Dictionary:Well log

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A record of one or more physical measurements as a function of depth in a borehole. Also called a borehole log. Distinction is sometimes made between a log as an entire record (which may contain curves showing several measurements) and the individual curves themselves, which are also called logs. 1. Wireline logs are recorded by means of sondes carrying sensors which are lowered into the hole by a cable. Examples include logs which record electrical measurements (SP, resistivity, etc.), acoustic measurements (sonic, 3D, etc.), nuclear measurements (natural radioactivity, neutron logs, etc.), and miscellaneous measurements (hole size, temperature, etc.). 2. Other types of well logs are made of data collected at the surface; examples are core logs, mud logs (q.v.), drilling-time logs, etc. 3. Measurement-while-drilling (q.v.) logs. 4. Still other logs show quantities calculated from other measurements; examples are moveable-oil plots, synergetic logs, etc. Pickett (1970) lists types and applications of well-log measurements, as shown in Figure W-9.