Chapter%205 - Petrophysics MSc Course Notes 5. WIRELINE...

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Petrophysics MSc Course Notes Wireline Logging Dr. Paul Glover Page 55 5. WIRELINE LOGGING 5.1 What is a Wireline Log A log is a continuous recording of a geophysical parameter along a borehole. Wireline logging is a conventional form of logging that employs a measurement tool suspended on a cable or wire that suspends the tool and carries the data back to the surface. These logs are taken between drilling episodes and at the end of drilling. Recent developments also allow some measurements to be made during drilling. The tools required to make these measurements are attached to the drill string behind the bit, and do not use a wire relying instead on low band-width radio communication of data through the conductive drilling mud. Such data is called MWD ( measurement while drilling ) for simple drilling data, and LWD ( logging while drilling ) for measurements analogous to conventional wireline measurements. MWD and LWD will not be covered by this course, although the logs that are produced in this way have very similar characteristics, even though they have been obtained in a completely different way. Figure 5.1 shows a typical wireline log. In this case it is a log that represents the natural gamma radioactivity of a formation. Note that depth is arranged vertically in feet or metres, and the header contains the name of the log curve and the range. This example shows a single track of data. Note also that no data symbols are shown on the curve. Symbols are retained to represent discrete core data by convention, while continuous measurements, such as logs, are represented by smooth curves. Figure 5.1 shows only 50 m of borehole, but real logs are often much longer (thousands of metres), and contain multiple curves on a single track such as this, and multiple tracks. Fig. 5.1 Example of a Gamma Ray Log GAMMA RAY (GR) 100 0 630 620 API UNITS 640 670 660 650
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Petrophysics MSc Course Notes Wireline Logging Dr. Paul Glover Page 56 Figure 5.2 A typical log set
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Petrophysics MSc Course Notes Wireline Logging Dr. Paul Glover Page 57 An example of a more usual log is given as Fig. 5.2. This log contains 3 tracks and many different sets of log data. There is a very large range of basic logs that can be run in a well, and an even greater number of derived logs, i.e., data that can be plotted in log form that is calculated from the basic logs. Examples of the basic physical parameters that can be measured down-hole with logs include (a) the size of the borehole, (b) the orientation of the borehole, (c) temperature, (d) pressure, (e) the natural radioactivity of the rocks, (f) the acoustic properties of the rocks, (g) the attenuation offered by the rocks to radioactivity generated from the tool, (h) the electrical properties of the rocks, (i) the NMR characteristics of the rocks, and so on. Examples of derived logs include (a) porosity derived from the sonic or density log, (b) water
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Chapter%205 - Petrophysics MSc Course Notes 5. WIRELINE...

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