The Earth’s surfaces are goldmines for oil and gas reservoirs. Since engineers and geologists cannot examine deeper into rock formations, they use special tools instead.
Specialists lower these tools into the wellbore, hoping to obtain measurements of subsurface properties. Gathered data are usually displayed as a series of measurements, which cover a depth display range known as the well log.
Well logging for geophysical purposes remains a stable option when it comes to knowing more about the Earth’s riches. But what are the secrets underneath?
The Humble Beginnings
The year 1972 saw the obtainment of the first well log in Pechelbronn field in Alsace, France. The tool, invented by Marcel and Conrad Schlumberger, measured the earth’s electrical resistance. Present engineers recorded data points retrieved from the sonde, suspended from a cable located near the borehole.
Today’s geologists also depend on sets of well logs to map out present subsurface formations. By comparing gathered logs from the field’s wells, both engineers and geologists can develop efficient and effective hydrocarbon plans.
Different Types of Logs
Once a well is drilled, formations are exposed to the well-bore. This offers an opportunity to determine the rock formation’s properties with the help of openhole logging tools. In some cases, especially with complex trajectories, companies use logging tools as part of the initial drilling assembly — an approach also known as logging while drilling (LWD).
Drillers stabilize formations using cemented metal casings in the well. The metal of the casings interfere with the logging measurements, but recently, the industry has dramatically improved its capabilities without compromising data. Metal casings can now measure formation properties and locate bypassed oil.
Measurements by Multitudes
Today’s engineers and geoscientists have access to a variety of logging tools, which offer more than just basic information. For example, imaging logs offer a 360-degree and high-resolution view of formation properties through the wall. Others bring fluid samples to the surface or measure properties as the water flows from the well.
Well-logging continues to require robust technology to better understand reservoir properties and harsh well conditions. These resources — and the people who use it — are important in fulfilling growing energy needs.