Borehole images are electronic pictures of the rocks and fluids encountered by a wellbore. Such images are made by electrical, acoustic, or video devices which have been lowered into the well. Images are oriented, they have high vertical and lateral resolution, and they provide critical information about bedding dip, fractures, faults, unconformities, paleocurrent directions, vuggy and fracture porosity, and other geological features. Case studies have shown that borehole images are best used in conjunction with other available wellbore data, such as other logs, cuttings, cores, and production data.
Because of the high expense and risk, relatively few wells are now being cored. Cores taken are generally short, so they may miss all or part of the target formation. In exploration wells, the depth to the target formation may even be unknown. Some lithologies tend to have poor core recovery, such as unconsolidated sands, and fractured, vuggy, or brecciated intervals. In some cores, the electrical or acoustic contrast between different lithologies may be more significant than the contrast apparent to the human eye. In recent years, all of these factors have led to the increased use of borehole images to characterize subsurface sedimentary rocks. This chapter provides a guide to the acquisition, processing, and interpretation of borehole images.
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Basic well log analysis
This publication is a general introduction to common openhole logging measurements, both wire line and MWD/LWD, and the interpretation of those measurements to determine the traditional analytical goals of porosity, fluid saturation, and lithology/mineralogy. It is arranged by the interpretation goals of the data, rather than by the underlying physics of the measurements. The appendix files contain digital versions of the data from the case studies, a summary guide to the measurements and their interpretation, and a simple spreadsheet containing some of the more common interpretation algorithms. This Second Edition of Basic Well Log Analysis delivers a great impact on training and self-training along with superior workbook exercises, newer measurements, borehole imaging, and nuclear magnetic resonance in separate chapters, all directed to provide a guide through the lengthy and sometimes ambiguous terminology of well logging and petrophysics. It provides readers with interpretation examples (and solutions) so that the techniques described here can be practiced.