SCALEM

SCALEM

PRESENTATION OF SCALEM

(Strasbourg Consortium for Airborne and Land ElectroMagnetics) 

SCALEM aims to

  • extend the performance and range of applicability of EM methods
  • model EM data with other geophysical data (multi-physics)
  • explain EM processes at different scales, from the core plug to the regional model
  • strengthen the relationship between academia and industry in EM geophysics
  • promote good practice in EM geophysics through training
  • develop the next generation of EM geophysicists

Individual projects related to EM research in Strasbourg are currently supported by multiple funding agencies and industry partners. There is however hardly any funding available to pursue long-term, high-risk/high-reward projects. We plan to use the SCALEM sponsors’ contributions to support such projects.

The core team consists of full-time faculty from the University of Strasbourg, teaching at its internationally-recognized Engineering School (EOST) and doing research at Institut de Physique du Globe de Strasbourg (IPGS), one of Europe’s premier Earth-Science research institutions.

The core team member’s areas of technical expertise include Land and Airborne Electromagnetics, Ground-Penetrating Radar, Petrophysics, Rock Mechanics, DC Resistivity, Nuclear Magnetic Resonance with experience in applications such as Hydrocarbon, Mineral and Geothermal Exploration, Near-Surface Characterization, Hydrology, Volcanology, Archeology and Reservoir Monitoring.

No sponsor monies are allocated toward core staff support. Sponsors’ contributions (currently 18 kEUR/yr) go toward covering non-core personnel costs, such as research students, post-doctoral fellows and contractors, as well as administrative costs. We ask sponsors for an initial three-year commitment.

As sponsors to SCALEM, industrial partners will be able to

  • attend an annual two-day workshop, in Strasbourg or at another agreed locale, consisting of one day of oral presentations by SCALEM team members and one day allocated to training, either in the classroom or in the field
  • receive copies of reports, memoirs, oral presentations related to SCALEM-funded projects
  • have access to some (depending on licensing) of the developed codes within SCALEM projects

Interested partners can contact Pr. Marquis.

  

SCALEM projects planned for 2019-2022 include

 

  • Adding value to geophysical data with multi-physics joint inversion (Pr. Marquis)

Multi-physics interpretation and inversion has picked up in recent years. The most common use case in industry is for near-surface characterization. Several teams have been looking at integrating into the velocity model-building exercise some information from other types of geophysical data such as gravity, AMT, TDEM or airborne EM. A few successful examples have been published (e.g. Colombo et al., 2015, 2016; Marquis et al. 2016; Ogunbo et al. 2018; Pineda et al., 2015) but we are still at the early stages of the multi-physics characterization of the subsurface. 

    • Capitalize on the relative strengths of each method

Most published multi-physics inversions have been done by including a cross-gradient in the objective function. When things go right, the better-quality geometric information from the non-seismic data is used to constrain the velocity model, forcing it to adapt to the geometry. A good example of this is the water table, which is very well resolved by EM and thus provides a robust geometric constrain to the velocity model. We propose here, in addition to look at cross-gradients, to investigate the possibility of using joint sensitivities to exploit optimally the relative “strengths” of each geophysical method during the inversion. Our approach is gradual: first on different methods sampling the same physical property (e.g. AMT, DC, Surface and/or Airborne EM), then on combining properties (e.g. seismic/EM, gravity/EM). One expected outcome could be optimal survey design for joint inversion. 

    • Including scale in joint inversion with petrophysics

Some authors include a petrophysical term in the objective function, in which the inverted physical properties are to be kept close to a pre-defined petrophysical relationship. Well-logging data sample subsurface physical properties at similar scales, while surface geophysical data often do not. How do we include such sampling discrepancies in a joint inversion workflow? We propose here to simulate geophysical data based on sonic, resistivity and density logs, to appraise how the geophysics re-scales the log data and to build operators that include the re-scaling in the inversion workflow. 

    • How much artifact do we bring in when mapping between meshes?

In addition to pursue cross-gradient approaches as well as other joint inversion strategies, we also want to revisit the modelling strategy. The response of each geophysical method is computed with its own computational grid and the models are interpolated to a common grid, usually the one used for seismic data.  How much do the choice of mesh and the related interpolation influence the joint inversion, especially if it relies mostly on the cross-gradient? We expect this problem to be of importance if one wants to include MT data on the joint inversion workflow.

 

  • Magnetic Resonance Imaging in low porosity rocks (Pr. Girard)

In the last decades, surface nuclear magnetic resonance (SNMR also referred as MRS in 1D sounding) has been recognized as a reliable tool for groundwater resources exploration and management. Applicable in the first hundred meters of the subsurface, SNMR is nowadays applied in various geological contexts thanks to ongoing development sustained over the years to wider its field of application.

The MR signal amplitude is proportional to the liquid water volume and its decay time allows us to estimate the pore diameters, hence permeability. In low porosity context (hardrock or desaturated  zone for instance) the level of signal is low which makes it difficult to use practically.

A poor signal-to-noise (S/N) ratio close to urban zones has always been the main limitation of SNMR measurements (Legchenko & Valla 2003). To reduce MRS weakness to environmental and anthropogenic electromagnetic noise, one way is to reduce the noise level using heavy filtering protocols, recently including multichannel systems and statistical approach (e.g. Larsen et al. 2014; Muller-Petke & Costabel 2014). The state of the art industrial harmonic removal is not satisfying in many cases (Larsen & Behroozmand 2016). Indeed, these technics are highly dependent on the temporal and spatial variation of the surrounding noise and the efficiency of filtering is site dependent.

Another strategy is to increase the signal amplitude by changing the measurement protocols with new excitation sequences and loops geometries (Grunewald et al., 2016; Girard et al., 2018). In our team, we concentrate our efforts on the mitigation of the noise both on the hardware and software sides, on the filtering and measurement protocols. Our field activities with the hydrology Institute in Strasbourg been focused on fractured and weathered granite aquifers, we concentrate our efforts to obtain good results and reduce the duration of the measurements in a low porosity context. Further, any progress will impact the use of MRS in other geological contexts.

 

  • Rock Physics (Pr. Baud, Dr. Heap)
    •  Evolution of mechanical and transport properties during diagenesis using synthetic rock samples

Porosity exerts a first-order control on the mechanical and hydraulic properties of reservoir rocks. However, trends in plots of strength, electrical conductivity, and permeability as a function of porosity are obviously complicated by the fact that other microstructural parameters change with the porosity, such as the matrix composition and properties such as pore and grain size distributions. We propose to overcome this problem by using precisely controlled synthetic samples for which we exactly know and can design the microstructural geometries and the porosity. These samples will be prepared from known sizes or mixed distributions of spherical glass beads that will be sintered to create samples that can be measured in the laboratory. Pilot experiments showed that it is for example possible to reproduce Bourbié & Zinszner’s (1985) porosity-permeability data on Fontainebleau sandstone using such synthetic samples. Using these samples we can unravel the contribution of each microstructural attribute on the mechanical and transport (hydraulic and electric) properties of rocks. Our primary goal will be to quantify how progressive cementation will impact the elastic and non-elastic behavior of rocks, as well as physical properties over a wide range of grain sizes and grain size distributions. Constitutive models and new models for the evolution of electrical conductivity with deformation will be developed based on these new data. 

    • Time-dependent compaction in reservoirs

Chemical rock-fluid interactions occur in reservoir environments. Subcritical crack processes such as stress corrosion introduce a time-dependence that allows rock to deform and fail at lower stress over extended time. Our understanding of time-dependent failure in all rock types has improved significantly following series of experimentally driven studies (see for example, Heap et al., 2009). More recently, pilot studies in sandstones and carbonates (Brantut et al., 2014; Heap et al., 2015) showed that stress-corrosion could also induce significant time-dependent inelastic compaction at relatively high effective pressures. We therefore propose to study time-dependent compaction in selected sandstones and carbonates under a wide range of reservoir conditions Our goals will be: 1) to evaluate the influence of in situ conditions (pressure, temperature, fluid nature) on the strain rates and long-term evolution of the formations, 2) construct deformation maps quantifying the impact of different processes (stress corrosion, pressure solution, etc.), 3) quantify the impact of time-dependent compaction on physical properties with possible link to 4D seismic data.

 

Meet our Core Team 

Guy Marquis resumed his Professorship at the University of Strasbourg in early 2018. His current research interests are on the application of land and airborne electromagnetic methods to exploration problems with a focus on multi-physics inversion. He took a ten-year hiatus from academia to work as a Senior Geophysicist at CanAlaska Uranium in Vancouver, followed by a R&D position at the Shell Technology Center in Houston where he was also the SME for Land and Airborne EM, then as the Principal of EMinent Geophysics, a consultancy.

Jean-Francois Girard is a Professor at the University of Strasbourg. He is a geophysicist specialized in resistivity imaging and magnetic resonance sounding. He particularly worked on aquifer characterization for both water supply and industrial site remediation, on CO2 geological storage monitoring and on deep geothermal exploration. He has 30 papers in peer-reviewed international journals. His h-index is 14 (SCOPUS) and has been cited a total of 423 times. 

Patrick Baud is a Professor at the University of Strasbourg since 2009. His research interests are in Rock Physics and Rock Mechanics with focus on energy resources, environmental applications and natural hazards. He is studying both the phenomenological and micromechanical aspects of rock deformation and fluid flow using an approach integrating high-pressure deformation experiments, quantitative characterization of microstructure and theoretical analysis. He has 93 papers in peer-reviewed international journals (with 93 co-authors) and has been cited a total of 3166 times (SCOPUS). His h-index is 34 (SCOPUS).

Mike Heap is an experimentalist whose research focus is on the physical, mechanical, and transport properties of porous rocks. He is particularly interested in how deformation (brittle or ductile) and microstructural parameters (cracks, pores, pore-size, grain-size, amongst others) influence rock physical properties. He applies these data and models to better understand various geophysical (e.g., volcanoes and fault zones) and industrial (e.g., geothermal) problems. Mike has 90 papers in peer-reviewed international journals (with 137 co-authors) and has been cited a total of 1847 times (SCOPUS). His h-index is 26 (SCOPUS). 

Maksim Bano is an Associate Professor at the University of Strasbourg who specializes in seismic and ground propagating radar (GPR) methods, contributing on both theoretical and experimental aspects. He worked on the influence of water content on GPR responses and on the effects of grain size, grain shape and compaction on EM waves. He performed many studies in GPR imaging of buried active faults (New Zealand, Turkey and Mongolia) and in GPR response and FDTD modeling of hydrocarbon contamination in soils. He is also involved in several GPR investigations for archaeology and cultural heritage diagnostics (Turkey, Mexico). He is an Associate Editor of Geophysics. Maksim supervised five PhD and ten MSc theses since 2000 and authored more than 60 papers in international journals.