Net pay, a crucial parameter in the reservoir characterization process, is a critical input to the determination of original oil or gas in place and remaining mobile hydrocarbons.

A good definition was discussed by Cobb and Marek (1998), who deferred to the Society of Petroleum Engineers' (SPE) "Petroleum Reserve Definitions" (1997). The SPE guide defines reserves as "those quantities of oil and gas defined by an analysis of geological and engineering data that are anticipated to be economically recovered from known reservoirs from a given date forward."

This definition suggests that the hydrocarbons must not only be present but must also be able to be economically produced. Net pay is typically estimated from well log data and using core data and production data for calibration.

The purpose of this module is to determine whether each of the four samples presented qualifies as net pay. This determination will involve the calculation of effective porosity, water saturation, and permeability to hydrocarbons (gas in this example).