The Earth hosts an abundance of resources that are required for day-to-day living, from groundwater and petroleum to gold and platinum. To access these resources, various applied geology techniques such as geological mapping, the application of advanced geophysics, and exploration drilling are used to assess the surficial and subsurface structures of the Earth’s crust, where these resources are found. The various phases of investigations are discussed below, from desktop assessments to exploration drilling.
Literature Review and Desktop Assessment
A literature review is the preliminary stage of an investigation. This involves collating relevant scientific articles, journals, maps, etc. to gather background information on a targeted area. The review helps geologists in the desktop assessment to identify areas which are favourable for further resource exploration.
The desktop assessment determines the geological characteristics of the target area through a review of existing geological, hydrogeological, and topographic maps, existing data (e.g., borehole logs, downhole geophysics, etc.), remote sensing, and available Digital Elevation Models (DEMs).
A field investigation follows the desktop assessment, depending on the level of assessment required, either to confirm or update the findings of the desktop assessment by gathering extra information on an area. Field mapping is a key form of investigation to any geological exploration and is described as the process of identifying surface geological, hydrogeological, and hydrological features of an area. These features aid in identifying potential resources typically found in the subsurface. Field mapping data includes:
- Structural features (fractures, faults, folding, etc.)
- Compass measurements (direction and orientation of planar and linear features such as joints, fractures, bedding planes, faults, fold limbs, etc.)
- Lithological descriptions (rock types, geological formations, etc.)
- Seep locations.
The data collected from field mapping is used to produce geological and hydrogeological maps and cross-sections which are then interpreted to target favourable positions for resource exploration. The figure below shows how geological mapping was used to identify favourable positions for groundwater abstraction from the Peninsula Aquifer in the Oudtshoorn area, producing artesian yields greater than 40 litres per second.
Field mapping along the Doring River to identify favourable locations to access the Peninsula Aquifer for groundwater exploration.
Geophysics is a non-invasive investigation of the Earth’s subsurface conditions through measuring, analysing, and interpreting physical property variations. These investigations use various seismic, magnetic, gravity, electrical, and electromagnetic methods in search of water, gas, oil, and minerals. Geophysical techniques, such as airborne geophysical surveys, can be applied to exploration in areas which are not easily accessible on foot, are large in size, or they can be used in conjunction with other exploration techniques to focus on a targeted resource.
Typical geophysics methods used in resource exploration include:
- Airborne geophysical surveys
- Gravity surveys
- Deep seismic reflection surveys
- Seismic refraction surveys
- 2D and 3D seismic surveys
- Magnetotellurics surveys
- Downhole geophysical surveys (and types of data that can be acquired at the borehole) include:
- Natural gamma radiation
- Borehole diameter
- Total porosity
- Free fluid volume
- Clay-bound fluid volume
- Capillary bound fluid
- Hydraulic conductivity.
Once an area has been deemed favourable following the initial stages of investigation, exploration drilling is used to explore sites for potential geological, hydrogeological or commercial value. Geologists can study extracted core/drilling material and conduct lithological, hydrogeological, mineralogical, petrologic, and structural analyses.
Depending on the geology and the intended outcome of the drilling, different drilling techniques are used, which include:
- Auger drilling
- Sonic drilling
- Rotary mud drilling
- Diamond drilling
- Coiled tubing drilling
- Reverse circulation (RC) drilling
- Percussion drilling.
Exploration drilling allows geologists to obtain information in three dimensions. The geological and hydrogeological data acquired feeds into the conceptual and or subsequent numerical model depending on the level of confidence of the study, e.g., numerical models have been developed for the City of Cape Town’s Groundwater Schemes due to their scale and importance. Ultimately, the data and information gathered from drilling informs future decision-making.
- Groundwater exploration
- Petroleum exploration
- Geothermal exploration
- Mineral exploration
- Geotechnical investigations.
Umvoto has a team of specialists with skills and expertise in Applied Geology including structural geology, sedimentology, borehole supervision, core logging, geochemistry, mine dewatering, and geostatistics. Umvoto also has a team of highly trained GIS specialists able to use remote sensing to map complex terrains and conduct monitoring of earth processes. Our experience reaches nationally and internationally – South Africa, Namibia, Mozambique, Zambia, Ethiopia, Malawi, Tanzania, Eritrea, Ghana, Kazakhstan, and Saudi Arabia.