| In unconventional shale gas plays, gas-in-place is a major factor in evaluating the shale's potential and determining well density and lateral placement. The two main contributors to total gas-in-place are free gas and adsorbed gas. Gas in pores, "free" gas and adsorbed gas, which equal gas-in-place when summed, contribute to production from unconventional mudstone reservoirs like the Middle Devonian Marcellus Shale in the Appalachian Basin. Gas-in-place and production volumes however, vary throughout the different areas of Marcellus production in the basin. This paper analyzes the change in volumes of adsorbed methane through the geologically different regions of Marcellus production. Comparing samples from the main production areas, two results are evident. The first is that Langmuir methane adsorption storage capacity (GSL, scf/ton) varies primarily with TOC and thermal maturity. The second observation is that other factors influence GSL such as porosity, bulk density, clay content, and resistivity. Through multiple regression analysis, a model was created to predict GSL from its most significant factors. |
