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open source simulations and inversions in geoph...

Lindsey Heagy
November 02, 2016

open source simulations and inversions in geophysics

Geophysical inverse problems are used to estimate models of the subsurface from a finite number of data collected over the earth. SimPEG (Simulation and Parameter Estimation in Geophysics, http://simpeg.xyz) is a collaborative effort to develop an open source framework for solving geophysical simulation and inversion problems, including electromagnetics, vadose zone flow, and potential fields, in a consistent manner. The goal in the development of SimPEG is to support a community of researchers with well-tested, extensible tools, and encourage transparency and reproducibility both of the SimPEG software and the geoscientific research it is applied to. Using an example from applied electromagnetics: monitoring an injection (such as a hydraulic fracturing) from a steel cased well, I will provide an overview of the framework and discuss some of the strategies we are using to promote collaboration. I will also discuss how we have re-purposed the numerical tools in SimPEG to build web-based interactive simulations for students to explore fundamental concepts in geophysics (http://geosci.xyz).

Lindsey Heagy

November 02, 2016
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  1. open source simulations and inversions in geophysics Lindsey Heagy with

    Rowan Cockett, Seogi Kang, Doug Oldenburg, Gudni Rosenkaer, Dom Fournier, et al Geophysical Inversion Facility University of British Columbia
  2. • Context: an applied EM problem ◦ An example: steel

    casing • Big picture: simulations and inversions in geophysics ◦ What are the pieces? • Framework & Toolbox ◦ How do we implement this? • Building in the open ◦ What can I do with it? ◦ Collaborative development • Interactive geophysics ◦ Teaching with numerical simulations outline
  3. em + steel casing This is a problem. Want to

    characterize this (SEG Abstract: Heagy et al, 2015) Physical Properties • highly conductive • significant (variable) magnetic permeability Geometry • cylindrical • thin compared to length
  4. • Fields magnetic flux density current density • Physical Properties

    • Fluxes Constitutive Relations Maxwell’s Equations (quasi-static) electric field magnetic field electrical conductivity magnetic permeability Time Frequency math!
  5. grounded electric Physics: Maxwell’s Equations Physical Properties electrical conductivity magnetic

    permeability anisotropy... Meshes 2D Cylindrical Sources inductive loop primary-secondary Data & Sensitivities … and Time Frequency 3D custom pieces: simulation
  6. building for researchers • Flexibility to experiment • Integration of

    information ◦ Geologic ◦ Multiple physics • Reproducible and transparent
  7. • Modular: building blocks ◦ organized in a framework ◦

    pieces available to manipulation • Declarative: express intent ◦ write what you mean ◦ looks like the math • Extensible: new research ◦ quantitative communication ◦ built in feedback loops • Open: for the future ◦ reproducible ◦ opportunities for collaboration building for researchers
  8. building for researchers • Modular: building blocks ◦ organized in

    a framework ◦ pieces available to manipulation • Declarative: express intent ◦ write what you mean ◦ looks like the math • Extensible: new research ◦ quantitative communication ◦ built in feedback loops • Open: for the future ◦ reproducible ◦ opportunities for collaboration
  9. • Fields • Fluxes • Physical Properties discretize electric field

    magnetic field magnetic flux density current density electrical conductivity magnetic permeability
  10. ?

  11. Model & Physical Properties: What should we invert for? (SEG

    Abstract: Kang et al, 2015) Derivatives using chain rule: or : • Active reservoir layer • Parametric representation • ... inversion model physical properties
  12. ?

  13. grounded electric inductive loop point dipole (electric or magnetic) fields

    from a primary problem natural source Sources: How do we excite the Earth?
  14. ?

  15. Solve 2nd order system Solve E-B, H-J ? or and

    compute derivative Physics: How do we solve Maxwell’s equations
  16. ?

  17. compute fields everywhere: what we solved for from source derivative

    Fields: How do we calculate the EM fields and fluxes? from source from physics
  18. ?

  19. for example: casing & sensitivities What is the sensitivity with

    respect to the… • conductivity of the ◦ Block? ◦ Layer? ◦ Background? • Depth and thickness of the layer? • Location and widths of the block? Heagy et al. 2016 - in review
  20. for example: casing & sensitivities What is the sensitivity with

    respect to the… • conductivity of the ◦ Block? ◦ Layer? ◦ Background? • Depth and thickness of the layer? • Location and widths of the block?
  21. summary • Modular, composable pieces ◦ Compartmentalize concerns ◦ All

    pieces available to manipulation → extensible • Testing! ◦ Test pieces ◦ Test composite http://www.flickr.com/photos/13403905@N03/2080281038/
  22. Airborne Time Domain EM Inversion Figure above shows plan views

    of (a) the true conductivity model and (b) the recovered model, and section views of (c) the true and (d) the recovered conductivity models. Figure to the left shows observed and predicted data. Core cell size: 50×50×20 m, The number of cell: 50×50×48 = 120,000; Reference model: Half-space model with conductivity value, 0.005 S/m; Inexact Gauss-Newton: 13 iterations; Cpu time: 48hrs; Maximum memory usage: 51.2GB; Cpu:Intel(R)Xeon(R) CPU 2.80 GHz; Ram: 64 GB
  23. • Creating a toolbox and framework for geophysics • Focusing

    on flexibility and speed for the researcher • Starting to build a community