Presenter: Alberto Ardid Segura

Date: 18th August 2020

Time: 1300 AEST

Title: Lithologically-constrained stochastic magnetotelluric inversion for imaging shallow conductors in geothermal fields

Abstract:

Geothermal fields are usually explored by magnetotelluric (MT) surveys primarily to characterize a shallow conductor reflective of a conductive clay structure, commonly known as the clay cap. Standard deterministic MT inversions suffer from non-uniqueness and uncertainty, and the inclusion of useful lithological information is still limited. We develop a Bayesian 1D inversion method that integrates the electrical resistivity distribution from MT surveys with Methylene Blue (MeB) data, an indicator of conductive clay distribution in geothermal wells. The inversion seeks to infer under uncertainty the shallow conductor boundaries in geothermal fields. By incorporating borehole information, our inversion reduces non-uniqueness and then explicitly represents the irreducible uncertainty as estimated depth intervals for clay cap boundaries. This is particularly important when constraining the lower conductor boundary, as this feature is difficult to discriminate from the MT alone.

We apply the methodology to a set of 250 MT stations and 130 MeB profiles in the New Zealand Wāirakei geothermal field to estimate under uncertainty the conductor boundaries. Then, we compare the infer boundaries with the clay distribution, temperature logs and lithology from wells to estimate temperature gradients and conductive heat flux through the clay cap. By quantitative correlations among the different data sets, we present an unprecedented view into clay capping structures in high-temperature liquid dominated geothermal fields.

Bio:

Alberto is a MSc geophysicist who studied at the University of Chile, and is a current Doctoral candidate at the Geothermal Institute in the University of Auckland. His doctoral research is focussed on studying the electrical resistivity distribution in geothermal fields through Bayesian magnetotelluric inversions that allows assimilating data from different properties such as lithology and temperature, and quantifying uncertainty. Prior to that, Alberto’s research focused on shallow active and passive seismic exploration on geothermal systems. He also has industry experience mostly related to R+D in direct current, gravity and magnetic geophysical methods for mining and basin research.

To register, please go to this link: https://us02web.zoom.us/webinar/register/WN_qDrzV7GsQOKBtCnBApxeBQ

Title: Contemporary crustal stress pattern of Australia

Summary:

The present-day stress field of Australia has been the subject of great interest in the three past decades because it shows a variable pattern for the orientation of maximum horizontal stress (S_Hmax) that is not parallel to absolute plate motion. Analysis of in-situ stress data across Australia (in >20 sedimentary basins) reveals four major trends for the orientation of S_Hmax including NE-SW in northern, northwestern and northeastern Australia, E-W in southern half of Western Australia and South Australia, ENE-WSW in most parts of eastern Australia and NW-SE in southeastern Australia. In addition, the results reveal significant rotation of stress within various sedimentary basins due to the presence of different geological structures, including basement structures, faults, fractures and lithological contrasts. Understanding and predicting local stress perturbations has major implications for determining the most productive fractures in petroleum and geothermal systems, and for modelling the propagation direction and vertical height growth of induced hydraulic fractures in unconventional reservoirs.

Biography of the presenter:

Dr Mojtaba Rajabi is an ARC DECRA Fellow at the School of Earth and Environmental Sciences, University of Queensland. He has over 12 years of extensive experience in crustal stress analysis, reservoir geomechanics, geomechanical-numerical modelling and petrophysics. He graduated with a Ph.D. in Earth Sciences from the University of Adelaide in 2017. Dr Rajabi has worked on the geomechanical analyses of >30 sedimentary basins from across the world including Australia, New Zealand, Middle East, Mozambique, Iceland and Western Mediterranean. Since 2012, Dr Rajabi has worked on the Australian and World Stress Map projects. He has received >15 international awards and prizes for his research including the ARC-DECRA Award, the Australian SEG Early Achievement Award, EAGE Louis Cagniard Award, and the International Lithosphere Program’s Flinn-Hart Award.

The ASEG welcome you to join us on ZOOM on Tuesday 7 July, 4pm (AEST) for a talk by David Annetts from CSIRO.

Ten years in the wild (Redux)

An updated and expanded version of the AEGC presentation providing background to a CSIRO project that was placed in the public domain in 2009.  The talk offers lessons and guidance for others who would walk a similar path.

The use of open-source codes has become pervasive over the past 20 years but such codes are uncommon in minerals exploration. The P223 series of programs researching forward and inverse modelling of electromagnetic data was supported by CSIRO and six AMIRA consortia over 27 years and produced, amongst others, the codes, Airbeo, LeroiAir and Marco. This project concluded in 2008 and, after a two-year embargo, the code base, consisting of computer programs modelling different approximations of the earth for ground and airborne prospecting systems, was released to the public. We discuss reasons why codes have not been more widely adopted, and examine the evolution of some of the codes in research, academia and in industry as a guide to parties who would embark on a similar route.

David Annetts has been with CSIRO since 2007. A forward-modeller by inclination, he has researched the application of frequency and time-domain electromagnetic prospecting methods to marine CSEM, CO2 sequestration, uranium and groundwater exploration, and maintains an active interest in CSIRO’s Bayesian Lithological Inversion initiative.  He is also the current ASEG President.

Register Now: https://us02web.zoom.us/webinar/register/WN_wRoI_iXERlmmAA-wtXjHLw

After registering, you will receive a confirmation email containing information about joining the webinar.

Please join us on Tuesday 14^th July,  5pm (AEST) for a talk by Marina Costelloe from Geoscience Australia hosted by FedEx.

Mentoring through change, a perspective

Building on her experience as an ASEG President, STEM ambassador, and senior manager with Geoscience Australia, this talk is aimed at geophysicists at any stage in their career and will cover our shared leadership challenges, what we need to do more of, and less of, where to go to for help and how you can make the most of new opportunities for your workplace, your teams and for you in your own leadership sphere. There will be lots of time for questions and discussions.

Biography:

Marina Costelloe is the Director of the Onshore Seismic and Magnetotelluric Section within the Mineral Systems Branch at Geoscience Australia. Marina has worked in areas as diverse as mineral exploration, groundwater, critical infrastructure, earthquakes, and data science and contributed to international nuclear monitoring and space weather over the past 25 years. In 2018, Marina took on the role of President of the Australian Society of Exploration Geophysics (ASEG). Marina represents the Geology and Geography Cluster on the board of Science and Technology Australia and represents Australia on the Society of Exploration Geophysics Pacific Regional Affairs Committee.

Register Now: https://us02web.zoom.us/webinar/register/WN_quT25XVVTLGxJNTyy3XE_Q

After registering, you will receive a confirmation email containing information about joining the webinar. Contact secretary@aseg.org.au if you have any questions.  

Please bring your own drinks and nibbles.

Please join us on Wednesday 17^th June,  6pm (AEST) for a talk by Claire Mallard from USYD.

Coupling Surface Evolution and Mantle Dynamics: two examples of the interplay of Tectonics, Eustasy and Surface Processes

Over deep time, mantle flow-induced dynamic topography as well as plate tectonic evolution drive deposition moderated by higher-frequency fluctuations in climate and sea level. The effects of deep mantle convection and lithospheric deformation impact all the segment of the source to sink systems at different wavelengths and over various scales which remains poorly quantified. Field observations and numerical investigations suggest that the long-term stratigraphic record along continental margins contains essential clues on the interactions between dynamic topography and surface processes. However, it remains challenging to isolate the fingerprints of dynamic topography, lithospheric deformation, eustatic variation and climate change in the geological record.

In the first part of the talk, I will show you how we use a new numerical simulation package that couples the open-source surface evolution code Badlands (https://badlands.readthedocs.io/en/latest/) with lithospheric-scale thermo-mechanical models (https://uwgeodynamics.readthedocs.io/en/latest/) for unravelling the effect of rift obliquity on the distribution of facies and the evolution of stratigraphic architecture in syn-rift deposits.

The second part will focus on the integration of mantle convection simulation results into Badlands to quantify the impact of different timings and wavelengths of dynamic topography migration on the surface. I will present an example of the last 40 Ma evolution of the South African landscape.

The results suggest that our source-to-sink numerical workflow can be used to explore, in a systematic way, the interplay between dynamic topography and surface processes and can provide insights into recognizing the geomorphic and stratigraphic signals of dynamic topography in the geological record.

Register Now: https://us02web.zoom.us/webinar/register/WN_lf3ScLqiRCyGYll3gLcUnA

After registering, you will receive a confirmation email containing information about joining the webinar. Contact secretary@aseg.org.au if you have any questions.  

Please bring your own drinks and nibbles.

Date: Wednesday 15 July

Presenter: Indrajit G. Roy (PhD)

A link to the Zoom webinar will be shared closer to the event date.

Title: Computations methods in Geophysics

Abstract:

Mathematical derivatives, since their birth within calculus in the last quarter of seventeenth century, have been occupying a most important place in almost every sphere of science.  They are fundamental to geophysical modelling and particularly potential field data analysis, from data presentation through to quantitative interpretation. But the challenges of robust and precise estimation of derivatives along with their implementation are many. This presentation will review some of those challenges, how to minimize errors and provide insight into many of their applications.

Please join us on Thursday 25^th June, 12:00pm (AEST) for a talk by Sumit Verma from University of Texas of Permian Basin (UTPB).

Seismic Attribute Illumination of complex fault network North Slope, Alaska

The North Slope, Alaska has a complex fault system in the subsurface due to different episodes of tectonics. The most producing reservoirs are fault controlled. Our study area lies in the south of the well-known Prudhoe Bay and Kuparuk River oil fields. The Triassic-aged Shublik Shale, which is the most prominent source rock, has gone through three stages of extensional tectonic activities during the Jurassic, Cretaceous, and Eocene. To understand the complex fault system, we computed an ensemble of volumetric seismic attributes, including coherence, curvature and aberrancy, and studied them along the Shublik Shale surface. In this study, we have divided the structures into three types based on seismic signature, 1. significant fault throw on vertical seismic section, 2. insignificant fault throw but clearly visible flexure, 3. insignificant fault throw and very weak flexure. We observed type 1 faults on the vertical seismic section, and seismic attributes which trends in WNW direction, these faults have large lateral extent. The type 2 faults have similar orientation as type 1. The type 2 faults are clearly visible on the curvature and aberrancy attributes. Although, the type 3 structures have no visible throw on vertical seismic, but, it can be seen as two fault lineation (which are orthogonal each other) on curvature and aberrancy attributes. Based on our attribute analysis and regional geologic understanding, we believe that, the type 1 and type 2 fault sets are of Jurassic age, whereas the two faults of the type 3 were formed in Cretaceous and Eocene with an orientation of nearly east-west and north-south orientation. These type 1 faults display cross cutting, single-tip and double-tip abutting relations with the older west-north-west striking faults.

Biography:

Dr. Sumit Verma is an Assistant Professor of Geophysics at UTPB. Dr. Verma received his M.S. (2007) in Applied Geophysics from the Indian School of Mines - Dhanbad, and his Ph.D. (2015) in Geophysics from the University of Oklahoma. After earning his PhD, he worked for one year as a Postdoctoral Research Fellow at the University of Wyoming. Dr. Verma also worked with Reliance Industries Ltd. E&P for four years (2007-2011) as a development geoscientist. Dr. Verma’s research areas are Seismic Interpretation, Quantitative Interpretation and Reservoir Characterization. Dr. Verma is a deputy editor for the peer-reviewed scientific journal: Interpretation.

Register Now: https://us02web.zoom.us/webinar/register/WN_Myhly7WKS6uTu0wS9bldQw

After registering, you will receive a confirmation email containing information about joining the webinar. Contact secretary@aseg.org.au if you have any questions.  

Please bring your own drinks and nibbles.

Please join us on Thursday 11^th June, 2:00pm (AEST) for a talk by Anandaroop Ray

Probabilistic Seismic Full Waveform Inversion (FWI)

Register Now: https://us02web.zoom.us/webinar/register/WN_MBfv_1tRSeuLMq-7PvKI_Q

After registering, you will receive a confirmation email containing information about joining the webinar. Contact secretary@aseg.org.au if you have any questions.  

Please bring your own drinks and nibbles.

Probabilistic Seismic Full Waveform Inversion (FWI)

Limited illumination, insufficient offset, noisy data and poor starting models can pose challenges for seismic full waveform inversion (FWI). Appropriately formulated Bayesian approaches can mitigate these problems by appealing to parsimony, i.e., low model dimension, and through rigorous quantification of prior knowledge. Given the flexibility of the Bayesian framework, the theory can include the inference of nuisance parameters such as the source wavelet and data noise. Given the tandem developments in statistical inference and HPC, sampling based approaches to FWI are able to provide a surprising amount of subsurface information. While the non-linearity of wave physics is indeed a significant obstacle for inversion algorithms, it is also the reason why inferences, should we reach the appropriate local minima (or posterior probability maxima), are so much more informative than for diffusive or potential field geophysics. Through a combination of synthetic and real data examples, this talk will attempt to encourage further research in this arena.

Biography:

Anandaroop Ray (“Anand”) started his career as a non-seismic geophysicist with Shell Exploration and Production in 2007. In 2010 he joined the PhD programme in marine electromagnetics at the Scripps Institution of Oceanography in San Diego, California. In 2014 he completed his thesis focusing on uncertainty estimation in electromagnetic inversion for marine hydrocarbon exploration. From 2012-19, he worked for Chevron R&D on various problems – controlled source electromagnetics (CSEM), seismic full waveform inversion (FWI), reservoir properties from seismic (RPFS), airborne electromagnetics (AEM), statistical hydrocarbon exploration lookback analyses, and the role of machine learning in geophysics. The question most asked through his work is “how credibly can we interpret our inversion model(s),” the answering of which often requires the use of high performance computing (HPC) techniques. He currently co-advises a PhD student at Columbia University on Bayesian geophysical inversion, and has been active in convening and organizing the Uncertainty in Geophysical Inversion session at the American Geophysical Union’s Fall Meeting. In March 2019 he joined the Minerals, Energy and Groundwater Division at Geoscience Australia, where he continues to work on inverse uncertainty, model representation and geostatistics.

Branch hosting the event: SA/NT

Title: Searching for the Beaumont Children and Other Adventures in Unmarked Grave Detection

Presenter: Dr Ian Moffat

Date: Tuesday 2nd June 12:30 pm AEST

Abstract:

The reliable detection of unmarked graves is one of the most important challenges faced by community groups, industry and law enforcement agencies. Burials are ubiquitous in the archaeological and forensic record however these features are challenging to locate with conventional techniques. Geophysical methods are often used for this purpose due to their non-invasive nature and rapid site coverage however graves remain a difficult target due to their subtle response and small size. This presentation reviews a number of grave detection projects, including the search for the Beaumont Children and mapping WWII graves from the Battle of Tarawa, to discuss current best practice in this field.

Bio:

Ian Moffat is an ARC DECRA Senior Research Fellow in Archaeological Science at Flinders University where he undertakes research in the application of earth science techniques in archaeology. He has previously held research positions at the University of Cambridge and the Institute for Mediterranean Studies. Ian holds a PhD from the ANU and a BA and BSc (Hons) from UQ. In addition to his academic career he has worked at Ecophyte Technologies, Precipice Training and Archaeometry Pty Ltd.

The VIC Branch of the ASEG invite you to join us on ZOOM for the next talk in the ASEG Webinar Series.

Please join us on Wednesday 27th May, 6:00 pm (AEST) for a talk by Dr Rob Hewson, University of Twente, NL.

How remote is remote sensing from Geophysics?

The question of remote sensing’s place in the exploration tool kit has often raised questions, if not eye brows for many geologists / geophysicists. This talk provides a brief overview of the new and available satellite/airborne sensors and archived imagery, to add to this discussion – the advantages, caveats and relevance of it in the tool box. Examples include the AEGC2019 presentation of the multi-sensor and airborne geophysics case study over the Haib Cu porphyry deposit, Namibia.

Register Now: https://us02web.zoom.us/webinar/register/WN_tUhOokagSAK9h-HhK7m5Gw

After registering, you will receive a confirmation email containing information about joining the webinar.

Please bring your own drinks and nibbles.

Contact secretary@aseg.org.au if you have any questions. 

Rob has also requested that the below link be attached which will be discussed during the webinar.

https://2019.aegc.com.au/programdirectory/docs/224.pdf