Wireline Logging
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Wireline Logging consists of measuring and recording the physical properties of the rocks in oil wells. "Logging" consists of introducing sensors in a borehole via a "wireline", an electromechanical cable. Power and control is provided to the sensors inside the borehole, from a surface unit. The sensors send to the surface unit data representative of the physical parammeters of the rock sorrounding the borehole. The surface unit consists of computers to control and record data, power supplies to provide power to the downhole sensors, a spool of wireline cable, and a hoisting unit.
The sensors are lowered inside the borehole, to its bottom. Then, they are pulled up by spooling the cable using the hoist unit. As the sensors are moved up at a more or less constant speed, the sensors measure the properties of the rock, and send the data to the surface unit for recording, control and display.
A "wireline", in this context, is the name of the electromechanical cable that is used to provide power and control to the downhole sensors, and to send data to the surface. It also serves as the stress member that supports the weight of the "logging tools" or "logging instruments" that contain the sensors.
Typically the wireline tools are cilyndrical in shape, usually from 1.5 to 5 inches in diameter. There are three types of wireline tools:
- Those with sensors without excitation
- Tthere are units to measure spontaneous potential (SP), which is a voltage difference between a surface electrode and another electrode located in the downhole instrument, other instruments that measure the natural radiation from natural isotopes of Potassium, Thorium, etc., to measure pressure and temperature, etc.
- Those with sources of excitation and sensors and
- There are sensor systems consistent of a source of excitation and a sensor. In this type we find acoustic (also called sonic), electric, inductive, magnetic resonance, sensing systems, just to name a few.
- Those instruments that produce some mechanical work, or retrieve a samnple of fluid or rock to the surface.
- Devices to collect samples of rock, samples of fluid extracted from the rock, and some other mechanical devices.
