A Holistic Approach (if you can’t measure it then you can’t manage it)
As our available fresh water becomes increasingly scarce and valuable many are calling groundwater the new oil. Airborne geophysical methods have been used for decades in oil exploration, however, unlike the oil industry, few governments are mapping water in a systematic way. SkyTEM advanced the technique and engineered the airborne method that now makes it possible to map water resources efficiently and effectively.
Hidden in aquifers, groundwater is a body of permeable and porous saturated rock and intricate networks of buried river channels through which water moves. Mapping and protecting this hidden resource is a challenging task. To begin to manage groundwater effectively and sustainably dependable, accurate, high-resolution subsurface data must be collected and used to monitor and manage. SkyTEM data is proven and reliable and has been used to measure:
- groundwater levels within groundwater basins
- groundwater quality degradation
- land surface subsidence
- changes in surface flow and surface water quality that directly affect groundwater levels or quality
- changes in surface flow and surface water quality that are caused by groundwater pumping
SkyTEM data is accurate, robust, reliable and results closely correlate with borehole or ground truth data. The geophysical data collected does not replace, but complements existing borehole data, thereby reinforcing the geological interpretation, which in turn leads to greater certainty of identified economical and productive targets. Once the area has been mapped with SkyTEM, the data can be interpreted for other targets as well, including location and extent of salt water encroachment, groundwater recharge areas, surface and groundwater connections, contaminant plumes and inputs for geotechnical and environmental engineering studies such as mine tailing site selection.
Hydrogeological Mapping in Northeastern British Columbia
In 2015 Geoscience BC (GBC) launched the Peace Project – a subsurface mapping project designed to collect new information about groundwater within an 8,000 square kilometer area in northeast BC, Canada. This region of the province has been a focus of petroleum exploration and development since 1952 and participating partner companies included the BC Oil & Gas Commission, ConocoPhillips and Progress Energy as well as several Treaty 8 First Nations.
The figure below shows SkyTEM airborne results (left) and gamma log borehole results (right). The paleochannel in the area lies at about 10 meters depth and is about 50 meters deep as mapped by SkyTEM. The gamma results show the depth to bedrock at each well (numbers near red and yellow dots – yellow dots indicate sand/gravel). Note the outline of the paleochannel as interpreted from the borehole data and how it matches the airborne electromagnetic (AEM) results. These two data sets were done independently and neither processing group saw the other’s results. Conclusions from the comparison of airborne and ground geophysical data are:
- the airborne data is in good agreement with the drilling data;
- many holes were drilled at various depths to delineate the aquifer. Several were far from the paleochannel;
- the airborne data was collected in a few minutes whereas the drilling required many months;
- no dollar figures for the drill program are available but given the time and money required to drill approximately 24 holes it is expected the airborne data was significantly less expensive to obtain;
- to save time and money and increase the changes of striking water, it is highly recommend that SkyTEM data is collected in order to select and optimize drill targets. This drill data can then be used for verification and further refinement of the airborne data interpretation model.
Rigorous analysis and accurate geological interpretation of SkyTEM data is possible as SkyTEM is the only system calibrated at the Lyngby test range in Denmark. This allows for direct comparison with previous SkyTEM and ground based or borehole EM datasets together with complete traceability back to the Lyngby TDEM reference model.
Over the last 10 years SkyTEM has been selected to map large portions of the State of Nebraska. A paper by Jared D. Abraham(Aqua Geo Frames) at the AEM 2018, describing SkyTEM results from a hydrogeolical mapping program in Nebraska said “The staggered pace of investigation has occurred because of the finite resources that can be allocated to AEM data gathering and the dynamic needs of the NRD’s within Nebraska. This has led to the requirement that the systems be well calibrated and that the inversions be able to be integrated together to provide an evolving picture of the hydrogeological framework in Nebraska.” Please find the full paper here.
The nature of both SkyTEM’s frame and the hardware means that the raw data is well-calibrated (i.e. system bias is below background noise level and there is negligible drift). The receiver coils are placed so as to be null-coupled to the primary field of the transmitter, in order to minimise the self-response of the system. The bias signal from the transmitter is very low, meaning that regular excursions to high altitude to monitor the bias response are not necessary during each flight. In terms of applications and benefits to customers, that means:
- Data can be processed and inverted in the field, allowing rapid assessment of survey results and planning of infill lines whilst a survey is in progress;
- This preliminary EM data, delivered within 48 hours of acquisition, is very similar to final office-processed data;
- No levelling of the electromagnetic data is required between flights or infill campaigns Surveys done at different times and with different SkyTEM instruments can be seamlessly stitched together. This gives the option of flying multiple systems concurrently on large surveys for faster completion of acquisition.
Find high yield sites to drill
SkyTEM can be compared to computed tomography (CT) scans performed on the human body as it is a non-invasive way to diagnose or flesh out geological features and conditions in three dimensions. The technology delivers digital data that is used for creating detailed 3D geological representations used for a variety of different applications and are a vital factor for designing reliable and practical hydrological models for sustainable water management.
Principal research scientist Richard George, Department of Agriculture and Food, Australia says drilling involves a hit-and-miss technique in which there is just a one-in-five chance of finding water and even less chance of finding water of suitable quality. He also states a SkyTEM survey has doubled the odds of striking it lucky. “We’re running better than a one-in-three success rate of finding sufficient water-bearing sands, though we’re still only half way through the program. By finding sites with high yield we can save on energy as we don’t have to pump from such a long way down.”
The superior mapping capabilities of SkyTEM Surveys are well documented in papers and case studies authored by our clients and the scientific community. More resources can be found here.
SkyTEM systems are rigid, dynamic, and capable of collecting reliable data at the fastest helicopter acquisition rate possible in the industry. SkyTEMFAST remains straight and level during high-speed flight benefiting data quality as well as survey efficiency and economy. Data is collected at speeds of up to 150kph with a late time gate of 15ms and 500,000 NIA to maximize depth of penetration. This system is ideal for large regional surveys and data collection over level terrain, with low terrain clearances , combined with the ability to drape fly. The helicopter platform also offers logistics flexibility, potentially lessening the need for long refuel ferries.
For budgetary reasons alone, large-scale airborne surveys have traditionally employed fixed-wing aircraft (FWTEM) platforms. This, however, has often been at the expense of near-surface resolution due to the separation between the transmitter and receiver of fixed wing systems and the requirement to fly at higher altitudes and faster speeds than helicopter-borne electromagnetic (HTEM) systems. As a result ground geophysical surveys are often required to followup the targets detected by fixed wing systems. With SkyTEMFAST as a helicopter platform the geophysical surveys benefit from the ability to operate from remote locations and there is no requirement for a landing strip or airport as there is for Fixed Wing surveys.
CSIRO Compares the SkyTEM312, SkyTEM312FAST and VTEM
Geoscience Australia conducted field tests to compare results of three helicopter-borne systems, the SkyTEM312, SkyTEM312FAST and a non dual moment system. The published conclusions can be found at http://www.publish.csiro.au/ex/pdf/ASEG2016ab302. They include “At depth there is very good agreement between the three systems” but “SkyTEM systems have a better resolution in the top 30m.” The paper states that this near surface resolution is not seen in the other system. The ability of SkyTEM to detect the more subtle resistivity contrast due to the geological structure above a deposit is significant in that it may represent an exploration indicator for the location of large deposits at depth. It also provides shallow information that can improve the accuracy of inversion or discrete target modelling results.
Geoscience BC Peace Project
Geoscience BC selected the SkyTEM312FAST system for their Peace Project – a subsurface mapping project designed to collect new information about geology and lithology within an 8,300 square kilometre area in northeast British Columbia. The Peace region of the province has been a focus of petroleum exploration and development since 1952 and participating partner companies included the BC Oil and Gas Commission, Conoco Phillips and Progress Energy as well as several Treaty 8 First Nations.
The main priority of the project was to map the area, comprising some 21,000 line kilomtres, in fine detail to a depth of at least 300 metres. In addition, a major project planning constraint was that the airborne data acquisition had to be completed before the hunting and trapping season began. This required the project to be completed within seven (7) weeks from start up. In order to meet this tight deadline, SkyTEM312FAST was selected for data acquisition. Over 1,000 line kilometres of data were often collected during a single day, unprecedented in HTEM surveys, with total coverage completed in only forty-three (43) days, well within the time frame required.
While the initial objective was to map to at least 300m, SkyTEM312FAST resolved geology in some areas to depths approaching 500m.
For more information on the Geoscience BC Peace Project, please visit their website.
“I had the opportunity to perform QA/QC checks on SkyTEM’s preliminary data and found it to be consistent and of high quality. SkyTEM maintained excellent communication with me throughout data acquisition and delivered the data electronically in a time fashion required in the contract”
~Dr. Mel Best, President
Bemex Consulting International
“SkyTEM312FAST is an incredibly efficient system, and we are impressed by the great results we have achieved so far. Not only does the SkyTEM system map the near surface we were looking for, it now seems the system has a much greater depth of penetration than we expected for resolving much deeper geology. The ability to review high quality data several times a week was also a benefit to our program”
~Carlos Salas, Vice-President