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Engineering LibreTexts

1.2: Why Study Phase Behavior?

Natural gas and crude oil are naturally occurring hydrocarbon mixtures that are found underground and at elevated conditions of pressure and temperature. They are generally referred to as petroleum fluids. Petroleum fluids are principally made up of hydrocarbons; but few non-hydrocarbon components may be present such as nitrogen, carbon dioxide and hydrogen sulfide.

We make no mistake when we refer to Natural Gas and Petroleum Engineers as Fluid Engineers. This is, engineers that deal with fluids to make a living. Moreover, we specialize in two special fluids whose importance to the society cannot be overstated--indeed, humankind rely on natural gas and crude oil as the premier source of energy that keeps the society operative. As a consequence, we may very well be titled as Hydrocarbon Fluid Engineers. That is everything we are basically about. At every stage of the oil business, a Hydrocarbon Fluid engineer is required. This is, reservoir analyses, drilling operation, production operation, processing, among others, reveal the wide spectrum of areas where an engineer with expertise on hydrocarbon fluids is fundamental.

This being said, what can be more important for a Hydrocarbon Fluid Engineer than understanding how these fluids behave?

It is not an overstatement to say that a through understanding of hydrocarbon phase behavior is quintessential for the Petroleum and Natural Gas Engineer. Phase Behavior has many implications in natural gas and petroleum engineering. Pressure, volume, temperature (PVT) relations are required in simulating reservoirs, evaluating reserves, forecasting production, designing production facilities and designing gathering and transportation systems.

Every hydrocarbon molecule in the reservoir is to embark on a fascinating journey from beneath the earth, passing through a great deal of intermediate stages, to be finally dumped into our atmosphere upon combustion (release of energy). Phase Behavior is the part of thermodynamics that gives us the tools for the complete understanding of how fluids behave at any of those stages. Let us be the witnesses of this exciting journey.


  • Prof. Michael Adewumi (The Pennsylvania State University). Some or all of the content of this module was taken from Penn State's College of Earth and Mineral Sciences' OER Initiative.