Well logging reports the depths, subsurface formations, and events that take place during drilling. Well logs can be made by lowering instruments into the well or through visual observations. These days, well logging is about anything recorded about the drilling process instead of the depth of the well. To measure the electrical, radioactive, electromagnetic, and acoustic formations, logging tools are inserted into the well. In some cases, these tools are incorporated into the drilling tool or lowered into the well at regular intervals for data collection.
Well logs are used by drillers and engineers for measuring depths of formation tops, formation thickness, water saturation, porosity, kinds of formation encountered, oil and gas presence, and other elements. The measurement data will determine the commercial viability of the well and the potential of running processes such as casing, cementing, and completion. Apart from recording what is going on below the surface, well logging predicts success. It commonly works with a FrackLock completions system to ensure more success of the drilling project.
How to Read a Well Log
A well log is composed of a header that offers specific details regarding the well. These details include the well information, operating company, the kind of log run, the graph, and the main log section. The graph works by charting the depth reached vertically. Throughout the graph at every log section, there are inserts that identify every curve. The log curves can be also called measurements, readings, or traces. They can be represented by solid, long- and short-dashed lines for deciphering the various measurements that the log represents. The log’s final part is the tool calibrations for before and after the log was made to ensure accuracy.
Kinds of Well Logs
With the improvement in well logging technology, many kinds of well logs have been introduced. Also, there are various tools used for determining different subsurface characteristics. Below are the different kinds of well logs:
- Resistivity logs. This well log measures the way electricity travels through rocks and sediments. It determines the kind of fluids present as oil and fresh water are poor conductors of electricity while formation waters easily conduct electricity and are salty.
- Spontaneous potential (SP) logs. This log calculates the electrical currents generated between the drilling fluids and formation water that the pore spaces hold. As a result, it can determine whether or not the rocks in the well are permeable.
- Induction logs. These logs are used in wells which don’t use water or mud. It makes use of the interaction of electricity and magnetism for determining resistivity.