Identification
and Characterization of Subsurface Cave Systems Using Micro-Resistivity
Image Wireline Logs
Larsen, L. Mark1, Robert
Loucks2 (1) Schlumberger, Addison, TX (2) The
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