Answer :
Capillary pressure refers to the difference in pressure across the interface between two immiscible fluids in a reservoir. There are two types of capillarity: spontaneous imbibition and forced displacement.
Capillary pressure is the pressure difference between two immiscible fluids, such as oil and water, in a porous medium. It arises due to the interfacial tension between the fluids, the contact angle at the fluid interface, and the size of the capillary tubes within the porous medium. The capillary pressure can be calculated using the Young-Laplace equation, which relates the capillary pressure to the interfacial tension, contact angle, and capillary tube radius.
There are two types of capillarity: spontaneous imbibition and forced displacement. Spontaneous imbibition occurs when a wetting fluid displaces a non-wetting fluid in a porous medium due to capillary forces. Forced displacement, on the other hand, involves injecting a fluid into a porous medium to displace another fluid.
Capillary hysteresis refers to the variation in capillary pressure during drainage (when the wetting fluid is being displaced) and imbibition (when the wetting fluid is being absorbed). This hysteresis is caused by the trapping of non-wetting fluids in the porous medium, leading to a difference in capillary pressure depending on the direction of fluid flow.
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