Original gas in place estimations for geopressured gas reservoirs

Estimating the original gas in place (OGIP) of high-pressure, ultra-high pressure, and fractured stress-sensitive gas reservoirs has always been challenging. This chapter focuses on 22 different methods for OGIP calculation based on the material balance equation combined with gas field examples, which generally fall into five categories, namely, classical slope two-segment analysis method, linear regression analysis method, nonlinear regression analysis method, type curve matching, and trial-and-error analysis method. In addition, the process and recommendations for OGIP estimation of high-pressure gas reservoirs are introduced.