VEXRAD • Technical Comparison Guide
Virtual Borehole vs Conventional Geophysics.
There is no universal “best” geophysical method. Seismic, MT, EM, IP, resistivity, GPR, ADR and physical drilling measure different properties, at different scales, with different strengths and limitations. The useful question is: which combination best reduces uncertainty for this target?
First principle
Different methods see different versions of the subsurface.
Physical property
Gravity responds to density. Magnetics to magnetic susceptibility. Electrical and EM methods to electrical properties. Seismic to elastic contrasts. ADR interrogates electromagnetic/dielectric response.
Geometry & scale
A regional survey, a 2D line, a 3D volume and a point-based depth profile answer different questions. Survey geometry matters as much as method name.
Ground truth
All remote methods require interpretation. A physical borehole directly samples a narrow path through the ground and remains the definitive validation tool.
At a glance
What does each method contribute?
Where the Virtual Borehole really sits
Geophysics in acquisition. Petrophysics-like in output.
ADR is acquired remotely from the surface using electromagnetic measurements. But the Virtual Borehole is designed to organise the interpretation vertically with depth — making its product concept closer to a remote, petrophysics-style log than to a conventional plan-view anomaly map.
Map or image the physical-property contrast.
Surface / airborne acquisition
↓
Measured field response
↓
Anomaly / inversion / section / 3D model
↓
Geological interpretation
↓
Drill target
Interrogate a selected location with depth.
Surface ADR acquisition
↓
Depth-referenced processing
↓
Dielectric, energy, frequency, conductivity-related & correlation responses
↓
Lithology / material interpretation
↓
Boundaries + target intervals
↓
Vertical Virtual Borehole log
Measure the formation from inside a physical well.
Physical drilling
↓
Wireline / LWD / core measurements
↓
Gamma, resistivity, density, sonic, neutron and other logs
↓
Lithology / fluids / formation interpretation
↓
Vertical physical well log
| Conventional surface geophysics | ADR Virtual Borehole | Physical borehole petrophysics | |
|---|---|---|---|
| Acquisition | Surface / airborne / marine | Surface | Inside a physical borehole |
| Typical product | Maps, sections, anomalies, inversions, 2D/3D property models | Vertical depth-referenced Virtual Borehole | Vertical well logs with depth |
| Measurements | Method-specific physical-property response | ADR dielectric and spectral/energy/correlation response parameters | Formation responses measured directly from the borehole environment |
| Lithology interpretation | May be inferred from geophysical properties | A principal Virtual Borehole objective | Interpreted from multiple logs, cuttings/core and geological control |
| Needs drilling to acquire? | No | No | Yes |
| Physical sample? | No | No | Available where drilling/core/cuttings provide it |
| Assay / direct grade? | No | No | Requires physical sampling and laboratory assay |
| Best calibration | Geology and borehole control | Independent drilling, logs, assays and known geology | Core, cuttings, tests and laboratory measurements |
Detailed comparison
Virtual Borehole vs major exploration methods.
These are broad method characteristics, not universal specifications. Actual depth, resolution and performance depend on geology, target properties, acquisition design, noise, processing and interpretation.
| Method | Primary response | Typical role | Depth / geometry | Particular strength | Important limitation | Relationship to ADR |
|---|---|---|---|---|---|---|
| GPR | High-frequency EM reflections / dielectric contrasts | Shallow utilities, archaeology, stratigraphy, voids | Usually shallow; high spatial resolution in favourable ground | Detailed shallow imaging | Conductive/clayey/saline ground can strongly attenuate signal | Complementary where a project spans shallow high-resolution and deeper depth-referenced questions |
| IP / Resistivity | Chargeability / electrical resistivity | Minerals, alteration, groundwater, structure | Profiles and 2D/3D inversions; depth depends on array and ground | Established electrical-property mapping | Non-unique inversion; anomalies need geological interpretation | Useful independent electrical evidence against which ADR intervals can be compared |
| EM / TDEM | Electrical conductivity | Conductive sulphides, groundwater, cover, structure | Airborne/ground; shallow to substantial depth depending on system/target | Efficient conductivity mapping and conductor detection | Conductive cover and complex geometry can complicate interpretation | Can screen broad areas before targeted ADR stations |
| MT / AMT | Natural electromagnetic fields / resistivity | Deep crustal structure, geothermal, basin architecture | Hundreds of metres to kilometres and deeper | Deep regional resistivity structure | Resolution is scale/frequency dependent; inversion is non-unique | MT can establish deep structural/resistivity context; ADR can interrogate selected locations as Virtual Boreholes |
| Seismic | Elastic-wave velocity / impedance contrasts | Structure, horizons, faults, stratigraphy | 2D/3D imaging from shallow engineering to many kilometres | Detailed structural imaging | Acquisition, access, processing and interpretation can be costly/complex | Seismic geometry plus ADR material-property evidence can provide independent views of the same target |
| ADR Virtual Borehole | Processed coherent pulsed EM / dielectric and related response parameters | Depth-referenced lithology/material interpretation, fluids, boundaries, target intervals | Point-based depth profile; project-specific depth capability | Surface-acquired “borehole-style” depth interpretation at a selected location | Interpretive rather than physical sampling; conductive conditions and weak dielectric contrast can limit usefulness | Designed to integrate with existing geophysics and guide the next physical test |
| Physical Borehole | Direct samples plus logs / assays / tests | Ground truth, resource definition, reservoir testing | Narrow physical path at chosen location | Direct observation and sampling | Cost, time, access, footprint and sparse spatial coverage | Validates the Virtual Borehole and remains the final arbiter |
What makes the product different?
A Virtual Borehole is a product format — not a claim of x-ray vision.
Surface acquired. Depth referenced.
VEXRAD processes ADR measurements into a vertical, depth-referenced interpretation at a selected surface location. Depending on evidence and calibration, outputs can include interpreted lithology/material changes, formation boundaries, target intervals and confidence/evidence classification.
Direct evidence. Narrow footprint.
A drill hole physically samples the ground and can provide core, cuttings, assays, wireline logs, hydraulic tests and other direct measurements. It is not interchangeable with a Virtual Borehole.
The objective: use surface evidence to improve where, why and when that expensive physical test is made.
Integrated exploration
The strongest programme is usually a sequence, not a contest.
Where ADR can add most value
Use the method where its information changes a decision.
Existing geophysics, uncertain drill target
You already have gravity, magnetics, IP, EM, MT or seismic anomalies. ADR can be assessed as another independent data channel at selected target locations.
Existing drill control
Known geology and logs can provide calibration and an explicit validation framework before extending interpretation into untested ground.
Expensive next hole
Where the next physical borehole carries material cost or access consequences, another pre-drill evidence layer may have high decision value.
Evidence
How should a Virtual Borehole be judged?
Predict, then compare.
At Charters Towers, VEXRAD’s published case study reports an ADR anomaly at 467.91 m followed by drilling that intersected a narrow high-grade gold-bearing zone at about 463 m. The physical hole supplied the answer.
Compare against real well logs.
In Denmark, ~4 km ADR Virtual Boreholes were compared with deep-well lithology. VEXRAD reports blind cross-validation of its sand classifier against log-derived sand content at r = 0.89.
Method selection
Which method should I use?
Start with the geological decision, target property, expected depth and existing evidence. Then choose the method—or combination—that can genuinely discriminate between competing interpretations.
Choose established conventional methods when…
- You need broad regional screening or continuous 2D/3D coverage
- The target has a strong known magnetic, density, conductivity, chargeability or seismic contrast
- A mature workflow already answers the project question well
- ADR would not add a decision-relevant independent measurement
Assess ADR when…
- You need depth-referenced information at selected target locations
- Existing geophysics leaves competing geological interpretations
- There is useful drill/log control for calibration or validation
- The next physical borehole is expensive enough that additional evidence could change the decision
Frequently asked questions
Virtual Borehole comparison FAQs
Is a VEXRAD Virtual Borehole a replacement for a physical borehole?
No. It is a surface-acquired, depth-referenced interpretation intended to inform the decision before physical drilling. The physical borehole provides direct samples and remains the ground truth.
Is ADR better than seismic or magnetotellurics?
That is not a useful universal comparison. Seismic, MT and ADR respond to different physical properties and survey geometries. The right choice depends on the target and decision. They can also be complementary.
How is ADR different from GPR?
Both involve electromagnetic behaviour, but the acquisition, frequencies, processing, intended depth range and output products differ. GPR is widely used for high-resolution shallow reflection imaging; VEXRAD ADR is processed into depth-referenced Virtual Borehole interpretations for selected locations.
Can ADR be combined with existing geophysics?
Yes. VEXRAD’s preferred role is as an additional evidence layer integrated with geology, drilling and methods such as seismic, MT, EM, IP/resistivity, gravity and magnetics.
How do I know whether ADR is suitable for my project?
Suitability depends on target properties, depth, geology, ground conditions, existing data and the decision to be made. VEXRAD’s Project Fit Check is designed to assess that before a survey is proposed.
Use the right evidence for the decision.
Already have geophysics? Bring us the unresolved target.
VEXRAD can review your geology, drilling and existing geophysical evidence and assess whether an ADR Virtual Borehole could add useful independent intelligence before the next physical test.