--> Abstract: Identification and Characterization of Pressure Seals through the Use of Wireline Logs: A Multivariate Statistical Approach, by G. R. Moline, P. A. Drzewiecki, and J. M. Bahr; #91004 (1991)

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Identification and Characterization of Pressure Seals through the Use of Wireline Logs: A Multivariate Statistical Approach

MOLINE, GERILYNN R., PETER A. DRZEWIECKI, and JEAN M. BAHR, University of Wisconsin--Madison, Madison, WI

A study is currently underway to investigate the occurrence of pressure compartmentation in the St. Peter Sandstone of the Michigan basin. In particular, we are interested in identifying and characterizing the seals that bound these compartments. Commonly, the existence of a pressure seal is inferred through the identification of vertical discontinuities in the pressure gradient. Often, though, the pressure data are neither dense enough nor extensive enough to specifically locate these seals. An alternative, in cases where only sparse pressure data are available is to locate zones with sufficiently low permeabilities to allow preservation of pressure differentials over geologic time scales. Direct measurements of permeability from in situ well tests and core plug evaluations are not r adily available for the St. Peter, however, because this formation is an active gas play and most data are proprietary. Wireline logs provide an alternative means for estimating permeability. More than 500 wells have been drilled to the St. Peter, and the wireline logs for these wells provide an extensive data set. In this paper a multivariate statistical approach is used to discretize the wireline logs into "electrofacies" and to correlate these electrofacies with lithofacies descriptions and hydraulic parameters from core analyses. On the basis of these correlations, the electrofacies associated with very low permeabilities, i.e. potential seals, are characterized. These electrofacies characterizations are then used to identify "tight" zones in individual wells and to correlate between wells, providing a picture of the vertical and lateral distribution of potential seal zones throughout the basin.

(This research was supported by a grant from the Gas Research Institute.)

 

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)