Explain how produced gas measurements are used to compute gas production rate, and how flow meters account for gas compressibility.

• A. Gas rate is measured by flow meters or differential pressure across a separator; compressibility accounted for by expansion factor Y and gas property corrections; rate expressed in standard conditions.
• B. Gas rate is derived from crude oil production rates and adjusted for density.
• C. Gas rate does not account for compressibility and is always in actual field conditions.
• D. Gas rate is measured only by temperature.

Answer: (A)

The main idea is that gas production rate is found from the actual flow measured at surface conditions and then converted to standard conditions to account for gas compressibility. Surface flow meters or the differential pressure across a separator provide the raw gas flow at operating conditions. Because natural gas is compressible, its volume expands as pressure drops, so the measured volume must be corrected to a standard reference. This is done with the expansion factor Y and gas-property corrections (such as Z and composition corrections), transforming the rate into standard-volume terms (for example, standard cubic feet per day). Expressing the rate in standard conditions allows consistent comparison and reporting across wells and time, despite varying pressure and temperature.

Other approaches that rely on oil production rates or ignore compressibility, or that use only temperature, don’t capture the true gas flow behavior or provide comparable standard-volume rates.