Gathering the right geophysical data for your needs requires precision and accuracy. Probing and logging information with boreholes gives you access to different data from groundwater investigation to exploration for minerals.
Different core logging techniques are used for collecting variations of data, including porosity, mapping, exploration, and more. Knowing these different techniques helps you choose the right tools to bring on location. Before starting your project, become familiar with the following techniques.
Video
Using a camera to inspect your well lets you clearly see its condition all the way down to the bottom. A camera will tell you the conditions of the well bore and its casings, current and historic water levels, the presence of bacteria in the well, and a variety of other data. Using a borehole camera and monitoring your findings on video gives you a better idea of your baseline data for accurate findings.
Video logging is beneficial at all stages of borehole logging. If a borehole is older, you can use the video to see if there are areas in which it has deteriorated. If you are drilling a new borehole, you can use the camera to orient your equipment and inspect the initial hole before reinforcing it.
Portable loggers
Collecting and logging data can be automated with a variety of portable loggers. Portable probes are lightweight and easy to read, offering different data points that you can program into the logger. There are different models that you can use to collect data from shallow areas and areas of greater depth. Most are operated with software that can be synced with a PC.
In order to collect accurate data, the logging cables are coated in plastic. You can easily clean them between measurements, resulting in better data. There is no need to worry about an inaccurate measurement because the probe cable was contaminated with sediment from a different site. When you need to quickly collect data with multiple parameters, this tool can do so with accuracy.
Resistivity
To determine the characteristics of rocks or sediments within a borehole, you can use the resistivity method. Different methods for measuring resistivity include electromagnetic induction logs, fluid resistivity, temperature, and others. A common method of resistivity logging involves using electrodes to measure the resistance of materials within the formation.
Resistivity is also used to check formations for porosity and fluid saturation. Normal resistivity is typically conducted in shallow areas by spacing electrodes in a varying pattern on the probe. The frequency of the electrical current is impacted by bed thickness, porosity and other features within the formation. For deeper areas, you can log resistivity using an induction technique. This involves the use of an induction transmitter coil that is used to create a magnetic field that impacts the flow of the electrical current. It helps produce more accurate readings in deeper areas.
Gamma Ray Logging
Another method of logging with a wide range of uses is gamma ray logging. This technique involves measuring gamma radiation that naturally occurs in formations to determine the character of the rock or formation. All rocks emit gamma radiation, but they release it in different frequencies. By measuring the gamma rays, you can determine the shale content of the area around the borehole.
Gamma ray logging is a slower method of data collection. You need to take measurements for several minutes, because of the frequency at which gamma rays are emitted. It can be used for a variety of data, including determining bedrock boundaries and estimating the thickness of an aquifer. You can also use this tool to determine uranium concentrations in the formation.
Porosity Logs
This technique is used to create an estimate of a rock’s porosity. Porosity can be measured with tools that evaluate density and by measuring the acoustic velocity. Density is estimated with gamma ray tools, while acoustic velocity is measured using sonic waves. By scattering ultrasonic waves on the surface of a formation, you can measure the rate at which they bounce off of different types of rocks. Sound waves move differently depending on the density of the material.
Using ultrasonic waves to estimate porosity is a reliable and tested technique. It can be used to measure borehole fluids and casings and to evaluate the permeability of a formation.
Nuclear Magnetic Resonance
Another method of determining porosity is though the use of nuclear magnetic resonance (NMR). This method is conducted by measuring signals from a magnetic response within the formation. NMR also gives you the ability to measure water content by volume and hydraulic conductivity, among other measurements.
NMR tools are relatively new, having gained popularity in the past decade. They offer high resolution measurements and accurate data collection. You can use these tools to map an aquifer or to log how water is distributed within the aquifer. There are a variety of durable and portable tools that can be used to take these measurements.
Corrosion Well Logging
If you are working with boreholes or wells that have been operating for a long time, corrosion well logging can help you determine the integrity of existing casings. You can use tools including calipers or some of the measuring tools listed above to measure the thickness of casings and check them for areas in which they are wearing out.
Caliper tools are limited. You can supplement the use of these tools with a camera or by taking ultrasonic measurements in order to get multiple data points for analysis. Using a variety of tools is likely to result in more accurate data than you would get with one tool alone.
Borehole logging is used in a variety of industries from geotechnical services to oil and gas. With all of the tools and techniques available to collect and log data, your subsurface measurements can be analyzed with more accuracy. These tools can be integrated with software that lets you log data onsite and interpret it with ease. Being familiar with different borehole logging techniques will help you determine which method to use for all of your projects.
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