Laird B. Thompson¹, Donald A. Best², James P. Wallace¹, Peter H. Hennings³

(1) Independent, Dallas, TX
(2) ExxonMobil, Houston, TX
(3) Phillips Petroleum Company, Bartlesville, OK

ABSTRACT: Borehole Image Logs -- Rosetta Stones or Red Herrings in Quantifying Fractured Reservoir Productivity?

Electric, acoustic and visual borehole image logs show features of the borehole wall in great detail. They may "see" features only millimeters in size, and are sensitive to a wide variety of geological elements. Their detailed representation of faults and fractures has led to an industry renaissance in the study of "fractured reservoirs". Fracture frequency logs and rose diagram plots of fracture orientations are now common products in image log interpretation. But are these really useful in understanding and predicting those damage elements that are controlling flow in these reservoirs?

The borehole wall is the dynamic focal point of stresses encountered and created by the drilling process. The wall often preserves such features as natural fractures, drilling induced fractures (tensile, shear and compressional), tool marks, and other geological and artificial features. Recognizing and cataloging these features is not always a simple task. Once natural faults and fractures are identified and documented, their genetic relationships and 3-D distribution can be examined. Unfortunately, this is a daunting task if 1-D wellbore scan line data are all that are available. Finally, quantitative values for fracture porosity and permeability are needed. Image logs inherently cannot provide these data.

This study proposes a methodology for integrating image data with other petrophysical analyses and with other production data to obtain quantitative porosity and permeability values for faults and fractures intersected by the wellbore. Further, by placing these values on a 3-D structural model of appropriate geological surfaces, these values can be predictively distributed throughout the reservoir for calculating STOOIP and optimizing production.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado