Which of the following best represents capillary pressure?

Which of the following best represents capillary pressure?

• A. Non-wetting and wetting phase pressures
• B. Pore pressure
• C. Hydrostatic pressure
• D. Capillary interface pressure difference

Answer: (A)

Capillary pressure is the pressure difference between the two immiscible fluids occupying the pore space, arising from the curvature of the interface and interfacial tension. It is defined as the pressure in the non-wetting phase minus the pressure in the wetting phase (Pc = P_nw − P_wet). This direct difference between the two phase pressures best captures what capillary pressure represents in a pore, since it tells you how much one phase is pressurized relative to the other within the same pore. Pore pressure describes the overall fluid pressure in the pore space, not the differential between phases. Hydrostatic pressure is the vertical pressure variation due to gravity. The phrase capillary interface pressure difference is basically describing the same idea, but the most explicit and commonly used representation is the difference between the non-wetting and wetting phase pressures.

Capillary pressure is the pressure difference between the two immiscible fluids occupying the pore space, arising from the curvature of the interface and interfacial tension. It is defined as the pressure in the non-wetting phase minus the pressure in the wetting phase (Pc = P_nw − P_wet). This direct difference between the two phase pressures best captures what capillary pressure represents in a pore, since it tells you how much one phase is pressurized relative to the other within the same pore.

Pore pressure describes the overall fluid pressure in the pore space, not the differential between phases. Hydrostatic pressure is the vertical pressure variation due to gravity. The phrase capillary interface pressure difference is basically describing the same idea, but the most explicit and commonly used representation is the difference between the non-wetting and wetting phase pressures.