Wireline Logging - Introduction to Wirelline Logging and Petrophysics - Part 1
Borehole Image Tool
Introduction to Wireline Logging
Wireline Logging or well logging is the process of introducing measurement sensors into a borehole/wellbore via a "wireline", an electromechanical cable with conductor wire embedded within steel armour. The objective is to measure and record the physical properties of the rocks in oil and gas wells. Electrical power and control is provided to the sensors inside the borehole from a surface logging unit. The sensors transmits to the surface, unit data representative of the physical parameters of the rock surrounding the borehole. The surface wireline logging unit consists of computers and software to control and record data, power supplies to provide power to the downhole sensors, a spool /cable drum of wireline cable, and a hoisting unit (hydraulic or electrical).
The sensors are attached to the wireline logging cable and lowered inside the borehole to the 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.
The "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.
Wireline Tool Types
Wireline tool typesTypically the wireline tools are cylindrical in shape, usually from 1.5 to 5 inches in diameter. There are three types of wireline tools:1. Tools with sensors but without excitationThere are downhole logging tools to measure spontaneous potential (SP), which is a voltage difference between a surface electrode and another electrode located in the downhole instrument. Other logging tools measure the natural radiation from natural isotopes of potassium, thorium, and uranium. Another set of tools measure pressure and temperature and fluid density.2. Tools with sources of excitation and sensorsThese sensor systems consist of a source of excitation and a sensor. In this type we find acoustic (also called sonic), laterolog, inductive, nuclear and magnetic resonance sensing systems, just to name a few.3. Tools that produce some mechanical work or retrieve a sample of fluid or rock to the surface.These are devices to collect samples of rock, samples of fluid extracted from the rock. Other tools are mechanical devices.