ABSTRACT Steel well casings in or near a hydrocarbon reservoir can be used as source electrodes time‐lapse monitoring using grounded line electromagnetic methods. A requisite component of carrying out such is the capability to numerically model response set finite length. We present modelling algorithm finite‐element method for calculating three‐dimensional conductivity excited vertical steel‐cased borehole source. The based on combination moments and Coulomb‐gauged primary–secondary...

Abstract Magnetotelluric (MT) method is widely used for revealing deep electrical structure. However, natural MT signals are susceptible to cultural noises. In particular, the existing data-processing methods usually fail work when data contaminated by persistent or coherent To improve quality of collected with strong ambient noises, we propose a novel time-series editing based on improved shift-invariant sparse coding (ISISC), data-driven machine learning algorithm. First, redundant...

We have developed an edge-based finite-element (FE) modeling algorithm with a divergence correction for calculating the controlled-source electromagnetic (CSEM) responses of 3D conductivity earth model. solve curl-curl equation to directly calculate secondary electric field eliminate source singularity. The choice FE method enables us properly handle discontinuity normal component fields across boundaries. Although we can resulting complex-symmetric linear system equations efficiently by...

The galvanic distortion induced by the electric charge buildup across near-surface inhomogeneities can severely affect interpretation of magnetotelluric (MT) data for deeper structures. In addition to methods already available, we have developed an alternative approach processing MT impedance with such distortions using equivalent source technique. One prerequisite method is that all are acquired on surface, which nearly always case in land-based surveys. works field scaled from and...

In the traditional framework of 3D controlled-source electromagnetic (CSEM) modeling, either field formulation or coupled potential is implemented. We have developed an improved algorithm that can calculate CSEM responses based on a joint application secondary and formulations. The vector finite-element method implemented for discretization curl-curl equation field. nodal elements are simultaneously formulation. use stiffness matrix resulting from to construct efficient preconditioner, which...

We developed a 3-D joint modeling algorithm of controlled source electromagnetic (CSEM) responses with unstructured meshes. The crucial component is to construct an approximating matrix from the stiffness based on coupled potential formulation. Through incomplete Cholesky decomposition and application mapping connecting secondary electric fields potentials, we obtain efficient preconditioner for iterative solution linear system field first demonstrate accuracy by comparison analytic...

Summary The steel well casings near a hydrocarbon reservoir could be used as source electrodes in time-lapse monitoring using grounded line electromagnetic methods. An essential requisite of carrying out such is the capability numerically modeling response due to excitation by finite lengths. We present algorithm element calculate responses three-dimensional conductivity model excited with vertical steel-cased well. method combination moments and primary-secondary potential formulation....

The controlled-source electromagnetic (CSEM) forward modeling with vector and scalar potentials could provide insights into the inductive galvanic effects. We have developed a finite-element (FE) algorithm for CSEM potentials. first-order nodal shape functions are used potentials, respectively. To mitigate null space thus nonuniqueness of caused by curl operator, we introduce new preconditioner constructed from an incomplete Cholesky decomposition zero fill-ins Laplacian approximation to...

The static shift caused by near-surface conductors poses a significant challenge in magnetotelluric (MT) inversion. We present technique to remove the shifts MT data using equivalent source technique. This method is based on assumption that all are measured or above surface. Since across multiple stations at same frequency general uncorrelated, they can be identified and removed constructing an layer reproduces only coherent signal observed stations. Here we use synthetic three-dimensional...

Magnetotelluric (MT) and magnetovariational (MV) sounding are two principal geophysical methods used to determine the electrical structure of earth using natural electromagnetic signals. The complex relationship between alternating fields can be defined by transfer functions, their proper selection is crucial in a 3-D inversion. A synthetic case was studied assess capacity these functions recover resistivity distribution subsurface evaluate advantages disadvantages tipper vector W complement...

We present an accelerated finite element modeling algorithm for calculating controlled-source electromagnetic (CSEM) responses of a 3D conductivity earth model. A secondary-field formulation is used to model the anomalous field based on predetermined background The inner-boundary condition handled with edge implementation. To accelerate iterative process solving resulting linear system equations, we propose use divergence correction technique. verified using horizontal three-layered and...

We present an element-free Galerkin method (EFGM) based on hybrid background cells for 2.5D direct current (DC) resistivity modelling. In our method, we only need nodal data, which makes it flexible the description of arbitrary complex geoelectric models and efficient local refinement. EFGM, quadrature is calculated with aid cells. The are generated adaptively automatically according to distribution using adaptive cell generation approach, proposed by authors. This approach decreases...