This paper presents mathematical modelling of such a film flow process within a pore with an idealised and well defined geometry. The pore is assumed to have its sides defined by a parabolic equation. Water resides in the corners. New equations have been derived and computer programs have been written to calculate the capillary pressure- water saturation relationship and the relative permeability of condensate as a function of condensate saturation and pore geometry for the film flow process. The effects of variations in pore geometry water saturation and the fluid properties on capillary pressure and relative permeability have been investigated. Higher values of water saturation result in higher relative permeability to condensate. Condensate relative permeability is found to be sensitive to its viscosity particularly at low values of viscosity; with lower viscosity producing higher relative permeability. The results indicate that condensate relative permeability will be very low, ca 1% at condensate saturation of about 10%. This can nevertheless be important for gravity drainage in the main body of the reservoir.