--> Abstract: Identification and Characterization of Subsurface Cave Systems Using Micro-Resistivity Image Wireline Logs; #90063 (2007)

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Identification and Characterization of Subsurface Cave Systems Using Micro-Resistivity Image Wireline Logs

 

Larsen, L. Mark1, Robert Loucks2 (1) Schlumberger, Addison, TX (2) The University of Texas at Austin, Austin, TX

 

Subsurface cave systems form economical regional groundwater aquifers and hydrocarbon reservoirs in many parts of the world. Cave-system development is a dominant karst diagenetic process at a regional scale in creating widespread three-dimensional megapore systems near the surface. During burial, these cave systems collapse forming extensive brecciated and fractured porosity zones that are characterized by high permeabilities. These systems have been primarily studied through surface access to actual caves, quarries, and outcrops. Subsurface studies are primarily based on cores, wireline logs, and seismic data.

 

This presentation illustrates the utility of using micro-resistivity devices to recognize, characterize, classify, and quantify paleocave facies using models derived from surface studies, and applying these concepts to studies of the subsurface. Micro-resistivity image logs allow the visual interpretation of geological features such as bedding, breccia, fracture, and pore types. Distinguishing disturbed versus undisturbed host rock is easy. Chaotic, mosaic, and crackle breccias can be defined. Calculation of fracture dimensions and direction can be completed over large intervals. Cave-sediment fill can be recognized when micro-resistivity image data are integrated with other wireline logs. Image logs provide additional data that can be used to develop and quantify components of the complex pore networks encountered in buried cave aquifers and reservoirs. These data and the reservoir implications can be used to guide exploration and exploitation.

 

AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California