Ronald C. Surdam1, John Robinson2, Zunsheng Jiao1, Nicholas G. K. Boyd1
(1) University of Wyoming, Laramie, WY
(2) McMurry Energy Company, Denver, CO
ABSTRACT: Delineation of Jonah Field Using Seismic and Sonic Velocity Interpretations
Traditional exploration techniques commonly fail to detect anomalously pressured gas accumulations because these resources are not necessarily confined to conventional structural and/or stratigraphic traps. Significant reduction of the uncertainty in the search for these anomalously pressured gas accumulations can be achieved through a new exploration strategy developed by Surdam and colleagues. An important aspect of this new strategy is to isolate rock volumes characterized by anomalously slow velocities. Jonah Field in the northern Greater Green River Basin presents an important test case illustrating a successful application of this strategy.
In 1994, using velocity profiles obtained from sonic logs and 2-D seismic data, it was possible to delineate the general configuration of the Jonah Field. Interpretation of these early velocity profiles allowed exploration efforts to focus on broad regions of commercial potential. However, these early velocity profiles lacked the resolution and spatial coverage to identify specific exploration or development targets.
By 1999, velocity analysis results from high-resolution 3-D seismic data provided significantly improved detail in the delineation of the horizontal and vertical distribution of velocity anomalies in the Jonah Field. Interpretation of these velocity anomalies and integration of this information with other geophysical and geological data resulted in a vastly improved understanding of the Jonah Field's anomalously pressured gas accumulations. This new understanding, based largely on interpretation of velocity data, has led to more effective and efficient selection of exploration and development targets.
AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado