Borehole Geophysics

Borehole surveys allow us to deploy geophysical instruments at depth, taking measurements that yield higher-resolution geophysical data not achievable from the surface. At SEP Geophysical, we provide a wide range of in-situ geophysical borehole testing methods such as:

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

Borehole surveys are often combined with other surface geophysics techniques such as seismic and electrical resistivity tomography surveys. Our team has conducted numerous borehole geophysical surveys worldwide, providing clients with high-quality data to support their projects and enhance their understanding of subsurface conditions.

If you would like to learn 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 is then measured. This method can also be used to understand surrounding rocks and their physical properties.

The point where there is a change in seismic velocity, indicating the seismic energy has passed from the pile into the underlying ground, shows the depth at which the pile ends. This information can be graphically displayed for better interpretation.

Downhole magnetometry

Downhole magnetometry is another effective technique for pile determination or any structure containing steel reinforcement. By measuring variations in the magnetic field at incremental depths down boreholes in close proximity to the structure, it is possible to identify the 'toe' or bottom edge of a steel or steel-reinforced structure.

SEP Geophysical recommends deploying downhole magnetometry alongside Parallel Seismic Testing for a more robust analysis of pile/structure depth. This synergistic nature of site investigation methods provides a better understanding of subsurface conditions.

Cross-Hole and Downhole Testing

Cross-hole testing is conducted using parallel source and receiver boreholes in relatively close proximity. SEP Geophysical conducts compressional and shear (P & S Wave) cross-hole testing to a high standard in accordance with ASTM standards (ASTM D4428/D4428M-14). This provides high-resolution one-way seismic data for applications like determining engineering properties, essential for infrastructure project designs.

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 conducts downhole seismic testing in accordance with ASTM D7400/D7400M-19. This method requires only one borehole, with source(s) positioned at the surface.

Analysis of the first arrivals at various increments down the borehole can be used to calculate P and S wave velocities as a function of depth, aiding in the understanding of subsurface conditions, such as lithology, porosity, permeability, and bed thickness.

Borehole geophysics also supports well construction, groundwater monitoring and environmental studies. Techniques such as normal resistivity and electromagnetic methods help assess fluid content, soil and formation physical properties, and the surrounding rocks.

Borehole geophysical logging records geophysical logs such as temperature, resistivity and permeability at depth, providing a comprehensive picture of subsurface conditions for applications including groundwater assessment and aquifer characterisation.

Conclusion

By integrating borehole seismic surveys with surface geophysics, we provide a comprehensive understanding of subsurface conditions.

Our methods, including cross-hole and downhole testing, magnetometry, and seismic testing, yield detailed insights into subsurface formations. Contact us to leverage our expertise for your geophysical needs.

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.

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