An important application of borehole image data is image feature validation against core from the same wellbore. Comparison of depth-resolved core with image data provides a “ground-truth” for image features. Because coring is exceptionally expensive, image logs provide a “core-like” proxy in parts of the field without core. Cores are seldom collected across the entire drilled interval of a wellbore. Image logs, however, are readily acquired across larger intervals, yielding more comprehensive information.
In the example here, 180′ of core is compared to image log and gamma data. The lighter portions of the core, comprised of sandstone, correspond with a lower gamma response and a lighter (more resistive) color on the image log. Dark-colored rock in the core, comprised of mudstone and shale, is matched up with higher gamma responses and darker (more conductive) image colors.
The picture above is a zoom of the core and image log showing a bioturbated sandy interval between shales. This stacking pattern dominates the cored interval and makes it difficult to perform petrophysical evaluation because reduction of formation resistivity by shales make these zones look wet. Combining the resolution of the image log with NMR and dielectric data facilitates accurate SW calculation in laminated rock. This type of analysis, in a vertical well, can enhance accurate EUR calculation and can facilitate identification of horizontal target zones.