1. n. [Shale Gas]

A model of a specific volume of the subsurface that incorporates all the geologic characteristics of the reservoir. Such models are used to quantify characteristics within the subsurface volume that are relatively stable over long periods of time and can, therefore, be considered static. These attributes include the structural shape and thicknesses of the formations within the subsurface volume being modeled, their lithologies, and the porosity and permeability distributions. These last two characteristics often vary significantly from location to location within the volume, resulting in heterogeneity. However, porosity and permeability are stable in the near-geologic timeframe and do not change due to the movement of fluids or gases through any of the formations pore spaces. The result of reservoir characterization is a reservoir characterization model (also known as a static model and sometimes referred to as a geologic model). Shale gas reservoir rocks require the analysis of high-quality seismic data, core, and log measurements and engineering data to produce an accurate reservoir characterization model. This model is then used as input into reservoir simulation, during which reservoir engineers add other reservoir characteristics, such as pressures, temperatures, and fluid and gas compositions. These features can change due to the movement of fluids or gases through any of the formations pore spaces. Since these are dynamic in their nature over short timeframes, once production is initiated these models are referred to as dynamic models. Thorough reservoir simulations (dynamic models) that are based on accurately developed reservoir characterizations (static models) can be of significant value in optimizing well placement and field-development planning.