PrintTo this point in the lesson, we have discussed the origins of the reservoir rocks and traps that formed over the geologic time scale which result in modern oil and gas reservoirs. We have also discussed the origins of the hydrocarbons that reside in pore spaces of these reservoirs. We can now discuss the types of reservoirs and reservoir systems that are currently of commercial interest to the oil and gas industry. To aid in this discussion, we must first introduce the concept of the Phase Envelope (or, Phase Diagram, or Pressure-Temperature Diagram, or P-T Diagram) for single-component (pure) and multi-component (mixture) systems.