Investigating the physics of electromagnetics over steel cased wells

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Investigating the physics of EM over steel cased wells Lindsey J. Heagy UC Berkeley LBL Geophysics Seminar March 27, 2019

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Motivation Subsurface injections (hydraulic fracturing) 2

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Motivation 3 Maxwell’s equations (quasi-static) time frequency constitutive relations Subsurface injections (hydraulic fracturing)

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Casing: overview ● Numerical modelling ● DC Resistivity ● Electromagnetics ○ Conductivity ○ Permeability 4

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Modeling electromagnetics on cylindrical meshes ● Finite volume discretization ○ cylindrically symmetric ○ 3D cylindrical meshes ● DC, FDEM, TDEM ● Open source ● Implemented in SimPEG 5 Heagy & Oldenburg, 2018

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Modeling electromagnetics on cylindrical meshes 6 Kaufman, 1990 Validating the physics ● Kaufman (1990): Charges, currents, electric ﬁelds ● Augustin (1989): magnetic permeability

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DC Resistivity: fundamentals ● Kaufman (1990), Kaufman & Whitman (1993), Schenkel & Morrison (1994) ● Cross-sectional conductance (S · m) ● Implications ○ Survey design ○ Approximating wells (to reduce computation) ○ Sensitivity in an inversion Modeling electromagnetics on cylindrical meshes 7 currents charges short well long well

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DC resistivity with steel-cased wells ● Casing integrity ○ Fundamental physics ○ Feasibility ■ Full break, partial flaw ○ Factors influencing detectability ■ Conductivity (casing, background) ■ Depth of flaw 8 (Heagy & Oldenburg, 2019)

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DC resistivity with steel-cased wells: casing integrity 9

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DC resistivity with steel-cased wells: data at surface Intact well 10 primary Secondary (ﬂawed - intact)

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DC resistivity with steel-cased wells ● Casing integrity ● Survey design considerations ● Detecting a target ○ Conductor, resistor ○ Electrical connection vs. not 11 Signal due to target resistor conductor

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Direct current resistivity with steel-cased wells: impact points Modelling 12 Survey Design

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Electromagnetics with steel cased wells: conductive 13

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Electromagnetics with steel cased wells: permeable 14 t = 5ms t = 10ms t = 1ms conductive permeable

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Electromagnetics with steel cased wells: permeable 15 conductive permeable

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Electromagnetics with steel cased wells: permeable 16

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Electromagnetics with steel cased wells: permeable 17 conductive permeable diﬀerence

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EM with steel cased wells: impact points, conductivity 18 Survey design: currents = galvanic + image + channeled

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EM with steel cased wells: impact points, permeability 19 t = 10ms permeable Forward simulation: ● interplay between conductivity and permeability ● poloidal currents in casing Survey design: ● Important to include permeability ● longer response through time conductive

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Open questions 20 ● Horizontal and deviated wells ● Infrastructure ● Scalability of numerical simulations ● Inverse problem ● ...

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Tools for interactive geophysics 21

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22 Oldenburg, BIRS 2016

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● 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

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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

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(Cockett et al., 2015)

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Implemented in Python! framework

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forward simulation Survey: Data collection and geometry Problem: Physics

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ﬁnite volume

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create a mesh

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discretize & solve continuous discrete

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Data Misfit Regularization Inverse Problem inversion elements

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inversion as optimization

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Modular, multi-physics 33 ● Magnetics ● Gravity ● DC Resistivity ● Induced Polarization (IP) ● Electromagnetics ○ Time ○ Frequency ○ With IP eﬀects ● Fluid Flow