Borehole
Micro-
Imaging
Applied to Siliceous Shale Reservoir
Characterization
Scott J. Johnson and Maged Y. Fam
Electric and acoustic borehole
micro-
imaging
logs greatly aid
characterization of siliceous shale reservoirs.
Borehole
images yield reservoir
data not attainable with conventional open-hole logs. While visual inspection of
core remains indispensable,
borehole
images enhance visualization and facilitate
orientation analysis of sedimentary, structural and diagenetic features. Style,
density, and interconnectivity of natural fractures are assessed directly and
fracture aperture is estimated under in-situ stress. Inspection of the
borehole
wall and cross-sectional geometry are used to constrain maximum horizontal
in-situ stress orientation.
Borehole
micro-
imaging
logs have been applied to characterize siliceous shale
reservoirs in the Cymric Field of California. Significant variations in
reservoir permeability due to natural fracturing are evident both vertically and
laterally. Fracture-enhanced system permeability may impact depletion geometry
to the extent that fractures are not induced during cyclic stimulation.
Macroscopic reservoir heterogeneity is greatly enhanced by silica diagenesis
resulting in improved image quality. Maximum horizontal in-situ stress
orientations inferred from
borehole
images are comparable to geophysical stress
measurements. Stress barriers are evident and may limit height growth of induced
fractures. Reservoir characterization has improved well completion practices by
allowing perforations to be strategically placed with respect to potential thief
zones thereby reducing the possibility of bypassing hydrocarbons.
AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California