Exploring for Hydrothermal Reservoirs in the Appalachian Basin
R. G. Hickman1, W. N. Kent2, J. R. Martin3, and M. E. Odegard3
1Structural Solutions, Sugar Land, TX
2Kent GeoScience Associates, Richmond, TX
3GETECH, Stafford, TX
Fractured hydrothermal dolomite reservoirs in the Trenton-Black River Group have produced large amounts of oil from the Bowling Green fault trend of Ohio, the Albion-Scipio and Stoney Point fields of the southern Michigan basin and numerous smaller fields in southern Ontario and Ohio. Recent high-productivity gas discoveries in similar reservoirs in New York and West Virginia have spurred exploration interest for these types of accumulations in the Appalachian basin.
All of these fields are long and narrow, reflecting the role of faults in channeling the dolomitizing fluids and focusing hydrocarbon migration. The reservoir rock consists of vuggy, brecciated, locally cavernous dolomite. Lateral and top seals are provided by the unaltered formation that consists of tight, platform limestones with minor argillaceous interbeds. Secondary minerals and fluid inclusion data indicate the dolomitizing fluids were hot, saline fluids similar to those responsible for formation of Mississippi Valley type lead-zinc deposits. Circumstantial evidence suggests that the reservoirs formed in Late Paleozoic time. Typing of oils indicates probable derivationfrom interbedded Ordovician source rocks. In the Appalachian basin, dolomitization is associated with reactivated faults related to earliest Paleozoic rifting of Laurentia or with Grenville-age structures.
In the past, deliberate exploration for this type of accumulation has not been highly successful. However, modern seismic techniques now provide keys to prospect identification. Integration of publicly available geologic maps, potential field maps, digital terrain models, well and seismic data, with a conceptual exploration model provides a cost-effective means to identify high-graded, focused exploration areas. The focus areas can be used to maximize a company’s seismic acquisition budget to acquire seismic data that can indicate prospect level evidence of fractures and dolomite reservoir development.
AAPG Search and Discovery Article #90900©2001 AAPG Eastern Section Meeting, Kalamazoo, Michigan