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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...

A hybrid solution worth its salt

by Graham Chandler on March 26, 2015 technology

[Click to enlarge]

Voxel Assisted Layered Earth Modelling (VALEM) technology promises a significant advance in delineating the boundaries of subsalt structures. Shown above, a hybrid model generated with VALEM and GM-SYS 3D.

[Click to enlarge]

VALEM uses hybrid calculation techniques to do joint inversion on layers and voxels for more accurate representation of salt geometry and subsalt density distributions. Elements in a VALEM hybrid inversion model include grids, surfaces and voxels.

In many sedimentary basins around the world, ‘seeing through’ thick or steeply-dipping layers of salt is a major challenge for oil and gas exploration, especially in deep offshore environments. Seismic methods alone are usually insufficient to visualize the base of salt and the underlying sediments.

One thing is clear: Exploration success depends on knowing the location of the base of salt. Geophysical surveys help exploration teams evaluate the field, define prospects and determine drill targets. For example, if the geophysics indicates that the field extends farther updip due to the salt geometry, then more drilling may be needed or drill targets may be repositioned, whereas if the field is found to be more limited in the updip direction, a lot of unnecessary and costly deepwater wells can be avoided.

Delineating salt and sub-salt boundaries is a recalcitrant challenge for seismic interpreters. Additional data are often sought to supplement the seismic information, particularly in offshore and deepsea environments.

For years, researchers have worked at incorporating gravity with seismic data. “Since the beginning of modern subsalt petroleum exploration, geophysicists have tried using gravity data to help locate the base of salt in cases where seismic interpretations are uncertain,” says Gerry Connard, Senior Scientist, Potential Field Modeling, at Geosoft. “Typically the initial seismic interpretation is used to build a gravity model, which is adjusted to fit the gravity data and the parts of the seismic interpretation that have high confidence,” he says.

One integrated approach using wave-equation depth imaging and full tensor gradiometry inversion had some success in resolving the base of salt in an area where Kirchhoff depth imaging alone had failed. That attempt was carried out a decade ago at the K-2 Field in Green Canyon Block 562 in the Gulf of Mexico, some 180 miles south of New Orleans. However, as Connard notes, “the published results suggest that the gravity models required intensive manual intervention to accurately represent the seismic interpretations.”

A better modelling approach has eluded researchers. “Numerous exploration examples show that seismic data alone has difficulty mapping the base of salt,” says Rob Ellis, Principal Scientist, Earth Modelling, with Geosoft. “There is no established product for easily integrating gravity data with seismic data to map the base of salt.”

VALEM, (Voxel Assisted Layered Earth Modelling) technology was developed by Geosoft, in collaboration with potential field experts in the energy sector, to address this challenge.

“There have been a number of attempts to incorporate gravity with seismic,” Ellis says, but VALEM is “the first attempt to deliver this incorporation in a commercial, integrated, easy-to-use application specifically focused on the base of salt problem.”

A high-performance computing service for inversion modelling in the cloud, VALEM represents a significant advance in base of salt and subsalt imaging for energy exploration. Tightly integrated with Geosoft’s GM-SYS 3D modelling program, it results in an interactive solution for sub-salt interpretation that resolves the base of salt from gravity data bound by the constraints of seismic modelling.

Research on VALEM started in 2010, and it holds the best promise yet. A number of challenges remain, however; the chief one being how to integrate a seismic interpretation with a gravity one to provide an improved geologic interpretation. Or put another way, can gravity data supplement seismic data in determining the base of salt? “It’s possible that gravity data can help in some situations,” Ellis says, adding that VALEM’s unique approach to inversion modelling enables geophysicists to explore that possibility.

VALEM proposes a ‘hybrid inversion’ solution to the base-of-salt problem. Such an approach takes the best of layered-earth modeling and voxel-based inversion to allow for the full range of geometries associated with salt/subsalt structures. As Connard explains, VALEM advances the modelling technology in several ways. “VALEM models allow the use of three different types of data structures – layers, voxels, and 3D triangulated surfaces – within a single model. Modelers can use the most appropriate representation for each model element and quickly build complicated models.”

VALEM also uses hybrid calculations by combining both frequency-domain and space-domain calculations where appropriate. Says Connard: “Because space-domain calculations are computationally expensive, VALEM performs the space-domain calculations using server clusters in the cloud, providing high-performance computing for the desktop.”

Connard and Ellis, together with Geosoft researchers Tom Popowski and Gaud Pouliquen, recently did some theoretical testing of VALEM. Their findings were presented at a 2014 workshop organized by the Society of Exploration Geophysicists (SEG) and the Chinese Geophysical Society in Chengdu, China; and more recently at Finding Petroleum’s Non-Seismic Geophysics event held in February.

MORE: Finding Petroleum presentation on 3D Hybrid Gravity Inversion for Base of Salt Modelling

For the presentation, entitled Hybrid strategies for modelling gravity gradient data, the research team used SEAM I Earth model data and hybrid modelling. SEAM (the SEG Advanced Modeling Program) is a partnership between industry and SEG which aims to advance geophysical science and technology through the construction of subsurface models and the generation of synthetic data sets. The SEAM I model used by the Geosoft researchers describes complex salt structures comparable to those found in the Gulf of Mexico. The researchers performed a seismically constrained inversion of Falcon airborne gravity gradient data to map the base of salt in the SEAM model. The results demonstrate the capabilities and potential of VALEM.

“The exercise points to the progress achieved in VALEM while demonstrating some of the challenges that remain,” Connard says. The main challenge in combining voxel and layered models in a hybrid inversion is that voxel inversions generally produce models which have ‘smoothed’ transitions between domains whereas layered earth models have discrete transitions. “To overcome this inconsistency, we developed a voxel method which effectively produces either a target domain (salt) or a host domain (sediments) with sharp transition,” he says. “This is the key to hybrid modelling.”

For optimal results, the use of VALEM in the base of salt scenario requires an interpreted, depth-converted, 3D seismic survey plus a gravity or gravity gradient survey covering the area of interest. Regional models of the surrounding area will help improve the results. The better the quality of the data, the better the outcomes.

Since December 2014, three exploration and production companies and one consultant have been involved in testing VALEM with real project data from salt basins around the world.

These tests are proving out the application of the hybrid inversion approach in a realistic environment, says S. Bruce Kohrn, Energy Segment Lead at Geosoft. “VALEM is the result of five years of research and development, and the application is now ready for release,” he says, adding that he anticipates full commercial roll-out by mid-2015.

Longer term, VALEM applications likely won’t be restricted to base of salt determinations. Other potential applications include basin analysis and sub-basalt imaging to support subsurface investigations. “In fact,” says Ellis, “there is potential to apply VALEM inversion modelling in any situation where a discrete contrast is required and there is a mixture of surfaces/layers and compact bodies.”


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