In-seam seismic logging has been utilized in coal geophysics to determine discontinuities in coal seams. However, the technique has numerous applications in various types of heterogeneous geological environments. It can be used to determine the continuity of beds between wells, estimate and locate variations in the thickness of beds, and estimate the average rock physical properties of the beds.
In this poster presentation we explain the technique of interwell seismic logging and analyze the propagation of guided waves in a fluvial sandstone formation at the Gypsy test site in Oklahoma. The study consists of an integration of the well logs, lithology, and interwell seismic data to determine the origin of the waveforms associated with specific geologic units. Selected full waveforms are correlated with the geologic units of interest, processed, and interpreted to identify trapped wave trains which may be associated with the presence of guided waves. Seismic events are extracted from the interwell seismic data using time-frequency representation techniques to analyze their propagation characteristics which can be used to identify continuity of lithology in the Gypsy sandstone.
Analysis of the data suggests the presence of a connected, low-velocity clean sandstone in the Gypsy interval. The correlation of sandstone and shale units from well logs and guided waves is consistent with crosswell connectivity mapping and pressure-pulse test data. The pressure tests indicate that the sands are in pressure communication between wells and that an impermeable barrier is present between the top and the bottom of the sand units in the Gypsy sandstone interval.