Geophysics Analysis & Interpretation

Mapping Groundwater  

Our approach is to translate the geophysics to usable geology/hydrogeology information. 
TerraNotes has developed a number of technologies to discover and map aquifers using airborne electromagnetic surveys data. 
This workflow and technology produces high resolution maps of aquifers at regional or local scales. 
Airborne geophysical surveys for groundwater projects have proven effective and successful. The time domain electromagnetic (EM) surveys gather resistivity data from the upper 0–400 meters to help map the regional and local aquifers and the geologic structures that control ground water flow. 

In addition, the surveys acquire high resolution magnetic data, which are used to reveal the network of faults and fractures in the crystalline rocks forming the basement and in the sedimentary above. 
The magnetic data can also be used to estimate depth-to-source of the crystalline basement rocks.  The thickness of sediments bears significantly on the hydrology of the basin, as shallow crystalline basement may interfere with water flow.

The map below shows an area ~300 km long and ~150 km wide where an airborne survey was conducted. 
The green ellipses show the zones with the highest potential for aquifers.

                                                                                                                                 Mapping of Paleo Channels


This type of survey delivers the following items:

  1. Maps of the resistive zones in 2D and 3D
  2. Maps of groundwater/surface water networks and channels
  3. Maps of groundwater flow and transport
  4. Geological maps surrounding the aquifers
  5. Mapping of lineaments and other structures such as faults, dykes, intrusions, shear zones, etc.
  6. High resolution maps display the structure and anomalies’ boundary, edge and contacts
  7. Depth Estimations: TerraNotes uses a number of depth estimation techniques including inversions to ensure greater validity of the results
  8. Ternary maps for enhanced visualization of combined anomalies in one map
  9. Porosity and permeability assessment and mapping

TerraNotes CRI Index
The Composite Resistivity Index (CRI) is a TerraNotes proprietary technique used to integrate and calibrate airborne surveys with well logs or drillholes data.

One of the advantages of this CRI technique is that it provides greater certainty about what the airborne survey truly measures. 
Secondly, this technique allows for the production of more reliable maps of the aquifer zones, and models of the resistivity variations at depth. It also provides more reliable assessment of the depth and thickness of aquifers.

As you are aware, the only way to know for sure what’s being measure in geophysics is by ground truthing with drillholes. To achieve that objective without drilling new holes, we developed a method that we call CRI (Composite Resistivity Index) to map the aquifers and potential zones for aquifers. 

Mapping Groundwater/aquifers with the TerraNotes CRI Index

The Composite Resistivity Index (CRI) is a TerraNotes proprietary technique which is applied to calibrate time-domain electromagnetic (TDEM) survey data using Oil and Gas borehole logs.

The resulting products include maps of the extent, depth and thickness of aquifers and potential zones for aquifers, as well as  3D imaging of the aquifer zones and 2D-3D models.

These products allow for the delineation and depth estimates of aquifers and their related geological environment without additional drilling.

Some of the benefits of the CRI approach include the following:

  1. Improvement of the delineation of the zones of potential aquifers with improved definition of their edges compared to conventional airborne survey processing.
  2. The method helps interpret and differentiate the types of potential aquifers throughout the survey area, as well as heterogeneity within each aquifer zone.
  3. The CRI-based maps provide more details of resistivity variations compared to traditional inversion or RDI sections alone (Resistivity Depth Imaging).
  4. The CRI maps provided resistivity variations of local details within the anomalies - which could then be correlated with local lithology and other geology information. With this systematic integration the constraints into the inversion we can construct a geologically meaningful physical property model of the each aquifer zone.
  5. The data provided by Time Domain EM (or Frequency Domain EM) combined with the TerraNotes technology for enhanced mapping and the TerraNotes CRI calibration were sufficient to locate and map aquifers and other groundwater-related bodies to a depth of up to ~ 800 meters below ground level (depending on the geology) in the Calgary-Edmonton corridor.
  6. This approach was also very effective at measuring sand and gravel lenses of thickness of ~10 meters.
  7. This method was particularly useful and effective in the areas where there is no stratigraphic context.

The process involves stratifying the oil and gas logging curves including Resistivity and Porosity logging. The CRI index for the boreholes and for the EM decay (Geotem, SkyTEM, etc) are then calculated. The boreholes CRI are then used to calibrate the TDEM CRI for flight lines crossing and surrounding the drillholes, and iterates such process to the entire survey area of the property flown. Finally, the calibrated TDEM results are mapped and used to delineate the aquifer zones. Inversions and modeling are then produced using those constraints.

In summary, this technique integrates drillholes data with the airborne electromagnetic data . This allows for constrained inversion to improve the geological model of aquifer zones. It also produces more reliable maps of the regional and local aquifer zones and the zones' own variations of resistivity. 

There are also environmental advantages in having precise delineation of aquifers in the 3 dimensions to mitigate the risks related to management of drilling, agriculture and forestry activities.

Typical imaging produced for such project.

On the CRI map below red and yellow colors represent aquifers as later proven by test drilling.
The CRI maps provides well defined edges of anomalies. The CRI map provides resistivity variations of local details within the anomalies - which can be correlated with local lithology and other geology information.

After conducting this project, it was concluded that the data provided by Time Domain EM (or Frequency Domain EM) combined with the TerraNotes technology for enhanced mapping and the TerraNotes CRI calibration are sufficient to locate and map aquifers and other groundwater to a depth of up to ~ 800 meters below ground level (depending on the geology). 
This approach can also measure sand and gravel lenses of thickness of ~10 meters or more.

Mapping Subsurface Contaminants Plumes Due to Spills or Leakages

TerraNotes has developed a technique and workflow that combines the High Density Resistivity System and the LIF System (Laser Induced Fluorescence).

Once the contamination anomalies have been mapped with the TerraNotes Geoeletrical system, we test and characterize the chemical compound of the anomalies with the LIF or the MIP system. This system allow us to provide to you a very detailed characterization and volume size of the anomalies. 
Click here for more information about the LIF and MIP systems.

TerraNotes has developed one of the world’s largest smart-electrode geoelectrical survey systems with 120 computer-connected electrodes. This system scans the property and maps subsurface features with high resolution.

The main advantage of this approach is that this process scans the field in such a way that it provides a much higher density of data points. On a typical well site, we get over 30,000 data points. How many boreholes would realistically have to be drilled to obtain a similar number of data point?
Compared to EM31-38 or GEM2, the TerraNotes High Density Geoelectrical system provides much higher resolution and less error; produces imaging in 3D of the earths layers and contamination anomalies; has a more advantageous signal to noise ratio.

Our services have shown to:

  1. Cut costs of contaminant delineation - by reducing the number of test boreholes
  2. Cut costs of hydro and chemical testing
  3. Work in sensitive environmental conditions - due to the low footprint of our survey system
  4. Reduce remediation time
  5. Accelerate the reclamation process

The map above shows the distribution of subsurface contamination plumes in 3D.                   The maps above show the direction of flow of the contamination

This not a model, this is the direct imaging of the resistivity data collected in                           based on integrated resistivity and hydrogelogy measurements.

the field.



The panel below shows geoelectrical profiles at an abandoned well site. 
The TerraNotes geoelectrical survey showed a contamination anomaly visible on the panels below. 
Subsequently, test drill holes were drilled around that anomaly and 4 holes encountered contamination directly surrounding the anomaly. No contamination was encountered in holes further away from the anomaly

                   Site scan area                                                        2D resistivity                                                                    3D plume

•  3D subsurface contamination delineation
•  3D visualization and analysis of plumes
•  Size, shape, geometry, & volume of plumes
•  3D imaging of contamination migration paths
•  Finds the source of contamination
•  Mapping soil and geological layers
•  Mapping drill locations

•  3D groundwater flow and contaminant transport
•  4D subsurface characterization
•  3D saltwater intrusion monitoring
•  Porosity and permeability assessment and
•  3D imaging of multiphase flow and transport 
•  3D imaging of groundwater networks

•  Detection and 3D mapping of leak plumes and subsurface sources

Since 2007, TerraNotes Ltd has combined its technology with expertise and teamwork to deliver 3D site characterization to customers in Canada/US in oil and gas, oilsands industries, electrical power and water utilities, engineering firms and government departments.