PREDICTION OF THE DEW-POINT PRESSURE OF A GAS CONDENSATE RESERVOIR
1.1 Background of study
Gas Condensate Reservoiris a reservoir having low-density mixture of liquid hydrocarbons that are present as gaseous components in the subsurface (in the reservoir). It is important to recognize that some gas condensate reservoirs show condensate dropping out within reservoirs, as well as condensate production at the surface due to pressure falling below the dew-point during production. This condensate accumulation in the reservoir initially remains immobile due to interfacial forces between it and connate water within the pores of the formation until its saturation level reaches a threshold value and becomes mobile.
Initially, the gas-condensate is totally gas in the reservoir. As reservoir pressure decreases, the gas condensate exhibits a dew-point. The dew-point of a gas condensate fluid occurs when a gas mixture containing heavy hydrocarbon is depressurized until liquid is formed, that is, a substantial amount of gas phase exists in equilibrium with an infinitesimal amount of liquid phase. A pressure is reduced; liquid condenses from the gas to form free liquid in the reservoir. Normally, there is no effective permeability to this liquid phase and it is not produced. If the pressure continues to decrease, a second dew-point will be reached and the liquid can be re-vaporized. This lower dew-point pressure is usually well below the reservoir abandonment pressure; thus it would be of no interest in reservoir performance.
By definition, dew-point pressure is simplythe pressure at which an infinitesimal amount of liquid is in equilibrium with a large quantity of gas. the pressure below which liquid condense out of the gaseous phase.