ABSTRACT

Based on a very large data set from more than 20 petroliferous basins throughout the world, a new conceptional model and associated technologies for exploring unconventional basin center gas accumulations have been developed by the Institute for Energy Research (IER) at the University of Wyoming. The key technologies involve:

• Determining the position of the boundary between normal and anomalous pressure regimes;

• Evaluating the two- and three-dimensional aspects of this pressure boundary surface; and

• Detecting and delineating those sections with the greatest potential for enhanced storage capacity and deliverability (i.e., "sweet spots") below the pressure boundary surface using one-, two-, and three-dimensional velocity modeling and visualizations of well log and seismic data.

The concepts leading to the development of these technologies are detailed in numerous papers and GRI reports, including (among others) the following: Surdam et al., 1996; Surdam etal., 1997; Heasler et al., 1995; Jiao and Surdam, 1993; and Jiao, 1992. From these works, it is clear that (1) in Laramide foreland basins, the pressure boundary surface is associated with a significant sonic velocity inversion, which coincides with marked changes in clay diagenesis, kerogen structure, vitrinite reflectance, production index, and the displacement pressure and sealing capacity of the Cretaceous shales; and (2) rock volumes with significantly low velocity below the pressure surface boundary are generally saturated with gas. Thus, the pressure boundary surface and gas accumulations below this surface can be detected and delineated using the sonic velocity analysis and advanced 3D visualization techniques developed by IER. In the present paper, we use the Washakie Basin of Wyoming as a test basin for these technologies.