Hydrothermal Dolomites in the Southern Appalachian Basin: Ideal Reservoirs with Inherent Exploration Difficulties

Jonathan C. Evenick¹, Robert D. Hatcher¹, Linda C. Kah¹, Theodore C. Labotka¹, and H. Virginia Weyland^2
1 University of Tennessee, Knoxville, TN
² U.S. Department of Energy, Tulsa, OK

Hydrothermal dolomite plays have become a prominent exploration target in the Appalachian basin. Large known hydrothermal dolomite fields in the Michigan and Illinois basins (i.e., Albion-Scipio and Lima-Indiana trends) and smaller fields in the northern Appalachian basin (i.e., Glodes Corner field, NY) have illustrated that these are ideal reservoirs and petroleum targets. Consequently, interest has been growing in the southern Appalachian basin pertaining to the potential of similar hydrothermal dolomite plays. Occurrences of “light bulb or dolomite chimney structures” in eastern Kentucky and Tennessee indicate that these targets are also present within Ordovician strata, but reservoir size and quality have not been adequately addressed. Most of the documented hydrothermal dolomite structures are associated with the Rome trough fault system in Kentucky (mostly surface exposures) and subsurface Mississippi Valley type ore deposits in Tennessee (Gordonsville and Mascot-Jefferson City mining districts). Exploration and development difficulties of these reservoirs include: 1) known semi-linear structures are typically small in horizontal extent (less then 0.2 km2); 2) their small size make them difficult to delineate in the subsurface because they are below the seismic imaging resolution; 3) larger structures are represented by sagging up-section reflectors that may get confused with synclines; 4) oil is not always associated with these structures; and 5) XRD and thin-section analyses from an exposed structure suggest that secondary dolomitization increased porosity of the immediate area within and around the structure, but also produced authigenic clays (smectite) and silica, which may hinder petroleum extraction.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005