BCGS Technical Talk – April 18, 2019

Speaker: Kevin Fan, B.Sc., UBC

Title: Humanitarian Geophysics in Myanmar: Partnering with Local Governments and Universities to Alleviate Seasonal Droughts

Date/Time: Thursday, April 18, 2019 @ 4:30pm PST

Location: 4th Floor Conference Room, Room 451, 409 Granville St. (UK Building at Granville and Hastings), Vancouver

Abstract:

BCGS Technical Talk – March 28, 2019

Speaker: Dr. James Macnae, RMIT University, Melbourne, Australia

Title: Can machine learning, AI, analytics and the IoT add to AEM processing and interpretation?

Date/Time: Thursday, March 28, 2019 @ 5:00pm PST

Location: 4th Floor Conference Room, Room 451, 409 Granville St. (UK Building at Granville and Hastings), Vancouver

Abstract:

Can machine learning, AI, analytics and the IoT add to AEM processing and interpretation?
James Macnae, RMIT University

Some recent papers in computer science related to the “Internet of Things” (IoT) have presented examples of detecting anomalies in IoT time series using deep (machine) learning.  These examples have some elements in common with AEM data processing and interpretation, and may in the future lead to automated QC and first pass physical property prediction and ultimately geological interpretation.  However, implementing and setting up such processes will still be a very significant challenge for geoscientists. I therefor suspect that the Australian mineral explorer that last year made its geologists and geophysicists redundant, and advertised for “data mining specialists” will be too far ahead of its time.

To extract “useful” physical property information from this mountain of data, and thereby infer useful geology, there are many options. The historically most useful process combines physical insight to infer conductivity from the observed response with statistical methods to improve signal/noise. For example, EM data from a controlled source survey are presented as profiles or inverted with logarithmic time spacing, sensible for EM diffusion. Reduced noise has come from e.g. binary stacking, and recognition that sferic source energy is non-stationary and can usefully be “pruned” from the data before stacking.  Subsets of the acquired data are then selected, modelled and inverted based on simple models or a-priori assumptions. Questions remain as to whether commonly applied a-priori assumptions are reasonable, whether all the useful implications of the data, such as induced polarization (AIP) and superparamagnetic (ASPM) effects have been extracted, and whether sferics, powerline signals and VLF can provide complementary conductivity information in a controlled source survey.

Electromagnetic (EM) data is being collected at ever higher streaming rates, with airborne AEM data sampling rates approaching 1 MHz in some systems, and ground penetrating radar (GPR) sampling approaching 1 GHz. Six hours of data acquisition with BIPTEM, a 24-bit, 12 channel AEM system (6 B field sensor, 3 dB/dt, 3 rotation rate), each channel sampled at 156250 Hz will deliver over 150 GB of data.

The BC Geophysical Society will be hosting Dr. James Macnae, the inaugural Len and Genice Collett Distinguished Visiting Lecturer in Geophysics, who will be presenting a half-day short course titled:

“Integrated interpretation of airborne electromagnetic surveys: Determination and use of appropriate geophysical models”

Dr. James Macnae, RMIT University, Melbourne, Australia.

This half-day (AM) course will cover:

1)      The basics of geophysical electromagnetics (EM), time and frequency domain
2)      Airborne EM systems, trade-offs and recent advances
3)      The physical limits of conductivity resolution with AEM
4)      Detectable geology: Earth conductivity variations
5)      Consideration of computed geophysical models, direct and inverse

• Stitched 1D for quasi-layered environments
• 2D and 2&1/2D
• 3D, parametric and voxellated

6)      Case histories: Using computed AEM models to guide geological interpretation: Successes, limitations and failures
7)      Where might AEM be in 10 years?

REGISTRATION IS OPEN
(Deadline 5:00pm, Tuesday, March 26, 2019)

Payment will be accepted through PayPal. Click on the “Pay Now” button below.

To register as a student, please email us at info@bcgsonline.com.

BCGS Technical Talk – February 20, 2019

This month we have two exciting speakers.

1. Sarah Devriese, Condor North Consulting
2. Shawn Letts, Anglo American plc

Date/Time: Wednesday, February 20, 2019 @ 4:30pm PST

Location: 4th Floor Conference Room, Room 451, 409 Granville St. (UK Building at Granville and Hastings), Vancouver

Title & Abstracts:

Sensitivity-based data reduction of large 3D DC/IP Surveys
Sarah G. R. Devriese*, Robert Ellis, Ken E. Witherly, Condor North Consulting ULC, Geosoft

Survey companies are increasingly favouring large 3D DC resistivity (DC) and induced polarization (IP) surveys to aid in exploration programs. We present a sensitivity-based data winnowing algorithm that can reduce the amount of data from 3D DC/IP surveys to decrease the inversion computation time but retain similar levels of resolution in the final model. The method is based on the sensitivity of the data to the model space and designed to retain equal sensitivity coverage throughout the model space. The algorithm is tested on both synthetic and field examples.

Interpretation and Benefits of Full-Tensor Squid-Magnetometer Data
 Shawn Letts^1* Joel Jansen¹, Louis Polomé³, Anre Vorster^2
1Anglo American plc
²De Beers Group of Companies
³Spectrem Air Pty Ltd

Anglo American and De Beers have been supporting the development of low-temperature Super-conducting Quantum Interference Device (SQUID) magnetometers for over 15 years, with most of the research undertaken by the Leibniz Institute of Photonic Technology (IPHT) in Jena, Germany.  This partnership lead to the development of a TEM sensor able to measure precisely the late-time step-response of the earth.  The principal advantages of SQUID sensors for TEM surveys are: direct measurement of the magnetic field (hence the step-response of a transmitted square-wave), high magnetic field resolution at low frequencies, and a flat frequency response from DC to 10kHz.

Early research also focussed on passive magnetic-field measurements, including the development of a Full-Tensor Magnetic Gradiometer (FTMG).  Advantages of measuring the full tensor over the total-field include:  higher spatial resolution; a five-fold increase in information about the earth’s magnetic field, including information about magnetic remanence; and insensitivity to diurnal effects.

Standard cryogenic Dewars (cryostats) are vertical cylinders for ease of use, but this shape is not optimal for airborne surveys owing to the high-drag of the vessel.  To overcome this drawback, De Beers and Anglo American funded IPHT to develop and construct a horizontal-cylinder cryostat that easily and aerodynamically fits into a fixed-wing pod or a conventional rotary-wing towed bird.  The new system was trialed by De Beers over four projects during 2018, totaling ~ 17,000 line-km.
The results of these surveys corroborate the advantages predicted by forward modelling, being increased spatial resolution and a much-improved interpretational capability of the causative geology.  The accompanying presents survey results from a highly complex terrain in southern Africa to illustrate the aforementioned advantages of FTMG.

Interpretation of gravity and magnetic data: from geophysics to geology
A short course offered in collaboration with the BCGS

Presented by: Dr. Yaoguo Li
Centre for Gravity, Electrical, and Magnetic Studies,
Department of Geophysics, Colorado School of Mines

A 1-day short course presenting the state of art and practice in 3D inversion-based quantitative interpretation of gravity and magnetic data. With a focus on mineral exploration the course will present the basic concepts of 3D inversion and discuss the interpretation of gravity, gravity gradient, and magnetic data to extract geologic information,

Course Flyer: Poster_Yaoguo_ShortCourse_v2.pdf

A recent article in The Leading Edge by Dr. Yaoguo Li discusses the importance of quantitative geophysical interpretation in mineral exploration indicated by the below quote.
(Li, et al., The Leading Edge, January 2019, Vol. 38. No. 1: pp. 60-66.)

Article: YaoguoLi_2019_TLE.pdf

Furthermore, what is required is a mindset that may be described by the following adage: “No one cares about geophysics unless it can solve geology problems.” Thus, the focus should be on geology and not necessarily on geophysics by itself. Adopting this mindset logically requires geophysicists in research and practice to think and act as geoscientists with some understanding of the geologic and mineral systems in which we explore, of mineralogy, and of geochemistry. Consequently, we cannot focus primarily on geophysical methods in a semivacuum setting.”

REGISTRATION NOW AVAILABLE
(Deadline 12:00pm, Wednesday, Jan 23, 2019)

Payment will be accepted through PayPal. Click on the “Pay Now” button below.

Course Outline:

Gravity and magnetic data are among the most widely available geophysical data in mineral exploration and arguably have the most extensive areal coverage among all geophysical data with large depths of investigation. 3D inversion techniques have emerged as a major tool kit in the quantitative interpretation of these data over the last two decades. The ability to reconstruct the distribution of density or magnetic properties in various geological units through inversions has shifted interpretations from the data domain to the model domain and, thereby, transformed the interpretation from bump hunting in data displays to imaging structure and composition in 3D representations of the subsurface. More recently, the integration of inversion techniques is also poised to make major contributions to the emerging field of geology differentiation, which seeks to differentiate and characterize different lithology units, mineralized zones, or alteration zones by constructing quasi-geology models.

This course presents the state of art and practice in 3D inversion-based quantitative interpretation of gravity and magnetic data. The course will review the data acquired for mineral exploration with focus on newer data types, present the basic concepts of 3D inversion and the use of inverted models in the interpretation of gravity, gravity gradient, and magnetic data to extract geologic information, and demonstrate the power of integrated interpretation through joint inversion with petrophysical constraints and geology differentiation. The six topic areas covered in the course are as follows:

– Basic Theory: magnetic, gravity, and gravity gradiometry data in mineral exploration
– 3D Inversion: A means to image subsurface geology
– Gravity and Gravity Gradiometry: data processing and case studies
– Remanent Magnetization Inversion: new information about geology
– Joint Inversions: connecting to geology through property data
– Geology Differentiation: moving geophysics to geology interpretation

Dr. Yaoguo Li is a Professor in the Department of Geophysics at the Colorado School of Mines, and Director of the center for Gravity, Electrical and Magnetic Studies (CGEM). He currently leads the Gravity and Magnetics Research Consortium (GMRC) sponsored by the petroleum and mining industry. He is specialized in geophysical inversion methods for potential-field, DC/IP, and electromagnetic data and in geology differentiation with a focus on applications in mineral and petroleum exploration and production. He is an Associate Editor for the journal GEOPHYSICS. He is a member of AGU, EAGE, and SEG.