Evaluating the Effects of Lithofacies and Thin Shales on the Lateral Distribution of Hydrothermal Dolomite Reserviors in the Michigan Basin
The southern Michigan Basin contains numerous hydrothermal dolomite hydrocarbon fields, including the giant Albion-Scipio Field. The fields typically encompass narrow zones of faulting and fracturing which have been altered from a tight host limestone into a more porous and permeable dolomite by upward-moving hydrothermal fluids. Alternating layers of dolomite that spread laterally away from the main vertical fault conduits imply that structure alone may not define the resulting reservoir architectures within the region. A detailed analysis of primary depositional facies and thin shale seams suggests that secondary stratigraphic controls play a significant role in the development of reservoir rock within these Ordovicianaged Trenton and Black River fields. This study incorporates core analysis, wireline logs, petrography and X-ray diffraction to investigate preferential migration of hydrothermal dolomite away from vertical faults. The results of this project will help eliminate the risk of drilling close, stepout dry holes along the elongate trends and may lead drillers to more accurately pinpoint the hydrocarbon-producing zones.