A Comparison Of Fracture Characterization Techniques Applied
Modern borehole measurement systems designed for fracture characterization are generally based on one of three principles: electrical conductivity of fluid-filled fractures; acoustic attenuation during propagation across fractures; and borehole wall imaging. The fracture responses from at least one prototype fracture detection system in each of these categories are compared for a limestone interval of consistent lithology. Most fractures contained in the core from the test interval are nearly vertical in orientation, and the natural width of many fractures can be measured on the intact core samples. Measured fracture apertures are no more than 1 mm(millimeter) in all but one case, approaching the probable limits of resolution of the systems being tested. The acoustic borehole televiewer (a wall imaging device) gives the most detailed information about the borehole wall, but apparent fracture widths commonly are a full order of magnitude greater than measured core fracture widths. All other devices tested (microresistivity dipmeter, acoustic waveform amplitude recording system, and two versions of the circumferential acoustic probe) show recognizable responses for one set of identified core fractures, but many additional fractures are apparently beyond their limits of resolution.
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