Open-hole (Wireline) logging is one of a very large range of measurements and analytic techniques used in formation evaluation of oil wells.
Wireline logging provides the great meeting place for all formation evaluation methods in oil wells. Only through open-hole logging can a continuous record of measurement versus depth be made of so many formation properties. In particular, wireline logs can record formation electrical resistivity, bulk density, natural and induced radioactivity, hydrogen content, and elastic modulae. These raw measurements can then be interpreted to give a continuous measurement -versus-depth record of formation properties such as porosity, water saturation, and rock type. Almost without exception, every well drilled for hydrocarbons (oil and gas) is logged with wireline instruments.
With the price of oil at such a high right now, more and more oil operating companies are gearing up for more drilling, and therefore more wireline logging, to maximize their profits at this time of high oil prices.
The actual running of a log involves lowering a tool at the end of a logging cable into an oil/gas well. A sensor, incorporated in a sonde together with its associated electronics, is suspended in the hole (well) by a multiconductor cable. The signals from the sensor are conditioned by the downhole electronics for transmission up the cable to the control panel at surface which in turn conditions the signal for the recorder. As the cable is raised or lowered, it activates some depth-measuring device, a sheave wheel (pulley) which in turn activates a recording device. Finally, some form of reproduction takes place to provide a hard copy of the recorded data which is called the well log.
In general, wireline logging jargon distinguishes between a logging survey/run, a logging tool, and a log as well as a curve. There is frequently some confusion about these terms when logging matters are discussed. A logging survey is provided by a logging service company for a client. During the course of the logging pass/survey, the logging engineer may employ several logging tools, and record several different logs on each of which are presented several different curves. The logging tools used, in turn may be composed of multiple sensors.