Well-log tomography and 3-D imaging of core and log-curve amplitudes in a Niagaran reef, Belle River Mills field, St. Clair County, Michigan, United States

Well-log tomography, a recently developed technique that generates subhorizontal slices through log curves, was used to create a series of amplitude slices from the core permeability, core porosity, and gamma-ray log curves for the wells penetrating the Silurian Brown Niagara reservoir in the Belle River Mills field. Log-curve amplitude slicing and three-dimensional (3-D) imaging of the core permeability and core porosity amplitudes show the detailed anatomy of the pinnacle reef in terms of these important reservoir properties. Although the reef has been dolomitized, the spatial distribution of permeability and porosity amplitudes in the reservoir appears to be controlled by the original pore and depositional fabrics of the wackestone, boundstone, stromatolite, and reef conglomerate rock types. Trends and patterns observed in the normalized gamma-ray log tomography approximate the trends and patterns observed in the core permeability and core porosity tomography in the Belle River Mills field. The similarities in the tomography trends and patterns establishes a potentially significant relationship that can be used to interpret log-curve amplitude patterns in other Niagaran pinnacle reef fields with log-curve data only and perhaps lead to improved sequence-stratigraphic models for these reservoirs. Well-log tomography and 3-D imaging provide complementary visualization tools that use existing data to image reservoirs and geologic formations. These imaging tools can be used to improve the design and placement of vertical, deviated, and horizontal wellbores for primary, secondary, tertiary, and gas storage operations in these reefs and other reservoirs.