High Resolution Geophysical Imaging of Middle Ordovician Fault-Controlled Dolostone, Central Kentucky

Reid, William F.¹, James A. Drahovzal², David C. Harris², and Woolery, E. W.^3
1 Department of Geological Sciences, University of Kentucky, Lexington, KY
² Kentucky Geological Survey, University of Kentucky, Lexington, KY
³ Department of Geological Sciences, University of Kentucky, Lexington, KY

Fault-controlled dolostone bodies are exposed in Ordovician outcrops in central Kentucky, and are analogs to subsurface hydrothermal dolomite hydrocarbon reservoirs in the Trenton-Black River interval of the Appalachian Basin. Shallow, high-resolution P and SH-wave seismic data were acquired over two of these bodies to better characterize the subsurface extent of the dolomitization, and to identify locations for core drilling. The P-and SH-wave reflection data were collected with a 48-channel engineering seismograph. Preliminary work was performed to evaluate acquisition parameters; the results suggested that two inline spreads of 24 40-Hz P-wave, and 24, 30-Hz, horizontally-polarized geophones with spaced at 4 m (P-wave) and 2 m (SH-wave) was optimal. The energy source used was a section of steel H-pile struck horizontally with a 1.4 kg hammer. The steel H-pile had hold-down weight of approximately 70 to 80 kg, including the weight of the hammer swinger. The flanges of the H-pile are placed in slit trenches and struck perpendicular to the geophone spread for SH-mode generation. A conventional shallow CDP processing sequence was applied to the data. Front-end and surgical mutes were given special attention to ensure that coherent noise was not inadvertently stacked. Results to date have resolved previously unrecognized structures in the subsurface, such as folds, faults, and anticline/syncline structures. The data show reflector lows where dolostone may be present in the subsurface, but future geophysical modeling will be needed to delineate the limestone/dolostone interface.

AAPG Search and Discovery Article #90031©2004 AAPG Eastern Section Meeting, Columbus, Ohio, October 3-5, 2004