Introduction

Natural gas reservoirs produce hydrocarbons that exist primarily in the gaseous phase at reservoir conditions. To predict the gas production rate from these reservoirs, there is a need to review some of the fundamental properties of hydrocarbon gases. This is particularly important (more so than in the case of oil reservoirs) because certain physical properties of gases and gas mixtures vary significantly with pressure, temperature, and gas composition. Following is a brief review of gas gravity, the real gas law, gas compressibility, the impact of nonhydrocarbon gases, gas viscosity, and gas isothermal compressibility.