Inversion of controlled‐source electromagnetic data using a model‐based approach

Abstract

A B S T R A C TA two-and-half dimensional model-based inversion algorithm for the reconstruction of geometry and conductivity of unknown regions using marine controlled-source electromagnetic (CSEM) data is presented. In the model-based inversion, the inversion domain is described by the so-called regional conductivity model and both geometry and material parameters associated with this model are reconstructed in the inversion process. This method has the advantage of using a priori information such as the background conductivity distribution, structural information extracted from seismic and/or gravity measurements, and/or inversion results a priori derived from a pixel-based inversion method. By incorporating this a priori information, the number of unknown parameters to be retrieved becomes significantly reduced. The inversion method is the regularized Gauss-Newton minimization scheme. The robustness of the inversion is enhanced by adopting nonlinear constraints and applying a quadratic line search algorithm to the optimization process. We also introduce the adjoint formulation to calculate the Jacobian matrix with respect to the geometrical parameters. The model-based inversion method is validated by using several numerical examples including the inversion of the Troll field data. These results show that the modelbased inversion method can quantitatively reconstruct the shapes and conductivities of reservoirs.

Object-based model verification by a genetic algorithm approach: Application in archeological targets

“…Başokur and Akça (2010), Elwaseif (2010) and Li et al (2010) have used cell-based models and conventional inversion techniques based on Hessian and gradient matrices to derive a background and/or general resistivity distribution. Elwaseif (2010) applied image processing techniques to the intrinsic resistivity section to outline the target body by using the geometries of resistivity anomalies.…”

“…However, the response of the delineated target is not compared with the measured data in the final step. Li et al (2010) defined a regional resistivity model by using polygons and sharp boundaries embedded into a 2D cell-based model obtained from a regularized inversion scheme. This method requires structural information from the other sources such as gravity and seismic measurements to be incorporated.…”

“…Therefore, the geometry of the units must be delineated by a human interpreter in the final model. The polygon model is used to define sharp boundaries (geological prospects) that are described by polygon vertices (Li et al, 2010;Olayinka and Yaramanci, 2000). The inverted parameters are the resistivity values of predefined regions and the coordinates of their vertices (Fig.…”

“…For example, a 2D layered earth model consisting of interfaces can be useful in hydrogeological and engineering geology problems (Akca and Başokur, 2010). A polygon parameterized by the coordinates of some of the vertices can be used to describe the 2D prospects (Li et al, 2010). Such models can reconstruct the shapes and resistivity values of target reservoirs in petroleum exploration, and they could also be used in mining exploration to outline ore bodies.…”

SimPEG: An open source framework for simulation and gradient based parameter estimation in geophysical applications

“…Physical property measurements can be used to assign upper and lower bounds for a physical property model at points in a volume or in various regions within our 3D volume. The various types of information that are relevant to the geologic and geophysical questions to be addressed must be combined and translated into useful information for the inversion (Lelièvre et al, 2009;Li et al, 2010).…”