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Book Chapter

Example of a Logged Natural Fracture Zone

Published:
January 01, 1990

Abstract

One particular 23-ft (7-m) section of core provides excellent examples of characteristics commonly used to distinguish natural fractures from those that are drilling- or coring-induced (Figure 56 and Enclosures 1 and 2). The continuous section penetrated a fracture zone containing at least eight parallel natural fractures, each with a discrete plume. One drilling-induced fracture was observed. The overlapping natural fractures within the zone are closely spaced (1 cm or less), and most fractures show upper or lower boundaries that overlap and hook into adjacent overlying or underlying fractures within the core. The connected fractures, each the result of a single fracture event, link together to form two large composite fracture faces within the core (Figure 56). The composite pattern is similar to that developed by overlapping cooling joints (DeGraff and Aydin, 1987). Finley and Lorenz (1988) classify a similar pattern at smaller scale in sandstones of the Mesaverde Formation as vertical extension fractures. However, they describe the fracture traces as en echelon because each seg-ment did not appear to hook into its neighbor in the two-dimensional view afforded by the core surface. Cored vertical fractures probably do hook into each other in the third dimension, as indicated by outcrop studies of the Mesaverde Formation (Lorenz et al., 1989). Lorenz et al. (1989) propose a vertical connection, whereas our example here documents a horizontal link.

Such fracture connection increases the vertical conductivity of the planar fracture openings. Additional fractures that were not cored may also exist within the zone. Enclosures 1

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Contents

AAPG Methods in Exploration

Fractured Core Analysis: Interpretation, Logging, and Use of Natural and Induced Fractures in Core

B. R. Kulander
B. R. Kulander
Department of Geological Sciences Wright State University Dayton, Ohio, U.S.A.
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S. L. Dean
S. L. Dean
Department of Geology University of Toledo Toledo, Ohio, U.S.A.
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B. J. Ward, Jr.
B. J. Ward, Jr.
Amoco Production Company Research Center Tulsa, Oklahoma, U.S.A.
1
Currently with Associated Fracture Consultants, Broken Arrow, Oklahoma, U.S.A.
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American Association of Petroleum Geologists
Volume
8
ISBN electronic:
9781629811260
Publication date:
January 01, 1990

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