Applicability of 1D and 2.5D marine controlled source electromagnetic modelling

Tehrani, A. Moradi; Slob, Evert

doi:10.1111/1365-2478.12019

Cited by 4 publications

(5 citation statements)

References 27 publications

(39 reference statements)

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“…In the context of offshore hydrocarbon exploration, inline CSEM responses from thin, deeply buried 2-D reservoirs can often closely match those from 3-D reservoirs whereas the corresponding 1-D model responses are usually significantly different (e.g. Tehrani & Slob 2013). Furthermore, 1-D models cannot reproduce the effects of seafloor topography that are possible with 2-D modeling (Li & Constable 2007).…”

Section: Introductionmentioning

confidence: 99%

MARE2DEM: a 2-D inversion code for controlled-source electromagnetic and magnetotelluric data

2016

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This work presents MARE2DEM, a freely available code for 2-D anisotropic inversion of magnetotelluric (MT) data and frequency-domain controlled-source electromagnetic (CSEM) data from onshore and offshore surveys. MARE2DEM parametrizes the inverse model using a grid of arbitrarily shaped polygons, where unstructured triangular or quadrilateral grids are typically used due to their ease of construction. Unstructured grids provide significantly more geometric flexibility and parameter efficiency than the structured rectangular grids commonly used by most other inversion codes. Transmitter and receiver components located on topographic slopes can be tilted parallel to the boundary so that the simulated electromagnetic fields accurately reproduce the real survey geometry. The forward solution is implemented with a goal-oriented adaptive finite-element method that automatically generates and refines unstructured triangular element grids that conform to the inversion parameter grid, ensuring accurate responses as the model conductivity changes. This dual-grid approach is significantly more efficient than the conventional use of a single grid for both the forward and inverse meshes since the more detailed finite-element meshes required for accurate responses do not increase the memory requirements of the inverse problem. Forward solutions are computed in parallel with a highly efficient scaling by partitioning the data into smaller independent modeling tasks consisting of subsets of the input frequencies, transmitters and receivers. Non-linear inversion is carried out with a new Occam inversion approach that requires fewer forward calls. Dense matrix operations are optimized for memory and parallel scalability using the ScaLAPACK parallel library. Free parameters can be bounded using a new non-linear transformation that leaves the transformed parameters nearly the same as the original parameters within the bounds, thereby reducing non-linear smoothing effects. Data balancing normalization weights for the joint inversion of two or more data sets encourages the inversion to fit each data type equally well. A synthetic joint inversion of marine CSEM and MT data illustrates the algorithm's performance and parallel scaling on up to 480 processing cores. CSEM inversion of data from the Middle America Trench offshore Nicaragua demonstrates a real world application. The source code and MATLAB interface tools are freely available at http://mare2dem.ucsd.edu.

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Section: Introductionmentioning

confidence: 99%

MARE2DEM: a 2-D inversion code for controlled-source electromagnetic and magnetotelluric data

2016

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“…A 4-layer offshore model with a 100-m thick hydrocarbon layer buried at a depth of 1 km in host sediments in 1 km water depth. 3D EM responses of disk-shaped hydrocarbon reservoir in marine sediment that 1D models are not appropriate when the shape of disk is not circular and its size is smaller in the cross-line direction than in the in-line direction (Tehrani and Slob, 2013).…”

Section: Disk Model Responsesmentioning

confidence: 99%

Three-dimensional electromagnetic responses of disk-shaped hydrocarbon reservoir in marine sediments

Jang

Kim

2014

Geosci J

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This paper presents a three-dimensional (3D) marine controlled-source electromagnetic modeling algorithm using primary fields for a homogeneous half-space to accurately account for airwave effects. This algorithm is validated with analytic solutions for 1D two-and four-layer models and numerical results from another 3D model. Using this code, we investigate the 3D electromagnetic responses of a 100 m thick, 5 km disk-shaped hydrocarbon reservoir buried at a depth of 1 km below the seafloor. From the numerical results, we can recognize that a 3D effect of the reservoir typically produces a transition zone in comparison with 1D model responses. The transition zone decreases with the airwave effect as the depth of water becomes shallow. As the source frequency increases, the sensitivity to the reservoir increases, whereas the amplitude decreases and falls at higher than 1 Hz below the current system noise floor. Broadside electric fields for a 10-km diameter disk model are only about 5% of in-line electric fields for the 5-km disk model. The Tequivalence is observed at such a low frequency of 1 Hz for the thin resistive tabular target, whose response varies almost linearly with the target thickness and resistivity even in the transition zone.

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“…In the presence of a 3D point source, a 1D formation model allows to reduce the dimensionality of the problem from 3D to the so-called 1.5D via a Hankel transform (or two Fourier transforms) (see, e.g., [12][13][14]). This 1.5D approximation can also be used to obtain an initial subsurface resistivity distribution from marine CSEM measurements [15].…”

Section: Introductionmentioning

confidence: 99%

Adjoint-based formulation for computing derivatives with respect to bed boundary positions in resistivity geophysics

2019

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In inverse geophysical resistivity problems, it is common to optimize for specific resistivity values and bed boundary positions, as needed, for example, in geosteering applications. When using gradient-based inversion methods such as Gauss-Newton, we need to estimate the derivatives of the recorded measurements with respect to the inversion parameters. In this article, we describe an adjointbased formulation for computing the derivatives of the electromagnetic fields with respect to the bed boundary positions. The key idea to obtain this adjoint-based formulation is to separate the tangential and normal components of the field, and treat them differently. We then apply this method to a 1.5D borehole resistivity problem. We illustrate its accuracy and some of its convergence properties via numerical experimentation by comparing the results obtained with our proposed adjoint-based method vs. both the analytical results when available and a finite differences approximation of the derivative.

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Applicability of 1D and 2.5D marine controlled source electromagnetic modelling

Cited by 4 publications

References 27 publications

MARE2DEM: a 2-D inversion code for controlled-source electromagnetic and magnetotelluric data

MARE2DEM: a 2-D inversion code for controlled-source electromagnetic and magnetotelluric data

Three-dimensional electromagnetic responses of disk-shaped hydrocarbon reservoir in marine sediments

Adjoint-based formulation for computing derivatives with respect to bed boundary positions in resistivity geophysics

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