by Lesley Stokes:
by Lesley Stokes:
The paper from Geotech Ltd. has been awarded as the Best Paper in the Mining and Geothermal sessions at the 2015 SEG annual meeting in New Orleans: “Airborne Inductively Induced Polarization effects in and their removal from the VTEM data from Mirny, Russia”.
As the Committee Chair says: “Out of all the papers presented, it was voted as highest ranking by the session participants”.
The paper is about airborne inductively induced polarization (AIIPTM) effects, which is expressed in the form of numerous negative transients, and observed in the VTEM helicopter time-domain EM (TDEM) data from Mirny, Russia. VTEM data reflect mainly two physical phenomena in the earth: i) electromagnetic induction and ii) airborne inductively induced polarization (AIIP) related to the relaxation of polarized charges in the ground. Typical AIIP effects in the VTEM data from Mirny corrupt only the early to mid-time channels, from 55 microsec to 400 microsec. Moreover, the earliest few time channels, from 18 microsec to 48 microsec, are not affected by AIIP, because the IP effect takes a finite time to build up. Cole-Cole analysis of the AIIP affected VTEM data showed that the frequency factor and the time constant are close to 0.8 and 0.0001s, respectively. Since the earliest time channel data are not affected by AIIP, the resistivity of the shallow ground can still be precisely determined. As a result, the purely inductive VTEM decay can be accurately modelled and used to remove the AIIP effect from later time-channels.
by Gemma Barson, Oct.30, 2015
A new study by the U.S. Geological Survey and university researchers that was published earlier this year has discovered that of the 94,870 people living in tsunami hazard zones in northern California, Oregon and Washington state, about 21,500 would not have time to reach higher ground were a tsunami to hit their community.
For many communities and local authorities this has led to an increase in demand for vertical evacuation structures that would enable residents to evacuate safely without having to seek higher ground (perhaps in the form of a beam type structure, or the fortification of an existing high building). However, more important issues thrown up by this study are that the existing infrastructure within these communities are so old and potentially structurally unsound that, were a tsumani to hit, bridges would crumble and dams would fail, blocking the potential escape routes of tens of thousands of individuals and leading to significant loss of life.
This leads to a huge assignment for geophysicists who have been tasked with utilizing innovative new technologies that have developed in the field of passive seismic to image the subsurface and the incredible details that these can pick up in a non-intrusive way. Whilst it was first adopted (and still has very lucrative applications for) the sourcing of underground oil wells and other vital resources, passive seismic near-surface geophysics can also be applied in other incredibly useful ways. It can be used to ascertain the ways in which passive sources (such as nearby train stations or large car movement on a highway) can impact both on earth movements and the surface of the earth’s structure, as well as ascertaining the impact that these have, particularly on aging infrastructure such as these bridges, dams and levees. It is clear that near-surface applications are both increasing in number, and that their societal value only continues to rise.
The Practical Considerations
The practical considerations that surround the field of passive seismic research are huge. Practitioners can choose to either temporary arrays deployment or, if they want to permanently monitor the seismic changes in a particular location, they can choose permanently installed sensors: there are, of course, pros and cons associated with adopting both systems. The largest technical risk is the sensitivity of the system, and how it will be negatively affected by any external noise and change, whilst financial implications are also a huge concern. Because passive seismic imaging is a quickly growing technology, it can also be very expensive to undertake. The purchasing and maintenance costs of the equipment is huge, particularly when the costs of the vehicular support that is needed to transport the equipment and access remote monitoring locations, as well as the costs of insuring and protecting all of that equipment are taken into consideration. These costs could vary considerably depending on where you are based, and where you choose to purchase your equipment, with technological hardware and software, and any related insurances, generally being considerably more expensive in Europe (particularly in the UK) than in North America.
The Society for Exploration Geophysicists have recently announced their new president as John Bradford: a specialist in the field of passive seismic research and very vocal about the potential wider implications that the new technologies surrounding the field can have. It seems that under Bradford’s leadership, focus throughout the society will shift to focus on passive seismic research, to the benefit of those working within the field. Monitoring failure cases are likely to be minimized as the technology involved in the process develops, and this will only make it easier to ensure that the vital infrastructures on which all of our communities depend can be maintained and updates as necessary.
Climate change is happening, and more and more communities are under threat from tsunamis, increased earthquakes, and other natural disasters. By deploying passive seismic monitoring to help us best understand how to strengthen our infrastructure and ensure that our bridges, dams, and other vital services can be rebuilt or repaired in such a way that will minimize the impact of these natural disasters, we can use passive seismic systems for the benefit of our greater communities.
Canadian Journal of Earth Sciences has published an article “Fault reconstructions using aeromagnetic data in the Great Bear magmatic zone, Northwest Territories, Canada” written by Nathan Hayward, Louise Corriveau from Geoligical Survey of Canada.
The authors have chosen for the investigation the Great Bear magmatic zone (interpreted as a Paleoproterozoic magmatic arc) which includes economically important mineralization of vein-type silver, radium, and uranium deposits, polymetallic iron oxide copper–gold and iron oxide ± apatite.
Geological development of the Great Bear magmatic zone is described in details in the paper including magmatism, tectonic (folding and faulting) events. A model of conjugate transcurrent faulting with the principal shortening direction and the boundary of the system has been presented.
The aeromagnetic data used for the study has been compiled and integrated from different sources including public archival aeromagnetic data and data from private sector. In the result of the integration, nearly complete high-resolution coverage of the Great Bear magmatic zone was obtained.
The magnetic data interpretation process included regional magnetic interpretation and detection of magnetic lineaments related to faults and dykes.
In the result of this work authors made structural reconstruction of the Great Bear magmatic zone, analysed horizontal offsets on fault zones and developed Vertical Offset Rotation Model and Maximum Offset Model. In the conclusion the authors made an analysis of mineralization distribution in connection with the structural units.
The full paper with tables and all pictures is here..
by Alexander Prikhodko
During the last few years the topic about IP effect (induced polarization) in the EM (electromagnetic) transient method (mostly in airborne time-domain) has been actively raised by many authors through geophysical magazines, conferences and meetings.
Here we will look into the topic without formulas and deep theory for a better understanding of the IP effect by general users of electro-prospecting methods.
The nature of the IP phenomenon is universal regardless of an electric field source inducing (causing) the phenomenon or a measurement way of the appearance. First of all, the IP theory is out of Maxwell equations solutions because the process is accompanied by mass transfer and connected with EM field transformations. In contrast to IP theory Maxwell’s equations deal with electromagnetic induction which the time-domain (transient) method is built from.
In the case of IP the term “induced” means “caused” and does not relate to the concept of EM induction.
The concept of Induced Polarization (a substance ability to separate opposite charges) incorporates different phenomenons but related processes that occur:
1) in heterogeneous fluids or in pores filled with fluids;
2) due to electrochemical processes.
These two phenomenons – electrokinetic (1) and electrochemical (2), is a key to understanding how IP is used in applied geophysics.
Electrokinetic processes occur on contacts between ionic conductive fluids and a solid phase.
Electrochemical processes occur on contacts, or surfaces, between phases with electronic (metallic) and ionic (non-metallic) conduction. This is fundamental when IP method used when exploring for sulfide mineralization, especially if the sulfides are disseminated as the IP effect will be stronger than for massive sulfides of the same volume because its surface area is less.
Historically electrochemical nature of IP phenomenon first investigated and used in geophysics by Conrad Schlumberger (published in 1920). Later, during further electronic industry development and equipment sensitivity and bandwidth increasing, IP effect began to be observed all over the geologic environment due to the possibility of measurement of rapid and comparatively weak IP signal of the electrokinetic nature.
Generally, the IP effect of both natures potentially may affect data obtained with any electro-prospecting method including inductive time-domain method, regardless that the strongest IP effect occurs in the geologic environment at galvanic (grounded) way of the current inducing and the voltage measuring.
So, the IP component in transient or time-domain data is a parasitic effect which is not under Maxwell’s EM theory. (By the way, in the widely employed original DC-IP method, the inductive component is considered as a source of noise.) There are some technical requirements to sensitivity, bandwidth and geometry of a time-domain system to get better the parasitic signal superimposed on the inductive, native to the method, component.
Fortunately the IP parasitic signal is opposite to the inductive secondary field component allowing to recognize it and separate out it in some cases from the measured total secondary field. The favorable condition to get IP component from time-domain data and investigate it is rapid decaying inductive secondary field, i.e. resistive environment in general is favorable, but there are cases when a strong IP component is prominent in presence of long inductive decay.
Unfortunately the existing theories of the electrokinetic and electrochemical natures of the IP phenomenon are on a qualitative basis. It means there is no chance to get petrophysical or/and petrochemical parameters of the geologic environment and to classify the IP sources according to their nature. On practice, empirical approximations are used for the IP process description with limited controlled parameters (in particular, Cole-Cole formula and the corresponded parameters) despite the nature of the phenomenon. To our delight it enables creative and thoughtful geological interpretation of the IP data if we get it correctly.
by VIRGINIA HEFFERNAN on MARCH 30, 2015
The founders of Insight Geophysics have deep roots in the past, but their approach to Induced Polarization (IP) represents the future of mineral exploration: real time interpretation of data, integration of non-geophysical information with 3D inversions, and a dynamic style of surveying that allows for tweaks on a day to day basis depending on feedback from the exploration team.
– See more
Geophysics Lectures in University of South Alabama:
Introduction to Geophysics; Seismic Stratigraphy; Wave Theory Refraction and Reflection; Petroleum Generation and Migration; The porosity Logs; Gamma ray logs; Electric SP and Resistivity Logs and many other are on KHURRAM TANVIR Official Page
During mineral exploration programs using geophysical methods it is highly important to know exploration models and mineralization controlling factors for proper choice of geophysical interpretation methods and approaches.
Clive Willman, geologist and film-maker, has created a series of short films covering Orogenic Gold Deposits, their formation, fluids and faults, illustrating with examples such as the Morning Star and Stawell Gold Mines in Victoria (Australia); The Metamorphic Gold Model; Gold, Faults and Fluids.
Clive presents his subject by way of interviews with leading workers in the field. Clive has worked as a geologist in both Industry and for the Geological Survey of Victoria, and brings a degree of authority to his film-making in this discipline.
P Kovesi, E-J Holden and J Wong
ASEG Extended Abstracts 2013(1) 1 – 5
The ability to integrate data from a range of different images is often a crucial requirement for successful interpretation. Interactive multi-image blending is presented as a tool for facilitating the interpretation of complex information from multiple data sources. Traditionally, image blending has only been considered for cross-dissolving effects between two images. However, it is common for there to be more than just two images of interest in an interpretation task. We have developed a family of different multi-image blending tools to fill this need. These have been designed to support a number of different interpretation tasks and image types. For image blending to be a useful tool for multiple image interpretation it is important that the association between features and individual input images remain identifiable and distinct within the blend. We argue that interactivity of the blend is an important component for achieving this. Blending can also be usefully employed to interactively explore parameter variations for enhancement techniques. Often the best parameter values to use cannot be known beforehand, and it is common for different regions of an image to require different parameter values for best enhancement. By preparing a set of images processed over a sequence of scales and parameter values, and then interactively blending between these images, the interpretation of a data set can be greatly facilitated.
A team of researchers at The University of Western Australia has been recognised for its work to develop the most innovative use of a geophysical technique.
Research Professor Peter Kovesi, Associate Professor Eun-Jung Holden and Assistant Professor Jason Wong, won the Laric Hawkins Memorial Innovation Award at the International Geophysics Conference and Exhibition 2013 in Melbourne for their paper “Interactive multi-image blending for data visualisation and interpretation”.
The award is given for the most innovative use of a geophysical technique from a paper presented at the conference. The paper was delivered by Peter Kovesi.
Geoscientific data interpretation aims to understand complex geology in Earth’s subsurface by using a range of information including different types of geophysical, geological and geochemical data.
The ability to integrate a range of different sets of data is often a crucial requirement for successful interpretation, but this is a challenging task which often results in interpretations that are subjective and unreliable.
Nevertheless, these interpretations form the basis of significant economic, social and environmental decisions by resource industry and government agencies.
by VIRGINIA HEFFERNAN on DECEMBER 11, 2013 EXPERTISE
“Despite a steep appreciation in exploration spending over the past decade, the number of greenfield discoveries is falling every year. Narrowing this gap will require harnessing the power of big data and cloud computing, according to a presentation by Rio Tinto’s exploration chief Stephen McIntosh at the International Geophysical Conference in Melbourne.
“In a lot of cases, we have the data but we haven’t got the most out of it because of time constraints and our ability to find or “discover” this data,” Amanda Butt, McIntosh’s colleague and former manager of exploration and geophysics, said in a follow-up interview with Earth Explorer. “Now that we can do things more quickly, and efficiently we can get more effective information out of the data.”
Geophysics, in particular, has become an increasingly important exploration tool as the depth of the average discovery moves from close to surface in the 1950s to hundreds of metres deep. Indeed, geophysics contributed significantly to nine of the 16 greenfields discoveries Rio Tinto has made since 1996, including the Diavik diamond mine in Canada and more recently at the La Granja copper project in Peru.”
IAEA (International Atomic Energy Agency) has published a book “Advances in Airborne and Ground Geophysical Methods for Uranium Exploration”.
“Due to growing global energy demand, many countries have seen a rise in uranium exploration activities in the past few years, and newly designed geophysical instruments and their application in uranium exploration are contributing to an increased probability of successful discoveries. This publication highlights advances in airborne and ground geophysical techniques and methods for uranium exploration, succinctly describing modern geophysical methods and demonstrating their application with examples.”
MARCH 8, 2013 EXPERTISE
Matching an exploration target with a geophysical technique can be tricky for an explorer, partly because there are so many options available and partly because there can be significant differences in rock properties even among the same deposit types.
MARCH 8, 2013 TECHNOLOGY
An Autonomous Underwater Vehicle-towed magnetometer proves itself in rough weather. The technique could reduce costs and time to complete seabed surveys, with improved accuracies.
MARCH 8, 2013 APPLIED
Company borne out of an academic collaboration benefits both students and industry doing offshore UXO surveys in the North and Baltic Seas.
MARCH 8, 2013 APPLIED
The extensive Karoo Basin of South Africa may hold vast reserves of shale gas. A tectonic modeling project underway will help determine their production viability.
MARCH 8, 2013 LIBRARY
Fundamentals of Gravity Exploration, authored by Thomas R. LaFehr and Misac N. Nabighian, is a new publication now available from the SEG Book Mart. The book covers a full range of gravity-exploration topics, including first principles, field instrumentation and operations, rock densities and density contrasts, data reduction, methods of interpretation, and geologic examples. The subject matter includes inversion and an appendix on the Fourier transform.
MARCH 7, 2013 TECHNOLOGY
Geosoft presented new workflows for geological subsurface modelling at PDAC 2013 in Toronto, adding to its integrated platform for earth exploration. The workflows include 3D wireframing and interpretation tools that make the modelling of subsurface geology faster and more effective for mineral explorers.
Gravity surveys have a huge range of applications, indicating density variations in the subsurface and identifying man-made structures, local changes of rock type or even deep-seated structures at the crust/mantle boundary. This important one-stop book combines an introductory manual of practical procedures with a full explanation of analysis techniques, enabling students, geophysicists, geologists and engineers to understand the methodology, applications and limitations of a gravity survey. Filled with examples from a wide variety of acquisition problems, the book instructs students in avoiding common mistakes and misconceptions. It explores the increasing near-surface geophysical applications being opened up by improvements in instrumentation and provides more advance-level material as a useful introduction to potential theory. This is a key text for graduate students of geophysics and for professionals using gravity surveys, from civil engineers and archaeologists to oil and mineral prospectors and geophysicists seeking to learn more about the Earth’s deep interior.
Fundamentals of Gravity Exploration (Geophysical Monograph Series No. 17) covers a full range of gravity-exploration topics, including first principles, field instrumentation and operations, rock densities and density contrasts, data reduction, methods of interpretation, and geologic examples. The subject matter includes inversion and an appendix on the Fourier transform. This book will help students to efficiently gain knowledge and appreciation for the method, and it will provide experienced earth scientists with a valuable addition to their exploration libraries, both for reference and understanding of this important method.
Often not given its due in oil and gas geophysics, knowledge of basement geology can be critical to exploiting reservoirs including the unconventional.
by GRAHAM CHANDLER on JANUARY 24, 2013
There is an article in the last Earth Explorer issue: