Wireline logging is the practice of continuously collecting and recording data from a borehole during the drilling process. This usually occurs in the context of oil and gas exploration, where wireline logging generates valuable information for making decisions about how and where to drill, and when to stop drilling. Logs become part of the permanent data record associated with a well, with the company storing them in case they are needed for future reference. Usually, a wellsite geologist supervises wireline logging.
To collect a wireline log, sensor tools on long cables are inserted into the well. People can choose to log data while lowering or raising the sensors, depending on the situation. Wireline logging provides continuous feedback, measuring properties like electrical conductivity, density, and so forth. These differ from measurements of samples taken on the surface, like the mud samples from the drill a geologist will analyze to collect more information about the geological formation.
People can use wireline logging to generate a profile of the formation they are drilling, and this data can be part of the process of deciding when to stop drilling. Wireline logs from neighboring wells are available for comparison to learn more about what to expect in the well. Hitting a deposit of oil or gas may be a good sign, but it could be a small pocket, rather than a deep and productive deposit. The geologist needs to be able to make practical decisions about drilling to increase productivity.
A geologist can turn to a number of tools in wireline logging. The equipment may send real time data along cables to the surface, or store data and print it out later, depending on the setup and the needs of the situation. The equipment is often expensive, and care is taken to maintain the wireline logging system to keep it functional. Geologists may be familiar with the basic principles of maintaining and calibrating equipment in the field so they do not have to send it out whenever a problem arises.
In addition to being useful for oil and gas companies, wireline logs can also be helpful for geologists in general. Oil and gas exploration provide a wealth of data about geology and the composition of the earth's crust in various regions of the world. While companies often want to keep data confidential for security reasons, some material may be accessible to researchers in special circumstances.