An Independent Comparison Of Borehole Imaging Tools And Their Geological Interpretability

This paper addresses questions increasingly posed by formation evaluation professionals. Will an azimuthal density tool see fractures? Can we get detailed sedimentological data with an oil based image log? Do we need to acquire core and micro-resistivity images in these wells? We are designing completions right now, will a televiewer help us? Borehole images are commonly acquired on wireline cable, pipe and logging while drilling (LWD) acquisition systems and there are now images for virtually all mud systems. The capacity of an image log to record geological bedding and formation features is substantially a function of measurement density, sample spot size and sample rate. The physics of the measurement method and resultant „band width‟ of the data acquired affects the intrinsic resolution of the image resulting in a very wide range of feature recognition capabilities for the various measurement types. Generally (but with exceptions) higher sample rate and higher resolution images are produced by wireline systems. Lower resolution and lower bandwidth measurements tend to be run on LWD. High angle and long reach wells are frequently imaged with LWD tools. The resultant borehole-to-bed geometries in these highly deviated wells can mitigate lower intrinsic-image-resolution and hence add application value to low resolution LWD tools reducing interpretation uncertainty. Before designing an image logging program, the interpretation objectives must be clearly defined and will be of key importance in tool choice, given the constraints imposed by the proposed well and budget. There is no single test well or dataset where all image measurements types have been run and compared systematically. However, we have now assimilated sufficient well datasets, where multiple image types have been acquired in the same lithological section, to provide statistical comparisons of dip density and feature recognition across all log types.