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