The people, science and technology behind discovery

Subscribe to the Magazine

Get new articles sent directly to
your mailbox.


Join the network

Twitter Updates Group Forum

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...

New Technique Reduces Risk for Offshore
Oil Explorers

California-based eField Exploration LLP goes to the Norwegian Sea and completes first offshore survey using its new-generation airborne Electro-Magnetotelluric technology

By Graham Chandler

Electro-Magnetotelluric (EMT) doesn't easily roll off the tongue and it's not exactly a household word but that doesn't detract from the technique's exciting possibilities when it comes to looking for oil and gas from the air.

After proving their EMT technology with five successful airborne surveys over shale gas properties in Texas, culminating in mapping the complex Rhombochasm field at a depth of 10,200 feet flying over the Palo Duro Basin of Cottle County, eField Exploration LLP of Yorba Linda, California, decided to broaden the concept to offshore surveys. "The minute you say offshore, that opens up the whole world," says Ed Johnson, president.

Their first overseas stop was Norway. Contracted by a Norwegian JV, eField undertook an airborne survey in the Nordland area of the Norwegian Sea with the objective of rapidly assessing the potential of multiple blocks for the Norwegian Petroleum Directorate's 20th Licensing Round in 2008.

"Rapid" was the operative word here. Flying 100 miles offshore over water up to 1000 feet deep, the data acquisition was completed in less than a week with the company's specially-designed sensor package. Johnson says conventional methods such as marine seismic would have taken months at several times the cost. "Our offshore Airborne System can cover up to 500 line miles per day at a fraction of the cost of a marine survey," he says.

Several airborne methods utilize measurement of electric and magnetic fields for resource exploration but the key difference with eField's EMT is the use of the natural electrical flows though the earth called telluric currents. These are induced by natural electric phenomena such as energy from solar flares and lightning strikes that penetrate deeply into the earth. As they travel beneath the surface, telluric currents become distorted by different types of rock and subterranean structures. By recording and processing these signals, the nature of these underground features and compositions can be deduced.

It's a passive system; using natural EM fields as the energy source rather than transmitting a high-energy EM signal. Measurements include electrical resistivity and conductivity, interfacial polarization, dielectric properties and magnetization. Normalized components of E and H are measured to obtain Natural Field Apparent Resistivity, or NFAR, and conductivities down to 30,000 feet and more.

Because of their depth, detection and interpretation of their behaviour can be used to look much further below the surface than traditional methods—up to seven kilometres or more. They become useful in the search for oil and gas because these deposits are natural insulators with high resistivity compared to water. Such differentiation allows modeling and identifying anomalies which can be attributable to the structures that potentially could host hydrocarbons.

Oil and gas reservoirs are generally a combination of brackish water and dissolved hydrocarbons. When telluric currents flow through the boundaries between hydrocarbons and water, they develop strong interfacial double layer electric charge effects. The accumulation of these charges results in an anomaly seen from the air by the eField Airborne EMT System. It's a phenomenon known as Natural Field Induced Polarization, or NFIP.

While the use of ground electric and magnetotelluric surveys have long been important oil and gas exploration tools, no one had applied the science in an airborne system focusing on these natural electric fields before. "We were the first for oil and gas, in 2002," says Johnson.

Conceptually, detection is relatively simple. Using a typical survey aircraft such as a Piper Navajo, Cessna 320 or KingAir, the patented system detects telluric flows by way of electric field sensors mounted in wingtip pods. The sensors include three orthogonal dipoles oriented along the X, Y and Z axes, and are attached to angular motion sensors that compensate for the angular motion of the airplane in strong fields. A total field magnetometer mounted in an eight-foot long tail stinger provides phase and amplitude references for the electric field sensors that enable them to provide accurate flow information about the telluric currents.

Not only location, but the source and composition of the hydrocarbon reservoirs are determined using the Airborne Offshore System. It maps the electric charge effects associated with dissolved hydrocarbons—microseeps—as they migrate to the ocean's surface, exploiting the fact that the hydrocarbons transform to aerosols at the surface. In moving from a highly conductive environment (seawater) to a highly resistive environment (air) they generate two distinct and measurable anomalies.

To further map these hydrocarbon seepages, eField sources information from the ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) satellite sensor from a strategic partner. It's a useful and proven data source as scientists have demonstrated good correlation between spectral anomalies observed on ASTER data and known production.

Utilizing all these sources the partner has developed a general seepage model. Johnson explains that the imagery is processed using their Sea Enhancement Algorithm, then enlarged and printed for seep detection analysis and interpretation. "They employ a rigorous ranking system that assigns a value ranging from 1 to 10 to convey the analyst's level of confidence that a detected sea surface anomaly actually represents and oil slick caused by natural seepage, rather than some other source," he says. The ranking considers image data, typical anomaly characteristics, geologic and cultural setting, illumination parameters, and several other factors that may affect seep detection and discrimination.

The data reside on the company's custom database which interfaces with Geosoft's Oasis montaj software. That allows the integration of several other earth science datasets and images, including 2D and 3D seismic, satellite imagery and surface geochemistry. "The Geosoft platform has been very easy to adopt and apply to our incoming data stream needs," says Johnson. "Flying the first passive EM system for oil and gas means that the existing minerals based architecture didn't suit our sensor outputs. But we were easily able to build back-end databases to accept incoming sensor information (14), create automatic QC routines, and then build front-end tools for data analysis." He says the tools can almost run in real time and permit analysts to spot potential data for detailed interpretation.

"With the total package," Johnson says, "eField's technology enables airborne exploration of up to 100 square miles a day, detecting the presence of hydrocarbons to depths of well over 20,000 feet."

"The projected savings in cost and time, as well as the elimination of environmental damage caused by conventional surveying, will potentially enable the oil and gas industry to enter a new phase of exploration that has thus far been cost prohibitive," he says.

Moreover, there's the element of ease of access. "Early adopters are using airborne EMT where seismic is difficult or where access is a problem," says Johnson. "Or where additional data will help to high-grade many prospects (de-risking)." It doesn't replace seismic, however. "At this stage in development we are an adjunct to seismic or can plan where seismic would be more beneficial," he explains. "The known presence of hydrocarbons permits us to refine our interpretation using analogues."

It's a promising start as the company refines its offshore method. "It is developmental," says Johnson. "We are cataloguing responses in different settings so we are still discovering the full potential. Offshore Norway proved that there is a whole new world of potential available."

Many clients come to eField after having difficulty using traditional methods. "You know you are brand new from a technology standpoint when you tend to get used where other things don't work," says Johnson. "People will try new technology. Where seismic effectively doesn't work in these [Texas] shale formations for example, they've been trying other methods." And it's not only oil and gas, he adds. "It's the same in northern Saskatchewan where there's a lot of overburden—we're being looked at to fly for uranium because the existing systems don't go deep enough," he says, "and yet the passive systems like magnetics and gravity don't do the job. So there are applications where we can enter the market maybe because nothing else works." The only drawback to keeping busy in learning new applications he says is "it means extra time to figure out what we're seeing."

For eField's future, "data modeling is the next step as well as quantifying the results," says Johnson. "Integrating the results with existing oil and gas industry IT platforms is our immediate next priority."