Implementation

 

Borehole radar can be used to map out structures and lithology contacts surrounding your drillhole. Some examples of applications are:

  • Map prospective lithology contacts
  • Map intrusives, e.g. porphyrys
  • Map complex structures e.g. splays
  • Map quartz reefs
  • Map out hazards that can affect mining.

The correct implementation of borehole radar is important to ensure that your objectives are met. This section outlines some of the important things to consider when implementing borehole radar at your mine site or exploration project. We recommend you contact GeoMole for more information if you are considering borehole radar at your site or project.

Your Rock Types and Trial Surveys

The host rock of your deposit is important for BHR surveys. The rock needs to be sufficiently transparent to radar waves to enable the signal to penetrate through the rock and bounce of a lithology contact or structure and return back to the radar receiver. The properties of the target structure or contact are of secondary importance. There must be a dieletric change at the contact and the contact must be relatively sharp for a clear reflection. It is well known that conductive rocks reflect radar energy well and with a strong amplitude, however non-conductive interfaces also reflect radar energy. Borehole radar's usefullness is not limited to conductive orebodies.

Radarwave propogation works well in hard resistive rocks. Examples of host rocks that work well (range > 30m) for Borehole Radar are:

  • Granite
  • Basalt
  • Ultramafics
  • Norite
  • Anorthosite
  • Dolomite
  • Limestone
  • Peridotite
  • Porphyry

This list only includes rock-types that have been successfully tested with the GeoMole BHR. Contact GeoMole to get an estimate of how well radar will perform at your site. Sedimentary rocks, such as sandstone, don't perform as well as hard igneous rocks, with an estimated range in sandstone of 15m. 

GeoMole can run a trial survey to determine if Borehole Radar will work at your site.

Borehole Planning

The orientations of the drillholes are important for borehole radar surveys. The drillhole has to be at such an angle to the target horizon to enable a reflection to be imaged from it. Normal drill planning has holes orientated perpendicular to the target horizon. By changing the orientation of at least one hole in the drill plan section, borehole radar can image discontinuities between the other drillholes.

Optimal Drillhole LayoutDrillholeLayout

Figure 1: Optimal drillhole layout and relative to a drill program.

Acquisition: Wireline vs Drill-deployed

GeoMole has developed a method of deployment which is unique to downhole geophysics, but very common in the mining industry; Pump-down and Push-down tool deployment. Borehole radar can still be surveyed on a traditional wireline in needed, however GeoMole have found that the pump-down survey is often quicker and enables unstable holes to be surveyed. The pump-down method also enables horizontal and upholes to be surveyed with borehole radar.

The borehole radar pump-down procedure is similar to a multishot EMS trajectory survey or GYRO survey. The probe is attached to the core barrel and then pumped to the end of the rods and out through the bit. The rods are then pulled and the radar surveys the entire length of the hole while it is being pulled back up.

Pump-down radar

Figure 2: Schematic of Pump-down setup.

Processing and Interpretation

GeoMole conducts all of its processing and interpretation in SeisWin. Processing and preliminary interpretation can be completed within days of the BHR survey being completed. When the BHR results are crucial to an ongoing drilling campaign, data can be processed and interpreted on the fly providing information almost instantaneously for oingoing drilling.

The main processing procedures involve data resampling and recompression, 1D filtering and gain control. Interpretation procedures include forward modelling and synthesis. Multiple datasets from neighbouring drillholes can be interpreted simultaneously in SeisWin.

Using the Results

Borehole radar interpretations provide continuous strings in space for a lithology contact or structure. These string files can then be imported into your mine planning packages to use when modelling your geology. A migrated BHR section can also be imported into your mine planning packages as a georeferenced image. This enables the mine or exploration geologist to correlate the BHR reflections with known drill hole intersections for additional confidence in the results. The figure below illustrates how the radar data can be correlated with geological models.

Figure 3: Migrated section in GoCAD correlating the radar results with the resource model. Structural splays off the main horizon can be seen in the radar data.

Self-drive for your site or project

The GeoMole Self Drive product enables companies to run the GeoMole BHR system seamlessly as part of their exploration and mining process. Self Drive includes all the hardware, software, training and consulting needed to run BHR at your mine site. The cost of self drive depends on the amount of drillholes that you want to survey. Contact Geomole for more information on the Self Drive product.