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Earth Explorer is an online source of news, expertise and applied knowledge for resource explorers and earth scientists. Sponsored by Geosoft.

News & Views

News Archive

December 7, 2016

Geosoft introduces IP and resistivity inversion in VOXI Earth Modelling

Geosoft has added induced polarization and resistivity data inversion to its VOXI Earth Modelling 3D inversion software service. Geoscientists are now able to create detailed 3D models of conductivity and chargeability from IP and resistivity survey data with VOXI. The resulting models can assist in interpreting and targeting regions for mineral and environmental applications...

December 5, 2016

Mexico's Deepwater Round Exceeds Expectations

Some of the world's biggest oil companies showed up Dec. 5 and agreed to invest on the Mexican side of the Gulf of Mexico, proving that deepwater exploration still has a pulse despite challenging market conditions...

November 30, 2016

Magnetic inversion results for Ngamiland available for download

A regional-scale geophysical inversion of magnetic field data in the Ngamiland region of northwestern Botswana is now available for download from the Botswana Geoscience Portal, a partnership initiative of the Botswana Geoscience Institute, industry sponsors and Geosoft...

November 30, 2016

LIGO Resumes Search for Gravitational Waves

After a series of upgrades, the twin detectors of LIGO, the Laser Interferometer Gravitational-wave Observatory, have turned back on and resumed their search for ripples in the fabric of space and time known as gravitational waves. LIGO transitioned from their engineering test runs to full science observations at 8 a.m. Pacific Standard Time on November 30...

November 9, 2016

International Volcano Scientists Unite

For the first time, the United States will host the international Volcano Observatory Best Practices workshop, previously held only in Italy. The workshop will take place this month in Vancouver, Washington. It is designed specifically for volcano observatories around the world and their staff to exchange ideas and best practices with each other...

October 4, 2016

USGS Assesses Mineral Potential for Sagebrush Habitats in Six Western States

USGS has completed a comprehensive assessment and inventory of potential mineral resources covering approximately 10 million acres of Federal and adjacent lands in Idaho, Montana, Nevada, Oregon, Utah and Wyoming...

October 3, 2016

Uganda Targets Up to U.S.$100 Million for Mineral Exploration

Uganda is well endowed with mineral resources and, like many naturally-gifted African countries, is becoming keen on ensuring that these resources play a transformative role in its long-term structural transformation dream - the Vision 2040...

September 9, 2016

Small-Scale Fishers Get A Big Boost With First-Of-Its Kind Impact Investment Fund

Conservation organization Rare announces the Meloy Fund for Small-Scale Fisheries at Our Ocean Conference. The Global Environment Facility, one of the largest funders of conservation worldwide, will be investing $6 million into the fund...

September 1, 2016

Scientists take to the skies to track West African pollution

Scientists operating research aircraft over West Africa have detected organic materials in the atmosphere over a number of urban areas, contributing to concerns of the rise in pollution across the region...

August 17, 2016

New IGS Xplore prospectivity maps for Botswana

International Geoscience Services have released a series of base metal prospectivity maps for the Ngamiland District of northwestern Botswana using free geodata available on the recently-launched Botswana Geoscience Portal, hosted by Geosoft. The maps identify favorable areas for copper, zinc and lead mineralization using geological, geochemical and geophysical datasets downloaded directly from the portal.

August 11, 2016

NexGen Makes New High Grade Discovery

NexGen Energy reported the discovery of a new high grade zone of mineralization 4.7 km northeast of the Arrow Deposit as part of an on-going summer drilling program on its 100% owned, Rook I property, Athabasca Basin, Saskatchewan...

August 10, 2016

Rampion UXO Disposal to Take Place This Week

E.ON has confirmed that the two unexploded devices, detected along the Rampion offshore cable route will be safely disposed this week following the consultation with the Marine Management Organisation...

August 9, 2016

Diamonds In The Rough: E&Ps Find New Reserves In Mature Basins

The oil industry’s history demonstrates clearly that new plays and prospects have long been found in mature basins that were thought to be well on the way to being squeezed dry. Through the acquisition of new data, developing new concepts and coming up with fresh interpretations, long-producing basins around the world from the North Sea to Malaysia have continued to reveal new riches...

August 8, 2016

Northern Shield Identifies High Quality VTEM Targets at Séquoi

Northern Shield Resources announced the results of the interpretation and modelling of the VTEM survey from the Séquoi Property in the Labrador Trough of Quebec . Séquoi is owned 100% by Northern Shield and is being explored for Noril'sk style Ni-Cu-PGE massive sulphides. After geophysical modelling and interpretation of the VTEM data from Séquoi, six VTEM anomalies of significant interest have been identified...

August 3, 2016

Rio Tinto tailors big data drive to copper

Rio Tinto will put the weight of an exploration big data push and its newly-formed Growth and Innovation group behind its desire to identify a "tier 1" copper asset. Speaking at the annual Diggers & Dealers conference in Kalgoorlie, Growth and Innovation group executive Stephen McIntosh said Australia was "overdue for a tier 1" mineral discovery of any type...

August 1, 2016

Tetra Tech Awarded $200 Million Navy CLEAN Contract

Tetra Tech announced that it has been awarded a $200 million, single-award contract by Naval Facilities Engineering Command (NAVFAC) Atlantic. Through the Comprehensive Long-term Environmental Action Navy (CLEAN) contract, Tetra Tech will provide environmental engineering support services to installations within the NAVFAC Atlantic Area of Responsibility...

May 3, 2016

NATO Science for Peace and Security (SPS), MODUM Partners announce "Young Scientist Summer School on Sea Dumped Chemical Weapons"

This international project cooperates closely with CHEMSEA (Search and Assessment of Chemical Weapons) Project for and sharing and knowledge transfer...

April 12, 2016

Monday mad rush for gold stocks

Renewed optimism about the outlook for gold saw investors pile back into gold stocks, pushing many stock to 52-week highs in heavy volumes...

April 11, 2016

Medgold Resources: Continues to Expand the Boticas Gold Project, Portugal; Proposes $200,000 Private Placement

Medgold Resources is pleased to announce new assay results from contiguous rock-chip sampling from the Limarinho South zone at its Boticas gold project in Portugal, which include a highlight of 6.0m @ 5.7 g/t Au...

April 8, 2016

De-carbonizing our energy sector

Nuclear energy currently provides around 11 percent of the world's electricity. China, the European Union, the United States, India, Russia, South Korea, and other nations’ have major existing fleets...

April 1, 2016

Follow-Up Drilling Results Indicate Wide Gold Zones at Hendricks Gold Discovery

Gascoyne Resources Limited announced that it has received the final assay results from the 10,000 metre aircore exploration drilling programme...

March 26, 2016

The Oil Market Is Finally Hitting Its Breaking Point

After a significant reduction in investments over the past two years, oil companies can no longer overcome the production declines from legacy wells...

March 15, 2016

N-Sea Expands into the French Offshore Wind Industry

Subsea IMR provider, N-Sea, has signed a letter of intent with CERES Recherches & Expertise Sous-Marine and TechSub Industrie Environement, to provide subsea survey, installation and remediation services to the French offshore wind industry...

March 9, 2016

PDAC 2016 Convention Exceeds 22,000 Attendees

Optimism and opportunity abounded at the PDAC 2016 Convention of The Prospectors & Developers Association of Canada in spite of recent industry challenges...

March 3, 2016

6 Alpha Launches EOD Contracting Division

6 Alpha Associates, a specialist risk consultancy practice, with expertise in the assessment and management of unexploded ordnance, has launched a dedicated explosive ordnance disposal division...

Modelling the Karoo aids petroleum exploration in South Africa

The extensive Karoo Basin of South Africa may hold vast reserves of shale gas. A tectonic modelling project underway will help determine their production viability.

by Graham Chandler on March 8, 2013 applied

Geophysicist Stephanie Scheiber-Enslin is creating a tectonic model of the Karoo basin for her doctoral thesis at Johannesburg’s University of the Witwatersrand.

“Shale gas is a new hot topic in South Africa, where the main focus has previously been on mineral exploration. I wanted to do a project that is more geared towards petroleum exploration."
- Stephanie Scheiber-Enslin

[Click to enlarge]

2D gravity model extended north along Stankiewicz et al. (2007) eastern seismic profile in the southwestern Karoo basin. Upper panel shows the observed gravity field (thick black line), modelled gravity (thin black line), and error (red line). Lower panel shows a 2D gravity model with density values in determined from seismic velocity conversions. Stankiewicz et al. (2007) seismic image and SOEKOR borehole logs (circular wells) are overlain. The main feature in the gravity model is the gravity decrease as the Moho deepens further inland/north from the ocean-continent boundary. Additional bodies are needed in the crust and mantle in the 3D model to fit the measured data.


[Click to enlarge]

2D magnetic model along Stankiewicz et al. (2007) eastern seismic profile. The upper panel shows the observed magnetic anomaly (thick black line), modeled anomaly (thin black line), and error (red line). The lower panel shows a 2D magnetic model with susceptibility values in SI with Stankiewicz et al. (2007) seismic image overlain. As determined from reflection and refraction data, the body causing the Beattie anomaly (BMA) is modeled in the middle crust between ~10 and 20 km depth, with a high susceptibility value (the value given is a preliminary estimate and remament magnetisation is not included). The main magnetic body of the BMA correlates with a high seismic velocity anomaly (“BMA”, 0.13 SI), though an additional body is needed to the south where there is no seismic velocity anomaly (“Anom”, 0.095 SI) in order to fit the measured field.

South Africa is hoping to join the world’s ‘tight’ gas rush with reservoirs of its own. Regions the world over from Australia to Poland to British Columbia are discovering and exploiting these types of gas reserves, thanks to the game-changing techniques of horizontal drilling and multiple-stage fracturing.

With just 183,000 barrels per day of total oil production in 2011—which includes synthetic liquids from coal and natural gas (most of that imported)—South Africa is domestically energy-deficient. Imports averaged a further 427,000 barrels per day just to meet the country’s growing demand. This, along with rapidly increasing electricity demand, has prompted ambitious government plans to expand its energy sector.

Development of Karoo Basin gas reserves, if viable, could be the solution. An April 2011 estimate by the US Energy Information Administration puts South Africa’s technically recoverable shale gas resources, mostly in the Karoo, at 485 trillion cubic feet—over half the size of the US’s. If developed, much production would likely be slated to extend supply to the Mossel Bay gas-to-liquids plant, already the world’s largest.

But so far explorers haven’t even had a conclusive tectonic model of the basin for starters. Geophysicist Stephanie Scheiber-Enslin is addressing that: creating a model for her doctoral thesis at Johannesburg’s University of the Witwatersrand.

Her project is certainly a timely one. “Shale gas is a new hot topic in South Africa, where the main focus has previously been on mineral exploration,” she says. “I wanted to do a project that is more geared towards petroleum exploration.” Two of her doctoral supervisors (Susan Webb, of University of the Witwatersrand, South Africa and Jörg Ebbing, of the Department for Petroleum Engineering and Applied Geophysics at Norwegian University of Science and Technology and Norwegian Geological Survey) had already started some work on the project.

The project is well-supported: funding is provided by South Africa’s National Research Foundation, and administered by the Council for Geoscience. Geosoft Africa has been supporting her research by providing Geosoft software for the project over the past few years.

Her work is cut out for her. The Karoo Basin is a broad arid plateau covering much of South Africa’s interior. The plateau is supported by the stable Archean Kaapvaal Craton in the north and several surrounding Proterozoic basement blocks in the south, and formed within the continental interior of Gondwana between the Late Carboniferous and Middle Jurassic. The main basin covers about 700,000 km2, though scientists have suggested it was at least double that size during formation, with a current maximum thickness of roughly 12 km in the southeast. Several opinions and hypotheses about the nature of the subsidence that resulted in basin formation have been proposed: some consider it to have formed as a retro-arc foreland basin, while others have shown that geological and geophysical data do not support that theory. All have implications for the tempting shale gas formation within it.

By building the model of the southwest Karoo Basin, Scheiber-Enslin will be able to better approach these questions. She’ll be creating a 3D geological model of the Karoo Basin that will be used to investigate the tectonic environment of the Karoo, and the dynamic formation of the basin in terms of the flexural response on and off craton, and the possible formation of natural gas deposits.

It’s a real exercise in integration of diverse data sources. Her study is based on seismic and potential field data, and constrained using surface geological and structural information, magnetotelluric data, deep boreholes and Moho structure from teleseismic data; as well as magnetic depth-estimate methods to provide depth and boundary solutions.

Some of these sources are useful but are not high resolution. The Council for Geoscience of South Africa for example have collected and compiled gravity data since 1939, much of which is concentrated along roads with spacing stations of 14 km with barometric heights. However, “these Gravity data corrections have recently been reviewed and updated by the Council for Geoscience, improving the correction for atmospheric and height,” says Scheiber-Enslin.

In the 1970s, the Council for Geoscience began collecting and compiling aeromagnetic data too. The earliest surveys were flown using proton precession magnetometers, with a nominal 150 m flight height, 1 km flight line and 5 km tie line spacing. Mean aircraft speed was 240 km/h, resulting in a ~50-100 m along-line sample interval. In the 1980s, new Cesium-vapor magnetometers provided shorter cycle times and better along-line resolution.

“In addition, kilometres of seismic data collected in the region in the 1970s were recorded on paper reams and have passed hands over the years,” she says. “Thankfully, Falcon Oil had the data scanned and digitized.”

Scheiber-Enslin says the seismic and MT profiles she’s using are more recent: part of the Inkaba yeAfrica, Agulhas-Karoo Onshore-Offshore Geoscience Transect. The Agulhas-Karoo Transect consists of a ~600 km onland section across the Kaapvaal Craton, Karoo Basin, Cape Fold Belt and Kango Inlier, and a ~400 km offshore section over the southern continental margin of Africa. Onland datasets comprise ~240 km of wide-angle seismic refraction data, ~600 km of magnetotelluric data and ~100 km of Near Vertical Reflection (NVR) seismic data, all acquired between 2003 and 2006.

She explains that most studies of this nature use a basic uniform elastic plate to model flexure, but she wants to gain new insight into the possible evolution of the basin on and off the stable Kaapvaal craton. To understand how the mechanical strength of the continental lithosphere varies and how this affects the burial depths of sediments on and off the craton, she’s considering variations in rheologies and flexural responses to loading—important implications for shale gas formation.

As a step towards the model she has created a number of 2D potential field (gravity and magnetic) profiles using Geosoft GM-SYS. “Due to the regional nature of the gravity database being used and the non-uniqueness of potential field models, I used other data such as teleseismic, seismic and MT to constrain the model,” she explains. “Moho depth values and crustal structures for the model were derived from various published sources and imported into GM-SYS as background images for use while modelling horizons.”

She had hoped to use the Werner Deconvolution, Analytic Signal and Euler Deconvolution depth estimate built into Geosoft Oasis montaj to define the magnetic basement of the basin but found the basement is not significantly magnetic. “And there is the added complication of ~180 Ma Karoo basalt dykes and sills that have been emplaced at multiple levels throughout the Karoo basin,” she adds.

“These intrusions are magnetic and result in shallow signals that dominate the depth estimates, making deeper depth estimates difficult,” she says. So calculated depth estimates were loaded into the 2D GM-SYS models as symbols and compared with seismic and MT images. “Some correlation with seismic layers was possible,” she says. “The Geosoft tilt derivative was used to output solutions that were then used to run Fortran code that calculated the tilt depth from the magnetic data, again showing up a variety of depth including the basin and dolerite intrusions.”

While conducting research for the study, Scheiber-Enslin also established a need for updated potential field models to better constrain the source of the Beattie magnetic anomaly that crosses a large section of the southern part of South Africa from west to east. “I am currently trying to see how existing seismic and magnetotelluric data can be integrated with both magnetic and gravity data to test current theories as to the cause of this body, by including the body in my 2D profiles,” she says. So far she has found they correlate relatively well (on a kilometre scale) and provide a realistic geological model for the Beattie magnetic anomaly in the south of the study area, something that has not previously been attempted. “This model can now be used to constrain a source for the anomaly,” she says.

With success in the complex data integration process, she’s now gradually closing in on the tectonic model. “As part of the next stage, the two GM-SYS 2D profiles will be combined into a 3D model of the southwestern Karoo basin,” she says. “I have used the Geosoft regional and residual isostatic gravity calculations to help identify anomalous crustal or mantle bodies that will be included in the 3D model.”

She’s had her share of challenges. As well as the age of the gravity data, the older magnetic data isn’t of particularly high resolution. “It would be ideal to have higher resolution data to allow us to better image the numerous dolerite dykes and sills that intruded at multiple depths within the basin after the basin formed,” she says.

Another shortcoming has been the availability of consulting expertise. “There are a limited number of research geophysicists in South Africa whose brains we can pick,” says Scheiber-Enslin. “The majority of geophysicists move on to industry jobs.” Also, because exploration in South African has always been more mineral-focused, there are few geophysicists with experience in basin exploration. “Thankfully though, my supervisor in South Africa (Susan Webb) was already collaborating with Jörg Ebbing in Norway [thesis supervisor], who works in basin research at the Norwegian Geological Survey.”

She has plans to present the new model at a global geophysical conference. Doubtless there will be many exploration geophysicists and companies paying close attention.

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