Microscopic Mechanism of Multiphase Fluids Flowing Through Rocks

In general, it is rare that there is only one phase fluid in hydrocarbon reservoir. Petroleum reservoirs contain at least two fluid phases in the porous rock: either oil and water or gas and water. In most cases, two-phase or multiphase immiscible fluids, such as oil and water, or gas and water, or oil, gas and water, coexist in reservoir.