Speaker: Guillaume Rongier
Date: Thursday 13th of July 2023, 1:15pm.
Abstract:
Recent developments in deep learning have turned the spotlight on the entire field of machine learning. This has led to more and more studies comparing predictions from geostatistical and machine learning methods, sparking debates about whether machine learning will take over geostatistics in geological applications. This implicitly implies an opposition between those two fields. In this context, a statement made by Williams in 1998 contains an intriguing perspective: "In the Bayesian approach to neural networks, a prior on the weights of a network induces a prior over functions. An alternative method of putting a prior over functions is to use a Gaussian process (GP) prior over functions. This idea has been used for a long time in the spatial statistics community under the name of 'kriging' although it seems to have been largely ignored as a general purpose regression method." If the method known as kriging in geostatistics is the same as the method known as Gaussian processes in machine learning, how is it that geostatistics and machine learning are so often introduced as contending fields? Can we find similar relationships with more recent geostatistical approaches such as multiple-point simulation? What does this mean for the future development of both fields? This talk will deconstruct the idea that geostatistics and machine learning are two completely separate fields: their methods share a lot more similarities than usually acknowledged, and geostatistics can be seen as a sub-field of machine learning specialized on predictions with spatial data. Since 1998, Gaussian processes have become an integral part of machine learning, and both fields stand to gain from further exploring their similarities.
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- Category: Seminar
Speaker: Giusi Ruggiero
Date: Thursday 15th of June 2023, 1:15pm.
Abstract:
Uncertainty quantification in seismic imaging is important for a proper interpretation of the structural elements (e.g., faults and horizons) within the investigated subsurface. Especially in seismic full-waveform inversion (FWI), which is a highly non-linear problem and hence prone to non uniqueness, evaluate uncertainties associated with the estimated subsurface parameters is essential for interpreting inverted models. In this work, we first address uncertainty estimation in elastic FWI by calculating the posterior covariance matrix based on the data-misfit Hessian matrix. In particular, in order to make the computation tractable for large scale problems, we rely on a low rank approximation of the Hessian, which avoids the prohibitive computation of the full matrix. The resulting estimate of uncertainties will be used in a comparison between the homogenized FWI model and a set of homogenized geological models for seeking the best among multiple possible structural interpretations of a given seismic image.
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- Category: Seminar
Speaker: Enrico Scarpa
Date: Thursday 6th of July 2023, 1:15pm.
Abstract:
This seminar will mainly consist of a review and explanation of some field observations depicted from well-exposed outcrops in deep-water systems. It’s based on several papers about turbidite channels and one by Bell, Kane, Pontén, Flint, Hodgson & Barrett (Marine and Petroleum Geology 2018), entitled: "Spatial variability in depositional reservoir quality of deep-water channel fill and lobe deposits ". The full paper is available at Marine and Petroleum Geology.
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- Category: Seminar
Speaker: Noémie Fayol
Date: Thursday 8th of June 2023, 1:15pm.
Abstract:
Dans le cadre des travaux de la Chaire Industries Minérale & Territoires, on se propose d’étudier en particulier les interactions à l’œuvre autour de l’extraction des ressources minérales. En s’appuyant sur un cas concret d’exploitation de l’amiante au Québec, nous mettons en parallèle l’évolution de l’activité extractive et du territoire minier habité depuis la découverte du minerai et naissance de la communauté jusqu’à aujourd’hui. Nous verrons ainsi en quoi les interactions sociogéologiques et sociotechniques à l’œuvre dans l’histoire d’un territoire minier influent sur la résilience de celui-ci au cours du temps.
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- Category: Seminar
Speaker: Iman Rahimzadeh Kivi
Date: Thursday 29th of June 2023, 1:15pm.
Abstract:
Widespread deployment of CO2 capture and storage (CCS) in deep geological formations is identified as an essential component of any efforts to mitigate the climate change crisis. Most assessments conclude that CO2 storage rates in the order of several gigatons per year will be needed to achieve carbon neutrality by 2050. However, concerns exist about the long-term fate of CO2 underground and the possibility of leakage back to the surface. I will present research that investigates what would happen to CO2 injected at climate-relevant rates of gigatons per year over geological time scales (million years), much longer than any assessments performed so far. I will discuss the subsurface CO2 dynamics that can be simplified without loss of generality to vertical CO2 flow and transport concerning long-term CO2 migration through geological layers. Such a model enables us to draw reliable constraints on the CO2 leakage potential over geological time scales at affordable computational costs. Simulation results show that repetitive layering of caprocks, even if pervasively fractured and a few tens of meters thick, will significantly reduce the CO2 leakage risk, ensuring a secure road toward achieving climate targets.
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- Category: Seminar
Speaker: Lachlan Grose
Date: Thursday 1st of June 2023, 1:15pm.
Abstract:
One of the greatest challenges facing modern society is to reduce our impact on the environment. To do this we need to improve our management of the natural resources used for renewable and sustainable technologies (critical metals, base metals and water). We need to be able to make informed decisions about the subsurface, by understanding the subsurface geometry of geological features. We need to be able to make geologically consistent predictions (models) about the sub-surface geology at multiple scales. Geologically consistent models at the mine scale should equate to better understanding of natural resources and consequently a more economic and sustainable way of producing the required resources for a greener future with increased recovery rates and reduced amount of resources required and waste produced. We present the current state of the Loop project, an open-source interoperable, integrative, probabilistic 3D geological modelling platform. Loop applies new algorithms to use all structural geological data (e.g.: fault kinematics, fold axial surfaces, fold axes, deformational overprinting relationship) in the modelling process. These new algorithms require estimates of geologically relevant parameters (fault displacement, fold wavelength, intrusion shape etc). Estimating these parameters is not trivial and the solutions are usually non-unique. We propose using Bayesian inference to investigate these parameters using localised geological and geophysical inversions of specific structures.
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- Category: Seminar
Speaker: Guillaume Caumon
Date: Thursday 25th of May 2023, 1:15pm.
Abstract:
Sedimentary strata are essential archives of the past conditions of the earth, and host significant natural resources in the subsurface. However, inferring the features of strata at depth (e.g., geometry, connectivity, physical or geological properties), remains a challenge prone to many uncertainties. Classically, the layers and their geometry are first interpreted from boreholes, geological outcrops and geophysical images, then layer properties can be addressed with geostatistical techniques and inverse methods. Theoretical models considering horizon depth uncertainty have been proposed decades ago, and geostatistical simulation can sample petrophysical uncertainties, but these approaches leave the number of layers fixed and are rely on conformable layering assumptions which are seldom met. We review some recent developments in well correlation in the frame of relative chronostratigraphy, which addresses the problem of locating potential gaps in the stratigraphic record. We also present some first results of the integration of the number of layers in inverse problems using a reversible jump Monte Carlo method. These two elements open interesting perspectives to jointly address topological, geometrical and petrophysical uncertainties at multiple scales in sedimentary basins. Although such uncertainties can have significant impact on quantitative geological and geophysical model forecasts, many computational challenges still lie ahead to appropriately sample uncertainties. Harnessing these challenges should open the way to finding, on a case-by-case basis, the suitable level of detail between detailed stratigraphic architectures and effective medium representations.
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- Category: Seminar
Speaker: Eric Galin
Date: Thursday 22nd of June 2023, 1:15pm.
Abstract:
Modeling realistic and controllable large-scale landscapes is essential for creating virtual worlds. The challenge stems not only from the complexity of landforms, the variety of details and patterns at different scales, the need for geomorphological and hydrological realism, and the complexity of ecosystems but also from the need to control the shape and location of landforms to follow the designer’s intent. In this talk, I will present some recent research that aims at bridging the gap between simulation providing realism and interactive editing giving control.
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- Category: Seminar