TABLE OF CONTENTS Reservoirs containing only free gas are termed gas reservoirs. Such a reservoir contains a mixture of hydrocarbons, which exists wholly in the gaseous state. The mixture may be a dry, wet, or condensate gas, depending on the composition of the gas, along with the pressure and temperature at which the accumulation exists.
Gas reservoirs may have water influx from a contiguous water-bearing portion of the formation or may be volumetric (i.e., have no water influx).
Most gas engineering calculations involve the use of gas formation volume factor B g and gas expansion factor E g. Both factors are defined in Chapter 2 by Equations 2-52 through 2-56. Those equations are summarized below for convenience:
Gas formation volumxe factor B g is defined is defined as the actual volume occupied by n moles of gas at a specified pressure and temperature, divided by the volume occupied by the same amount of gas at standard conditions. Applying the real gas equation-of-state to both conditions gives:
The gas expansion factor is simply the reciprocal of B g, or:
where B g = gas formation volume factor, ft 3/scf
E g = gas expansion factor, scf/ft 3
This chapter presents two approaches for estimating initial gas in place G, gas reserves, and the gas recovery for volumetric and water-drive mechanisms:
Volumetric method
Material balance approach
Data used to estimate the gas-bearing reservoir PV include, but are not limited to, well logs,...
