Sequence Stratigraphy and 3-D Reservoir Characterization of a Silurian (Niagaran) Reef - Ray Reef Field, Macomb County, Michigan

Jessica L. Wold, Michael G. Grammer, and William B. Harrison
Western Michigan University Department of Geosciences; Michigan Geological Repository for Research and Education (MGRRE); Kalamazoo, MI

Silurian age (Niagaran) reefs in the Michigan Basin have long been interpreted as relatively homogeneous units, despite production histories that strongly suggest the reefs are heterogeneous in both lateral and vertical dimensions. In an attempt to better illustrate reservoir heterogeneity in these reefs, a 3-D sequence stratigraphic model was produced for the Ray Reef Field. The Petrel model incorporates twenty-eight wells in the field using a combination of gamma ray and neutron logs, porosity and permeability data from whole core analysis, and facies descriptions. Six depositional facies were determined by analyzing rock fabric, depositional attributes, and faunal changes in eight full length cores evenly distributed within the reef complex. Comparison of porosity and permeability values within the various depositional facies clearly show trends related to the individual facies. The mud dominated bioherm (deep marine) and restricted environment (shallow) intervals have low porosity and permeability values related to low initial porosities in the primary depositional fabrics, whereas higher porosity and permeability values are observed in the framework reef and grainstone facies. Incorporating the sequence stratigraphic framework into the 3-D model illustrates the episodic nature of reef growth as exhibited by the stacked nature of reef and capping grainstones, often separated by well-developed exposure horizons. Utilization of the sequence stratigraphic approach also illustrates that the vertical reservoir heterogeneity often observed in these reefs, may be controlled in large part by the combination of the vertical stacking patterns of facies, especially framework reef and capping grainstones, and with the development of significant bounding exposure horizons.

Presented AAPG Eastern Section Meeting, Pittsburgh, Pennsylvania 2008 © AAPG Eastern Section