In Lesson 3, we discussed basic Rock, Fluid, and Rock-Fluid Interaction properties; while in Lesson 4, we applied these properties to oil reservoirs. In this lesson, we will discuss how these properties are used by reservoir engineers working on gas reservoirs.
The tasks for reservoir engineers working on gas wells or gas fields are much the same as the tasks involved for oilfields: the estimation of the original gas-in-place, OGIP, and the estimation of the rates and volumes of fluids produced from the production wells and from the field. For in-place fluid calculations, the Volumetric Method and the Material Balance Method are just as applicable for gas reservoirs as they are for oil reservoirs. We will see, however, that there are differences in the forms of the equations due to the compressible nature of gas. In addition, we will see that the stabilized Inflow Performance Relationships, IPR, (boundary dominated well production rates from Darcy’s Law) and the time dependent diffusivity equation are also impacted by the compressible nature of the gas.