Introduction
Reservoir fluids can exist as a liquid (oil) phase, a gas phase, or both phases together.
Some of the basic definitions are shown below.
Petroleum
Petroleum is a complex mixture consisting of predominately hydrocarbons and impurities such as sulphur, nitrogen, oxygen, and even helium. The physical properties of crude oils vary considerably, and are dependent upon the concentration of the various hydrocarbons.
Liquid
McCain [1990] defines gas as a homogenous fluid with low density and viscosity. The fluid does not have a specific shape or volume but it expands itself to totally fill any container shape. McCain also explains that because gas molecules are much further apart than liquid molecules, gas properties differ considerably from liquid properties. Therefore, any change of any of its state (i.e., pressure, temperature) results in a much greater effect on gas properties, than liquid properties.
Gas
Generally, gas is state of matter that has no fixed shape and no fixed volume. Gases have a lower density than other states of matte r , such as solids and liquids. Relative to other states of matter, there is a great deal of empty space between particles. In hydrocarbon scenarios, natural gas is predominately methane and lighter hydrocarbons.
See Also: