Print this pageNew Insights from Interpreting Borehole Electrical Images in Carbonate Rocks
HAMMES, URSULA
Electrical imaging tools in boreholes are becoming increasingly important in interpreting the rock record. In addition to identifying fractures and faults and helping better target perforation intervals, borehole-imaging logging tools are increasingly important for mapping facies and reservoir geometries. These tools produce electrical microconductivity images of the formation sequence encountered in the wellbore, which are interpreted using an interactive graphics workstation. High-resolution (approx. 2.5 mm) and nearly complete borehole coverage can greatly increase the detail and precision of geological interpretations. Yet, to be fully useful, borehole images must be calibrated with core. This study provides the first comprehensive comparison of carbonate features with a suite of all currently available electrical image logs.
Cores of karsted and fractured carbonates of the Ordovician Ellenburger Formation, West Texas, were selected for study because many carbonate reservoirs throughout the rock record are extensively fractured, brecciated, karsted, and dolomitized. Typically, cavernous or highly fractured intervals are the most productive zones in Ellenburger reservoirs. These intervals are usually not detected in cores that commonly show no recovery or rubble within these zones. Borehole imaging provides insight into the karst stratigraphy, location of cavernous porosity, chaotic breccias or conglomerates, and highly fractured intervals.