Definition - What does Slippage mean?
Slippage is a phenomenon in which natural gas from a reservoir bypasses crude oil and water (basically liquids) that is released from the capillary openings of porous oil reservoir formations and approaches to the mean free path of the natural gas. In simple terms, slippage can also be defined as the gas movement through liquid phase of the reservoir front. This phenomenon also helps the liquid to move forward to the low pressure zones (i.e., toward the earth's surface).
Petropedia explains Slippage
When gas slippage takes place, the pressure adjustments needs to be done immediately so that the relative permeability and capillary pressure remains intact. Gas slippage is also known as Klinkenberg Gas Slippage Effect. As per this effect, the gas slippage takes place when the pore spaces approaches the natural gas mean free path.
In order to maintain the relative permeability of pores and capillary pressure during slippage, in petroleum engineering a Klinkenberg’s Correction procedure needs to be used with the help of a minipermeameter device. As per Klinkenberg, under steady flow state, the permeability of any porous media to gases is a linear function of reciprocal of mean flowing pressure which can be determined by the following equation:
Kg = Gas Permeability
q1 = Rate of Flow of gas
P1 = Injection pressure
P2 = Atmospheric pressure
ug = Viscosity of Gas
a = Internal radius of tip seal
G = Geometric factor andC = constant