Using Core Data to Develop and Calibrate Petrophysical Models in Tight Gas Sands
Merkel, Dick
EnCana Oil & Gas (USA) Inc, Denver, CO
Rocky Mountain tight gas sand reservoirs typically have
complex mineralogy in the reservoir rock in the form of sandstone,
mica, feldspars, and carbonates. Moreover shale is often some
combination of the clays illite, smectite, kaolinite, and chlorite. The
measured signal from most logging tools originates from the rock
matrix, which in the case of these tight gas sands is often both
complex and poorly defined.
Selective coring and core analysis can be used to understand
various tool log responses in order to develop and calibrate
petrophysical models. However this requires rigorous planning that
ranges from 1) specifying core bit and mud type, to 2) shipping,
plugging and preserving core, to 3) specifying what conventional and
special core analysis is to be performed. This protocol is particularly
important in tight gas sand core analysis because some analysis needs
to be done at native state conditions while conventional core analysis
can be done at restored state (after the core is cleaned and dried).
With a selected logging suite and proper core analysis,
evaluation of complex tight gas sandstone reservoirs can be
accomplished. Examples will be shown how core analysis techniques
ranging from tritiated mud, analysis at multiple net confining stresses,
NMR, capillary pressure, mercury injection, XRD, and SEM can be
used in the generation of an integrated petrophysical model.
AAPG Search and Discovery Article #90071 © 2007 AAPG Rocky Mountain Meeting, Snowbird, Utah