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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...

Narrowing the Field

Advances in processing and interpreting gravity and magnetic survey data are opening up highly promising new roles for the technique in oil and gas exploration.

By Graham Chandler

For those explorers who hunt for oil and gas, there was a time when gravity and magnetic surveys were considered the coarser, rougher first cut to zero in on the best locations to set up their seismic gear. That’s all changing now. Increasingly, gravity and magnetic (grav/mag) methods are being used to complement and constrain traditional seismic data or even used as the only tool.

Wintermoon Geotechnologies of Denver, Colorado is a consultancy that has specialized in the grav/mag field, using these geophysical techniques and blending them with seismic to achieve greater success in oil and gas exploration. What’s behind this success? “Gravity and magnetic data quality has improved significantly since the 1980s,” says Dr. Michal Ruder, Wintermoon’s president. “Not only can we acquire data more quickly now, but also our data resolution is much better and we can now resolve more subtle (lower amplitude and shorter spatial wavelength or high frequency) perturbations in both the gravity and the crustal magnetic fields. This improved resolution now allows us to imagine very small-scale and shallow lateral variations in density and magnetic susceptibility.” She says these are often associated with the hydrocarbon play itself. “Modern gravity and magnetic surveys can now provide a set of observations that is more directly associated with hydrocarbon play character, in addition to the ‘traditional’ regional information for which we have long used potential field data,” she says.

Previously difficult geologic settings can now be explored in detail using gravity and magnetic methods for situations where traditional seismic alone has been less successful. Ruder explains why. “Seismic data quality is not uniform in all geologic settings,” she says. “Due to their elastic properties, some rock lithologies do not readily transmit acoustic energy. As a result, seismic signals can be greatly attenuated, providing little or no seismic imaging below these acoustically-challenging horizons.” Where there is a significant lateral density variation below the problematic acoustic horizon, she says gravity can provide unique information about these rocks, primarily because gravity is not negatively impacted by rock elastic properties. In general, independent geophysical techniques linked to the same lithological model will respond to different geophysical properties, like density, susceptibility or resistivity, so their integration can be valuable.

A common imaging problem for seismic operators where grav/mag can enhance the geologic picture is where there is a near-vertical fault or interface (like a salt or shale diaper). “Seismic signal is typically scattered by these interfaces,” says Ruder. “In contrast, both gravity and magnetics have their best imaging at vertical interfaces across which lateral density or magnetic susceptibility contrasts exist.”

In fact, for oil and gas explorers, some geologic situations almost demand that gravity and magnetic methods be used; where they can become an indispensable boost to seismic explorations. Reducing the uncertainty in interpretation of complex sub-salt reservoirs is a case in point. Ruder has had considerable success using the approach in the salt-prone basins offshore West Africa, South America, North America and northern Europe. “Gravity methods are vital for providing an independent corroboration of total volume and shape of salt when investigating sub-salt hydrocarbon potential,” she says. “Seismic data quality can be significantly improved when we use gravity modeling results to improve and refine our seismic velocity model of the base of salt. This result is fed back into the seismic pre-stack depth migration processing to provide an improved seismic image of the sub-salt horizons’ geometries.” She adds that this ultimately leads to more successful prospecting.

Indeed when it comes to subsalt interpretations, advancements in and integration of techniques have been largely responsible for the massive deep offshore hydrocarbon discoveries of the past decade. Examples from several regions show where multi-disciplinary 3D modeling helped to delineate allochthonous salt distributions. In many cases, e.g. where the base of salt could not be clearly identified from seismic data, the integrated approach revealed its geometry and salt thickness, a major step for better imaging of target structures below salt.

As many as five or six different techniques can be integrated to optimize salt geometry interpretations. Savvy operators have reported successes for example in the Gulf of Mexico applying combinations of 3D gravity, full tensor gradient, magnetic modeling and inversion, using such constraining data sources as seismic, magnetotellurics, gravity and borehole data. Qualitative and quantitative interpretations have provided good control of salt location and volume. Moreover, interpretation of high-resolution gravity and seismic depth imaging has produced significant increases in resolution of complex geometry images of salt structures. The significant savings gained in cost and time are proving invaluable—as well as the vastly improved odds of accurately identifying geological targets.
But seismic techniques remain indispensable: precious few oil and gas discoveries are made without the use of seismic methods. However, other geophysical methods can assist with more reliable evaluations in these deeper, more challenging environments. Gravity and magnetics will never trump seismic completely; nor entirely replace it—they’ll continue to be complementary tools. “Gravity is correctly characterized as a ‘low-resolution’ geophysical exploration tool,” says Ruder. By cost-effectively gathering geophysical data to narrow the search area within large fields, oil and gas explorers can refine their targets and apply seismic techniques more productively. “Without constraining information, a gravity model can be modified in an infinite number of ways in order to match the observed gravity signal. Seismic, well log, and other geologic data provide critical constraining information for gravity models, limiting the degrees of freedom of our modifications and enabling us to produce a meaningful, constrained earth model that is consistent with both gravity and seismic datasets.”

It makes interpretation more rewarding but not without new challenges. Ruder uses a multi-faceted approach to interpretation. “We work hard to identify and separate ‘regional’ and ‘residual’ signals within the observed gravity and magnetic datasets using our state-of-the-art Fourier-based 2D filtering routines,” she explains. “We construct models which incorporate geometries and physical properties derived from all available geologic and geophysical data, and we then invert the observed gravity and magnetic data to gain further insight into the geologic question at hand.” She says she’s used the approach successfully in prospect evaluations in the Gulf of Mexico, and offshore Brazil and West Africa.

None of this could be accomplished without a good suite of software. Most geosciences consultants prefer to work in multiple software environments dictated by individual project needs or client preferences. Ruder employs a full and diverse set—for data entry, data processing, data enhancement and quantitative modeling; so a seamless interface is one critical consideration. She says using Geosoft as a major part of her software suite makes this easier, for example it has the ability to ensure compatibility with ArcGIS, which she and others use extensively. It allows direct import of her grav/mag data for constraining the seismic. Ruder likes the fact that it goes both ways. “I can take my Geosoft products and move them into the ArcGIS world or open up an ArcGIS map project in Geosoft.”

As the use of gravity and magnetics in oil and gas exploration advances, it can even tell itself whether it will work or not. To see if gravity and magnetics will help answer her client’s geologic question, Ruder often uses Geosoft GM-SYS. Somewhat ironically, it is gravity and magnetics themselves that tell her the feasibility. “It can be used in two important phases of our projects,” she says. “The first is as a sensitivity model. There are certain geological settings where gravity and magnetics won’t work. Using GM-SYS to construct a theoretical model to test that sensitivity of the tool in a particular geologic setting will help us determine whether it’s even worthwhile to do a gravity and magnetics acquisition of data. That means we are asking a question that gravity and magnetics can answer, that is, can we go ahead and do the project?  Assuming our results of the sensitivity testing indicate that grav/mag will provide the required insight and the project moves forward, we then use GM-SYS to build our constrained earth model of the survey data.”