The “microseepage” of oil in the region led to the government commissioning a survey to see if it was commercially viable to extract petroleum.
By Larry Claasen
THE Department of Mineral Resources and Energy is investigating the extent of petroleum resources of the Karoo for possible extraction.
The department approved a survey to assess the extent of “petroleum and assess any potential geological risks related to the exploration for and the production of petroleum” in the southern Karoo Basin, in the government gazette late last year.
Though the government has long seen the extraction of shale gas in the region as a way to increase energy independence, the move to assess the scale of possible petroleum deposits is new following the recent discovery of “microseepage of oil in the basin.”
The survey, which will be conducted in parts of the Western Cape, Northern Cape and Eastern Cape will be carried out by the Petroleum Agency of SA. It will consist of 2 246-line km of 2D reflection seismic surveys, 21 253-line km of airborne magnetic and radiometric surveys, and approximately 2 318 magnetotelluric stations, which will be deployed along the seismic profiles.
The department says the data obtained from this investigation will enable it to make informed decisions regarding the issuing of exploration rights in the area.
The survey is needed because the data collected between 1966 and 1971, by the former South African national oil company SOEKOR, was outdated and of poor quality.
The new surveys will utilise advanced techniques, including vibroseis trucks, generate energy at 20 m interval offroad along roadside, and wireless nodal technology, to minimise environmental impact while delivering precise data.
The aeromagnetic/radiometric survey will be conducted using an aircraft with an attached magnetometer and installed spectrometer.
“As the aircraft flies, the magnetometer measures and records the total intensity of the magnetic field at the sensor. This measurement includes the desired magnetic field generated in the Earth as well as tiny variations due to the constantly varying solar wind and the magnetic field of the survey aircraft.”
The aeromagnetic/radiometric surveys will be flown on a grid basis along survey lines with further perpendicular (tie) lines. Data will be acquired at 1 km line spacing, and the flight height will be 50 m Mean Terrain Clearance above ground level.
The Magnetotelluric (MT) surveys are a passive geophysical method that uses natural electromagnetic fields to investigate the electrical conductivity structure of the earth from 100’s of metres to 100’s of km depth below ground surface.
No disturbances to land and infrastructure are expected and any impact on people during operations is expected to be minimal to nil.
The land within the defined area consists of State-owned land, privately owned farmlands, commonage land, and communal land managed by tribal authorities.
The identified sensitive areas such as National and Provincial parks, and wetlands are excluded in the investigation.
The survey results will also inform the geo-environmental baseline research initiatives underway, such as implementation of a groundwater monitoring network, well risk integrity assessments and seismicity monitoring network.
The study will assist with the “identification and delineation of areas” that may be too risky from an environmental point of view and should therefore be excluded from shale gas development.
