The next class of well logs to be considered is generally referred to as porosity logs. Although each produces a porosity value from basic measurements, none actually measures porosity directly. Two such logs, the density and neutron, are nuclear measurements. A third log, the sonic, uses acoustic measurements, and the fourth and newest log senses the magnetic resonance of formation nuclei. When used individually, each of the first three has a response to lithology which must be accounted for, but when used in concert, two or three at a time, lithology can be estimated and a more accurate porosity derived.
Nuclear magnetic resonance (NMR) logging was first introduced by Schlumberger in 1978 (Maute, 1992) but was not initially widely used because of operational limitations. With the commercial introduction of the Magnetic Resonance Imaging Log (MRIL) by NUMAR Corporation (now part of Halliburton) in 1980 (Halliburton, 1999) and the release of the Combinable Magnetic Resonance Tool (CMR) by Schlumberger, the technique is steadily gaining acceptance.
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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.