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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...

Giving seismic an uplift with gravity and magnetics

Taking the time to integrate gravity and magnetics with seismic data can pay off for oil and gas explorers with limited budgets

by Graham Chandler and Carmela Burns on June 16, 2015 expertise

Bridgeporth aircraft surveying in Africa, with surveying equipment in the foreground.

For oil and gas explorers who want to maximize targeting effectiveness and minimize costs, Jonathan Watson has a message: Gravity and magnetics interpretation is a low-cost exploration technique that can add a lot of upfront value to your exploration program.

“It’s expensive to go in with just seismic first,” says Watson, who is interpretation manager at Bridgeporth Ltd, a geosciences company in Milton Keynes, U.K. “Using gravity and magnetics at the outset can often help you understand what’s going on with minimal costs, and it allows you to fine-tune and improve your seismic program based on what you’ve learned.”

A specialist in the integration of gravity and magnetics with seismic data, Watson shares some of his views in a webinar titled “Integrating Potential Field Data with Seismic Data and Structural Geology”, based on his presentation at last year’s conference of the European Association of Geoscientists and Engineers, held in Amsterdam.

Gravity and magnetic, or potential field data, methods have been around for some time but continue to be underused in oil and gas exploration. According to Watson, this is partly because explorers are generally under pressure to produce seismic results ahead of funding deadlines. Moreover, if potential field companies generate only geophysical models when the oil company geologist needs geological models then a disconnect can occur.

Another challenge is lack of experience with potential field data methods. “When a gravity and magnetic dataset has been interpreted outside of the oil companyby an independent expert and delivered as a package,” explains Watson, “some clients will take a look at it and not fully understand what they are looking at. It could be a perfectly good piece of work that tells them a lot, but it’s put aside because it’s not well understood.”

Knowing how to use gravity and magnetics, and at what stage in your exploration program, is key to optimizing its value. “In a frontier area, for example,” says Watson, “gravity and magnetics are the first datasets, or one of the first, that are acquired. At this stage, they can reveal a lot about basins and other geological features, which in turn can help define the seismic program.”
“This approach can be especially useful in frontier areas such as Africa. Broad areas can be covered, by acquiringlarge datasets quickly and cheaply from the air with minimal time spent on the ground,” says Watson. “That can be important from both security and environmental viewpoints.”

While there is an obvious advantage in frontier exploration, there are many other cases where integrating non-seismic data with the seismic makes sense explains Watson. “Interpreters can use gravity and magnetics to investigate problems or anomalies found in the seismic in areas already explored,” says Watson, “or marine environments where potential field data have been acquired alongside the seismic and explorers don’t have the luxury of examining it prior to seismic acquisition.”

Where oil and gas explorers do use potential field data, gravity is the more popular, he adds. “It can show a number of different geological features, be it faulting, anticlines/synclines, intrusives, basement blocks, salt domes etc.” But magnetic data are also highly relevant. They can indicate depth to sources, basement structure, and the lateral extent of volcanics, especially where there are shallow intrusions. Magnetic data are often recorded alongside gravity and so are frequently available to integrate.

Some explorers shy away from magnetic modeling, because they are not familiar with it.

“Magnetic modeling is generally more challenging than gravity modeling,” Watson observes. “Gravity is definitely easier to interpret in that if you have a gravity high, you are looking at a denser body whereas with magnetics, because of inclination, declination and remanence [residual magnetism] is not as easy to interpret.”

Still, one can learn and it’s worth the time invested. Watson cites “Aeromagnetic Surveys – Principles, Practice & Interpretation, an eBook by Alan Reeves, as a good starting point for learning how to acquire, process and interpret magnetic data. It is available free online.

When it comes to gravity-derived structural mapping, Watson recommends having the first pass interpretation done automatically. “Automatic mapping is useful as it can be completed quickly, especially over a large, detailed area and supplied as an initial interpretation.” A manual interpretation follow-up, with classification and more constraints, can then add to the interpreter’s knowledge, resulting in a more complete structural map.

Such a process can help gravity’s differentiation between basement rocks and highly compact sediments, provided there is sufficient density contrast. Density contrast is key. “Salt domes are, with the correct acquisition parameters, usually well-imaged by gravity data, as a large density contrast can exist,” says Watson. “Gravity data are extensively used in areas of salt due to the likely low-density contrast with surrounding sediments.” Offshore areas where this process has proved successful include Brazil, West Africa, the North Sea; onshore areas include Gabon, US and Poland.

Integration of other data types can help complete the picture; a good example being geochemical data. Watson says although it is often not available for frontier areas, surface geochemical data can indicate a working petroleum system, though it usually reveals little about its size or extent. “Geochemical and other data can give you an indication of vegetation, for example, and the composition of the soil,” he notes, “and there are ways of using that to indicate the possibility of oil and gas. But what those techniques can’t tell you is what’s happening deep under the ground.”

Integration of additional potential field techniques such as MT (magnetotellurics) can be considered, along with well-logging data. Generally, the greater the integration with other datasets the better, says Watson, conceding that the limiting factors are always time management and cost. “You can’t always turn things into an academic project, much as you might want to.”

Time and cost aside, for the best overall results, integration of the datasets is key. “A combination of potential field data, seismic and geochemical can produce an integrated model,” says Watson, and in frontier areas, that can be crucial. “The establishment of a working system is key for companies to assist with exploration funding, farm-ins, et cetera,” he explains in the web-based seminar. “It builds a strong case for a potential exploration target.”

[Click to enlarge]

Example of data processing displayed within Geosoft

[Click to enlarge]

Processed gravity data displayed within Geosoft’s 3D Viewer.

Watson’s technology toolkit includes Geosoft, which offers several packages that are useful for creating integrated interpretation. “GM-SYS software has tools for 2D and 3D gravity modelling and the ability to integrate with seismic and well data to produce depth surfaces that are key to seismic interpretation,” says Watson. “It allows you to bring the seismic in and effectively visualize the gravity and seismic data within the same software. Therefore, you can use it to create a model to satisfy both datasets. GM-SYS runs on top of Oasis montaj, which is the core platform for processing and working with gravity and magnetic data before integrating them with the seismic.”

Joint inversions can also be effective, adds Watson. “Regardless of whether it is a true joint inversion or simply the results of each dataset combined to produce a balanced result, as long as the final model is constrained by all the available data, then it is an improved model. Programs such as the recently introduced VALEM (Voxel Assisted Layered Earth Modelling) could result in even more improvements. Anything that allows more than one dataset to be used is good.”

Going forward, Watson sees more potential for gravity and magnetics in the seismic arena. “There is quite a lot of R&D going on – for example, techniques that are being used in the mining industry but haven’t crossed into oil and gas.” These include different ways of acquiring and integrating data. In shale gas exploration, there are ways gravity and magnetics could assist with mapping of natural fractures—areas of weakness or areas where fracking is going to be the most successful.

With today’s focus on using integrated geophysical methods to deepen insight and achieve greater precision in targeting, it’s safe to say use of potential field data will continue to increase – and the value is being proven in the field. To fully unlock this value, Watson sees the need for broader understanding of how and when to use potential field data methods in the exploration process; and efficient workflows and software that allow integration without delaying the exploration program.

 “At the end of the day,” he concludes, “gravity and magnetics can add significant uplift when integrated with seismic – and it’s something you can easily fit it into your exploration program, with the right know-how, planning and software.”

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