Dolomite Distribution, Structure, and Geometry of the Napoleon Trenton-Black River Field, Jackson County, Michigan

John H. Fowler
Polaris Energy, Inc. Jackson, Michigan, [email protected]

The Trenton and Black River Limestone formations, when altered by hydrothermal processes to porous and permeable dolomite, have been important oil producers since the earliest days of the petroleum industry in North America. In 2006 and 2007, the success of 3D seismic in extending Michigan’s giant 50-year old Albion-Scipio Field in both northerly and southerly directions, led West Bay Exploration Company and partners to consider 2D seismic reconnaissance to explore for new oil fields away from the established Albion-Scipio Trend. Seismic reconnaissance focused on Jackson County, and a promising anomaly was identified there. Additional 2D and 3D seismic work confirmed the feature, and a test well encountered Trenton dolomite pay in the morning of Nov. 22, 2008. Subsequent drilling of more than 43 productive wells over a distance of 12 miles has confirmed a classic narrow, linear, northwest-trending reservoir that includes both the Trenton and Black River formations.

Lateral and vertical wells have both been used to develop the Napoleon field, whose rocks display a variety of petrophysical characteristics related to faulting and hydrothermal alteration. Within the greater oil-productive outline, at least four separate reservoir compartments are shown to be present by bottom-hole pressures and fluid contact levels. All reservoir compartments are driven primarily by gas expansion, with most wells flowing for a significant time after initial production. Compartment separation is best explained by the concentration of hydrothermal fluid flow along a basement-involved, left lateral wrench fault system with right-stepping en echelon offset. Development drilling is ongoing. The Napoleon Field shares many similarities with the Stoney Point Trenton-Black River Field, discovered 18 miles to the west in 1982, and proves that significant conventional hydrocarbon reservoirs remain to be found in mature areas that are often thought to lack opportunity for new discoveries.

AAPG Search and Discovery Article #90154©2012 AAPG Eastern Section Meeting, Cleveland, Ohio, 22-26 September 2012