Kapillaaripainetta

Kapillaaripainetta, often translated as capillary pressure, is a fundamental concept in fluid mechanics and porous media science. It refers to the pressure difference across the interface between two immiscible fluids, such as oil and water or air and water, when they are present within a porous material. This pressure difference arises due to the surface tension of the fluids and the wettability of the porous medium.

The magnitude of capillary pressure is inversely proportional to the pore throat radius. Smaller pores generate a larger capillary pressure. This phenomenon plays a crucial role in various natural and industrial processes. In the earth sciences, capillary pressure governs the distribution of fluids in reservoir rocks, the movement of groundwater, and the behavior of soil moisture. In petroleum engineering, it is essential for understanding oil and gas recovery from reservoirs, as it influences the displacement of hydrocarbons by injected fluids.

The concept is mathematically described by the Jurin's Law, which states that the capillary pressure is proportional to the surface tension of the liquid and the cosine of the contact angle between the liquid and the solid surface, and inversely proportional to the radius of the capillary tube. In porous media, the effective pore radius is used. Capillary pressure is a key parameter in multiphase flow simulations and is determined experimentally through methods like mercury injection porosimetry or by analyzing drainage and imbibition curves. Understanding capillary pressure is vital for predicting and controlling fluid flow in a wide range of applications.