Joint Meeting: University of Wyoming Department of Geology and Geophysics Wyoming Geological Association Geological Survey of Wyoming: April 2-4, 1982 Laramie, Wyoming: Subsurface Practices in Geology and Geophysics Abstracts of Papers - Compiled by James R. Steidtmann

A high-resolution seismic survey was conducted at the Laramie Energy Technology Center’s underground coal gasification test site near Hanna, Wyoming. The objectives of the project were two fold: first, to investigate the feasibility of utilizing high-resolution seismic technology to locate and characterize underground coal gasification zones; and second, to locate shallow faults in the vicinity of the experimental area at Hanna. The Hanna II, phases 2 and 3 experimental site was surveyed in detail.

Seismic data acquisition and processing parameters were specifically designed to emphasize reflections at the shallow, 200-300 ft depths of interest. A three-dimensional grid of data was obtained over the Hanna II, phases 2 and 3 burn zone. Processing included time-varying filters, deconvolution, trace compositing, and a two-dimensional areal stacking of the data in order to identify burn-zone anomalies. An anomaly was clearly discernable resulting from the rubble-collapse void in the burn zone which was studied in detail, and compared to synthetic models. An outline of the burn cavity was constructed, and this cavity shape was compared with information obtained during a post-burn drilling program.

The fault studies disclosed faults at the test site of hitherto unsuspected complexity. The fault system was found to be a graben complex with numerous antithetic faults. The antithetic faults also contain folded beds. One of the faults is located between process wells at the Hanna IV test site. A series of anomalies was discovered on the northeast end of one of the seismic lines; these reflections have been identified as underground mine adits from the Hanna No. 1 coal mine.