Borehole Geophysics

Borehole Geophysics

Borehole surveys allow us to deploy geophysical instruments at depth, the benefit of which is higher resolution data that would not be achievable from the surface. At SEP Geophysical we can provide a wide range of in-situ geophysical borehole testing methods such as;

  • cross-hole and downhole seismic testing,
  • parallel seismic testing and,
  • downhole magnetometry.

Borehole surveys are often used in conjunction with other surface geophysical techniques such as seismic and electrical resistivity tomography surveys. Our team have carried out many borehole geophysical surveys across the world, providing clients with high-quality data to support their projects.

If you would like to find out more about our borehole geophysical services or discuss your project requirements, please contact us.

Parallel Seismic Testing (PST)

As the industry looks to re-use or develop existing structures, information is often required regarding the installed depth of a buried pile or sheet pile wall.

To determine pile depth a hydrophone array is lowered into a borehole placed close to the pile under investigation. The top of the pile is struck with a hammer and the propagation of seismic waves through the structure are then measured.

The point where there is a change in seismic velocity, where the seismic energy has passed from the pile into the underlying ground, indicates the depth at which the pile ends.

Downhole magnetometry

Downhole magnetometry is another effective technique for pile determination or any structure that contains steel reinforcement.

Measuring variations in the magnetic field at incremental depths down boreholes in close proximity to the structure under investigation. It is possible to identify the ‘toe’ or bottom edge of a steel or steel-reinforced structure.

SEP Geophysical would always recommend downhole magnetometry be deployed in conjunction with Parallel Seismic Testing as a complementary technique allowing for a more robust analysis of pile /structure depth.

Cross-Hole and Downhole Testing

Cross-hole testing is conducted utilising parallel source and receiver boreholes in relatively close proximity.

SEP Geophysical can conduct to a high standard, compressional and shear (P & S Wave respectively) cross-hole testing, in accordance with ASTM D4428/D4428M-14, which provides high resolution one-way seismic data for such applications as to determine engineering properties. These quantities are vital for the design process for infrastructure projects.

Applications of Cross-Hole and Downhole Testing

  • Determination of Rock Velocities
  • Calculation of dynamic elastic moduli e.g. Young’s Modulus
  • Buried Pile Depth
  • Hydrological Mapping
  • Void/Fracture Location

Similarly SEP Geophysical can also conduct downhole seismic testing in accordance with ASTM D7400/D7400M-19. This methodology differs from the cross-hole testing whereby only one borehole is required and the source(s) are positioned at the surface.

Analysis of the first arrivals at various increments down the borehole can be used to calculate the P and S wave velocities as a function of depth.

Borehole Geophysical Survey FAQs

What is a Borehole Geophysical Survey?

Borehole geophysics is the technique of deploying geophysical equipment downhole to collect high-resolution data. This data can be used to assess a wide range of geotechnical and engineering properties.

What are the benefits of a Borehole Geophysical Survey?

The main benefit of borehole geophysics is the ability to collect high-resolution data at depth. This level of detail would not be achievable from the surface, and for cross-hole testing, this would not be possible at all without drilling multiple boreholes.

What methods can be used in a Borehole Geophysical Survey?

There are a wide range of in-situ geophysical borehole testing methods that can be used, such as cross-hole and downhole seismic testing, parallel seismic testing and downhole magnetometry.

How is the data collected in a Borehole Geophysical Survey?

Data is collected by deploying geophysical equipment downhole on-site, often using a wireline system. The equipment is then used to collect data at various depths, which is then processed and interpreted to determine the desired information.

How long does a borehole survey take?

This will depend on the type of survey being conducted and the depth of the borehole. However, most surveys can be completed within a few days.

How much does a Borehole Geophysical Survey cost?

The cost of a borehole geophysical survey will depend on a number of factors, such as the type of survey being conducted, the size of the survey and the location. Contact our team for a detailed quote for your project.

How is the data interpreted?

The data collected during a borehole geophysical survey is interpreted by our team of experienced geophysicists using industry-standard software, which will vary depending on the type of data acquired on-site.

Get in Touch

Our team offers a range of borehole survey services and would be happy to discuss your specific requirements and get you the information you need. Downhole magnetometry, cross-hole and downhole testing are just some of the ways we can help your project.

Contact our team today to find out more.