Abstract: Disclosed are methods, systems, and computer-readable medium to perform operations including generating a material balance plot for a plurality of wells in a gas reservoir. The material balance plot includes, for each of the plurality of wells, respective static pressure/compressibility factor (P/Z) values plotted against cumulative production in the gas reservoir. The operations further include calculating, for each of the plurality of wells, a respective slope of the respective P/Z values plotted against cumulative production. Also, the operations include grouping, based on the respective slopes and locations of the plurality of wells, each well into a respective cluster. Additionally, the operations include designating each respective cluster as a separate compartment in the gas reservoir.