Possible Hydrothermal Dolomite Reservoir(s) in the Swan Creek Field, Tennessee

Bailey, Jeffrey R. ¹,  Evenick, Jonathan C. ²,. Hatcher, Robert D Jr. ²,  and Weyland, H. Virginia ³

¹Tengasco, Inc., Knoxville, Tennessee

²Department of Earth and Planetary Sciences, University of Tennessee, Knoxville

³U.S. Department of Energy, National Petroleum Technology Office, Tulsa, OK

A possible subsurface hydrothermal dolomite reservoir has recently been identified in the Swan Creek field, northeastern Tennessee.  Swan Creek field is in a blind, faulted anticline located beneath the shallow-dipping Clinchport thrust wherein small-displacement duplex imbricates partly localize production.  A structural low is superposed on the northwestern flank of an anticline that contains a pronounced increase in dolomite in the lower and middle Stones River (Black River) Group, but hydrocarbon production from surrounding wells is from the top of the Stones River (Carters Limestone).  The structural low is evident in maps contoured from top of the Lebanon Limestone downward into the Knox Group, but is not present in younger horizons.  Dolomitization probably occurred prior to Alleghanian folding and faulting, but deformation may have localized the hydrothermal zone and hydrocarbons, and did not breach and drain the reservoir.  Production probably results from secondary enhanced porosity not cemented by late-stage, pre-Alleghanian fluid migration and mineralization.  Trends in hydrothermal fluid migration related dolomite porosity have long been recognized in the zinc districts in Tennessee.  For hydrothermal dolomite plays, drilling off structure may be better than drilling on structure. Locating this structure in Swan Creek was as a result of secondary target development, with the Knox Group the original primary target. Oil shows are widespread in Swan Creek in the Stones River and Nashville Groups, but most oil production here is from these dolomites. Wells associated with this hydrothermal event and proximity to their off-structure locations, and disproportionate high cumulative volumes, warrant special economic considerations and investigation.