Fully anisotropic 3-D EM modelling on a Lebedev grid with a multigrid pre-conditioner

Jaysaval, Piyoosh; Shantsev, D. V.; Ryhove, Sébastien de la Kethulle de; Bratteland, Tarjei

doi:10.1093/gji/ggw352

Cited by 51 publications

(9 citation statements)

References 39 publications

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“…The results were in good agreement with those obtained from a semianalytic 1D approach, thus confirming the accuracy and reliability of the simulation method. Arbitrary anisotropic media could be accurately simulated by using Lebedev grids (Davydycheva et al 2003;Jaysaval et al 2016).…”

Section: Forward Modellingmentioning

confidence: 99%

Interpretation of deep directional resistivity measurements acquired in high-angle and horizontal wells using 3-D inversion

Puzyrev

Torres‐Verdín

Calo

2018

Geophysical Journal International

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The interpretation of resistivity measurements acquired in high-angle and horizontal wells is a critical technical problem in formation evaluation. We develop an efficient parallel 3D inversion method to estimate the spatial distribution of electrical resistivity in the neighborhood of a well from deep directional electromagnetic induction measurements. The methodology places no restriction on the spatial distribution of the electrical resistivity around arbitrary well trajectories. The fast forward modelling of triaxial induction measurements performed with multiple transmitter-receiver configurations employs a parallel direct solver. The inversion uses a preconditioned gradient-based method whose accuracy is improved using the Wolfe conditions to estimate optimal step lengths at each iteration. The large transmitterreceiver offsets, used in the latest generation of commercial directional resistivity tools, 2 improve the depth of investigation to over thirty meters from the wellbore. Several challenging synthetic examples confirm the feasibility of the full 3D inversion-based interpretations for these distances, hence enabling the integration of resistivity measurements with seismic amplitude data to improve the forecast of the petrophysical and fluid properties. Employing parallel direct solvers for the triaxial induction problems allows for large reductions in computational effort, thereby opening the possibility to invert multiposition 3D data in practical CPU times.

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Section: Forward Modellingmentioning

confidence: 99%

Interpretation of deep directional resistivity measurements acquired in high-angle and horizontal wells using 3-D inversion

Puzyrev

Torres‐Verdín

Calo

2018

Geophysical Journal International

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“…; Um, Commer and Newman ; Koldan et al . ; Grayver and Bürg ; Puzyrev and Cela ; Yavich and Zhdanov ; Jaysaval et al., ; Qiu et al . ), perfectly matched layer absorbing boundary conditions (Mittet ; Li and Huang ; de la Kethulle de Ryhove and Mittet ; Hu et al .…”

Section: Introductionmentioning

confidence: 99%

A finite‐element time‐domain forward‐modelling algorithm for transient electromagnetics excited by grounded‐wire sources

Cai

et al. 2020

Geophysical Prospecting

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A B S T R A C TA three-dimensional finite-element time-domain forward-modelling algorithm is developed to simulate transient electromagnetics excited by grounded-wire sources. The main advantage of this finite-element time-domain algorithm is that full transmitting-current waveforms and complex-shaped sources resulting from topography can be directly dealt with in this algorithm. The models used to test this algorithm include a homogeneous half-space model, a stratified-medium model, the model of a complex conductor at a vertical contact and the Ovoid Zone massive sulfide deposit at Voisey's Bay, Canada. The homogeneous half-space model is used to determine the truncation boundary for a computational domain, and to compare with the electromagnetic responses excited by step-off, step-on and direct current waveforms. For the stratified-medium model, results demonstrate that full transmitting waveforms have strong effects on the observed electromagnetic responses. The model of a complex conductor at a vertical contact is designed for the grounded electrical source airborne transient electromagnetic method and is also used to examine the effectiveness of the broadside and inline configurations for such a vertical, thin plate embedded in the subsurface. The area of the Ovoid Zone massive sulfide deposit possesses non-negligible topography, the effects of which on the shapes of the grounded-wire sources must be taken into account when implementing the finite-element time-domain solver. The results show that both the broadside and inline electromagnetic responses are strongly affected by the massive conductive ore body.

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“…Jaysaval et al . () presented an algorithm based on the finite difference discretization of a Lebedev grid to simulate 3D electromagnetic fields in marine controlled‐source electromagnetic surveying.…”

Section: Introductionmentioning

confidence: 99%

“…Liu, Xu and Li (2018) presented an algorithm for a 3D electrically anisotropic earth using the finite element method. Jaysaval et al (2016) presented an algorithm based on the finite difference discretization of a Lebedev grid to simulate 3D electromagnetic fields in marine controlled-source electromagnetic surveying.…”

Section: Introductionmentioning

confidence: 99%

Three‐dimensional magnetotelluric responses for arbitrary electrically anisotropic media and a practical application

Xiao

Zhao

et al. 2018

Geophysical Prospecting

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Electrical anisotropy in earth media increases the complexity of magnetotelluric responses. Magnetotelluric models based on anisotropic media must be developed to fully understand observed data. This paper presents a three‐dimensional algorithm for calculating magnetotelluric responses of arbitrary anisotropic media in the frequency domain. Using a staggered‐grid finite difference method, the model space is discretized into rectangular blocks with electric fields on the edges of each block and the magnetic fields normal to the faces of each block. The electric field Helmholtz vector equation that considers a full 3 × 3 conductivity tensor is calculated numerically under two orthogonal polarizations. In calculating the boundary values on the four sides of the three‐dimensional anisotropic model, we adopt different procedures for calculating the two‐dimensional responses on the sides in the x and y directions. The responses for a layered anisotropic model and a three‐dimensional isotropic model calculated with this algorithm are compared with the corresponding analytical and numerical solutions, respectively. The comparisons show that the algorithm's approximations are highly precise for a wide frequency band. A typical two‐dimensional anisotropic model and a general three‐dimensional anisotropic model were also constructed, and their responses were calculated. These anisotropic models have ordinary structures but can produce phase rolling out of quadrant magnetotelluric responses, which indicates that considering electrical anisotropy may improve our interpretation of observed data. Using this algorithm, we can model the observed data from the northern Qaidam Basin in northern Tibet, where ultrahigh‐pressure metamorphic rocks are exposed along an old suture, and seismic anisotropy was indicated in neighbouring areas. The phase tensors of the magnetotelluric sites at this location show large skew angles, and the corresponding phase splits are distinct in the off‐diagonal impedance elements. Although the isotropic three‐dimensional electrical structure can model the profile data well, the structure shows a sequence of conductive and resistive bodies in the mid‐lower crust of the north Qaidam Basin, which is very spatially inhomogeneous, and a simple intrinsic anisotropic body can also produce similar surficial responses. Using the three‐dimensional anisotropic algorithm, we found an equivalent anisotropic replacement for this area. The results of the three‐dimensional anisotropy modelling of the magnetotelluric data from the northern Tibetan Plateau show the valuable applicability of the three‐dimensional anisotropic algorithm in testing the qualitative presumption of electrical anisotropy.

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Fully anisotropic 3-D EM modelling on a Lebedev grid with a multigrid pre-conditioner

Cited by 51 publications

References 39 publications

Interpretation of deep directional resistivity measurements acquired in high-angle and horizontal wells using 3-D inversion

Interpretation of deep directional resistivity measurements acquired in high-angle and horizontal wells using 3-D inversion

A finite‐element time‐domain forward‐modelling algorithm for transient electromagnetics excited by grounded‐wire sources

Three‐dimensional magnetotelluric responses for arbitrary electrically anisotropic media and a practical application

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