Systems and methods for inferring free gas production in oil and gas wells

A method of allocating produced gas to a selected well among a plurality of wells at a central facility comprising:

• for each well in the facility, inferring gas production up the annulus of the well disposed between the outer wall of tubing of the well and the inner wall of the casing of the well, comprising:
• taking a selected number of measurements during a selected period of time, each measurement including closing the annulus to allow gas pressure within the annulus to change, sampling the pressure within the annulus over a sampling time period, calculating the time rate of pressure change from samples taken over the sampling time period;
• calculating the production rate of gas in the annulus, wherein a gas volume within the annulus is an adiabatic gas volume such that the production rate of gas in the annulus is calculated using the real gas equation multiplied by k, the ratio of specific heats determined for the properties of the gas;
• and
• summing the calculated production rates for the selected number of measurements to determine an inferred rate of gas production through the annulus of the well during a selected period of time;
• for each well in the facility, determining the amount of gas produced through the tubing of the well during a selected period of time;
• for each well in the facility, determining the amount of gas used for utilitarian purposes during the selected period of time;
• for each well in the facility, determining the total gas production value during the selected period of time as the sum of the inferred production up the annulus and the determined amount of gas through the tubing less the determined amount of gas from the well used for utilitarian purposes;
• calculating an allocation factor for the selected well as the ratio of the total gas production value for the selected well described above to the sum of the total gas production values for all of the plurality of wells in the facility;
• and
• determining an allocation to the selected well as the product of the allocation factor and the total amount of gas sold from all of the plurality of wells in the facility during the selected period of time.