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The AAPG/Datapages Combined Publications Database

AAPG Special Volumes

Abstract


 
Chapter from: M 61: Basin Compartments and Seals 
Edited by 
Peter J. Ortoleva

Authors:
Jean M. Bahr, Gerilynn R. Moline, and Gregory C. Nadon

Methodology and Concepts

Published 1994 as part of Memoir 61
Copyright © 1994 The American Association of Petroleum Geologists.   All Rights Reserved.
 
Chapter 11

*
Anomalous Pressures in the
Deep Michigan Basin

Jean M. Bahr
Gerilynn R. Moline
Gregory C. Nadon
University of Wisconsin--Madison
Madison, Wisconsin, U.S.A.


*

ABSTRACT


In this chapter we examine pressures in the St. Peter Sandstone and associated formations of the deep Michigan basin. A comparison of computed brine heads to surface elevations reveals a large area of overpressures within the St. Peter Sandstone and the Glenwood Formation to the west and north of Saginaw Bay. Contrary to the patterns expected for a steady-state, topographically driven flow system, heads in these formations are highest in the regional discharge area. Vertical gradients between the Glenwood and the St. Peter and between the St. Peter and the Prairie du Chien Group would generate downward flow in the regional discharge area, which is also inconsistent with a steady-state flow system. Low-permeability zones must exist within the Glenwood and St. Peter to inhibit equilibration with normal pressures in the underlying and overlying units. Overpressures appear to be dissipating by both upward and downward leakage through high-permeability zones located in anticlinal structures and possibly related to basement faults. Within the larger area of anomalous pressures, repeat formation test data from selected wells reveal even greater overpressures locally within the St. Peter. These vertical variations in pressures are associated with vertical variations in permeability, suggesting a stacked system of compartments separated by low-permeability zones of diagenetic origin.

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