Print this pageBasement Control of Reservoir Development of Middle Lower Ordovician Strata, Eastern North America
TEDESCO, Steven A.
Basement wrench faulting, reactivated during Upper Ordovician times, locally brecciated Ordovician carbonates along the Cincinnati-Findlay-Algonquin arch system in the Eastern North America The arch system forms the boundary between the Michigan, Illinois and Appalachian basins and is underlain by a series of Precambrian rifts. Reactivated Precambrian zones of weakness created migration pathways in th Cambrian and Ordovician strata for petroleum and low temperature hydrothermal fluids to enter these breccia zones. The wrench or strike-slip faulting along the arch system area tends to strike north to northwest-southeast. Maximum brecciation occurs in are where main wrench corridors are transected by sympathetic northeast-southwest or east-west secondary shear systems. The junction areas are characterized by "flower structures" that usually are the site of the greatest brecciation. Reservoirs tend to highly compartmentalized by en-echelon dilation fault-fractures and are discontinuous along the main wrench corridor. Dry holes are common along trend because individual compartments are separated by non-brecciated country rock During Permian Pennsylvanian times, low temperature brines were expelled from the Illinois, Michigan and Appalachian basins into the arch area. These brines dolomitized, enhanced porosity caused structural collapse and deposition of base metals in the breccia Concurrent with or later than dolomitization, petroleum migrated into many of the breccias. Major fault systems, whether normal or wrench, that were reactivated post-Ordovician, to date, have shown no indications of dolomitization, petroleum accumulation and mineralization. The use of existing models, landsat, magnetics, surface geochemistry in an integrated approach can identify the wrench corridors, junctions of secondary shears and location of petroleum productive brecchias. Examples will be presented utilizing this approach.