Papers by Michael Zhdanov
This paper presents a parallelized version of the edge-based finite element method with a novel p... more This paper presents a parallelized version of the edge-based finite element method with a novel post-processing approach for numerical modeling of an electromagnetic field in complex media. The method uses an unstructured tetrahedral mesh which can reduce the number of degrees of freedom significantly. The linear system of finite element equations is solved using parallel direct solvers which are robust for ill-conditioned systems and efficient for multiple source electromagnetic (EM) modeling. We also introduce a novel approach to compute the scalar components of the electric field from the tangential components along each edge based on field redatuming. The method can produce a more accurate result as compared to conventional approach. We have applied the developed algorithm to compute the EM response for a typical 3D anisotropic geoelectrical model of the off-shore HC reservoir with complex seafloor bathymetry. The numerical study demonstrates that the modeling algorithm is capable of simulating the complex topography and bathymetry that is commonly encountered in controlled source electromagnetic problems.
pre-printThe direct current and electromagnetic methods have been around for almost 180 years and... more pre-printThe direct current and electromagnetic methods have been around for almost 180 years and have been applied successfully in mining, petroleum, geotechnical, engineering, environmental, groundwater, and tectonic studies. Over such a long period of time, it is possible to lose track of who the pioneers were that developed the various techniques in current use and who wrote the seminal papers on these techniques. As such, a historical review paper is most welcome and, in the past, there were only few attempts to undertake this task (e.g., Rust, 1938; Ward, 1980; Fountain, 1998)
First International Meeting for Applied Geoscience & Energy Expanded Abstracts, 2021
Geophysical studies for offshore exploration have long been dominated by seismic methods. With th... more Geophysical studies for offshore exploration have long been dominated by seismic methods. With the frontier areas of hydrocarbon exploration moving to more challenging geological settings, decisions based on seismic methods alone could be risky. Independent information from alternative geophysical methods integrated with seismic data becomes essential and necessary in this challenging situation. We consider an approach of integrating the complementary information of different geophysical methods to obtain self-consistent geophysical models based on using joint focusing stabilizers in regularized joint inversion of multiphysics data. The method enforces strong coupling between different models and promotes the sharp boundaries of the targets. The practical effectiveness of the developed methods is demonstrated by the case study of integrating and imaging electromagnetic (EM) and full tensor gravity gradiometry (FTG) data collected in the Nordkapp Basin in Barents Sea, Norway.
EGM 2007 International Workshop, 2007
Interpretation of potential and electromagnetic (EM) fields observed over 3D geological structure... more Interpretation of potential and electromagnetic (EM) fields observed over 3D geological structures remains one of the most challenging problems of exploration geophysics. In this paper I present an overview of modern methods of inversion and imaging of gravity, magnetic, and EM data, which are based on new advances in regularization theory related to application of special stabilizing functionals that allow construction of both smooth images of the underground geological structures and models with sharp geological boundaries. I demonstrate that sharp boundary geophysical inversion can improve the efficiency and resolution of the inverse problem solution. I also present a new technique for resolution analysis of regularized geophysical inversion, which evaluates the spatial distribution of the upper bounds of the inverse model errors. These upper bounds of the model variations determine the actual resolution of geophysical inversion. The methods are illustrated with synthetic and practical examples of 3D inversion of potential and EM field's data.
IEEE Geoscience and Remote Sensing Letters, 2020
Towed streamer electromagnetic (TSEM) survey is an efficient data acquisition technique capable o... more Towed streamer electromagnetic (TSEM) survey is an efficient data acquisition technique capable of collecting a large volume of electromagnetic (EM) data over extensive areas rapidly and economically. The TSEM survey is capable of detecting and characterizing marine hydrocarbon (HC) reservoirs. However, interpretation of the TSEM data is still a very challenging problem. We propose solving this problem by migrating the optimal synthetic aperture (OSA) data for the TSEM survey. We first represent the OSA data as a solution of Lippmann-Schwinger equation and then demonstrate that the migration of OSA data is just the inner product of the backwardpropagated and forward-propagated EM fields. The migration problem is solved iteratively within the general framework of the reweighted, regularized, conjugate gradient (RRCG) method. The proposed method was tested with two synthetic models. We also applied this method to the TSEM data set collected in the Barents Sea and revealed a resistive layer at a depth of about 500 m.
SEG Technical Program Expanded Abstracts 2018, 2018
The joint inversion of multiple geophysical datasets can produce more reliable models than the in... more The joint inversion of multiple geophysical datasets can produce more reliable models than the inversion of a single dataset; however, the implementation of the joint inversion can be challenging. There are two main approaches -the petrophysical approach and the structural approach. We detail both approaches based on a simultaneous joint inversion algorithm using the integral equation method coupled with a regularized conjugate gradient inversion. The development presented here is based on the use of Gramian constraints in a joint parametric functional to enforce structural similarity between jointly inverted density and resistivity models using either a direct correlation of the model parameters or a correlation of the gradients of the models. We demonstrate the effectiveness of the developed method and algorithm with two synthetic model studies and a case study of the joint inversion of gravity and magnetotelluric (MT) data acquired over Yellowstone National Park.
SEG Technical Program Expanded Abstracts 2009, 2009
The renewed interest in the methods of electromagnetic field decomposition into upgoing and downg... more The renewed interest in the methods of electromagnetic field decomposition into upgoing and downgoing parts is generated by the practical problem of removing the effect of EM airwaves on marine controlled source electromagnetic data collected in shallow water. In this paper we consider the principles of solving this problem using the classical methods of EM field separation into external and internal parts. We demonstrate that the most general approach to upgoing/downgoing field decomposition is based on the theory of Stratton-Chu type integrals. This approach allows us to separate the field observed on an arbitrary surface. In the case of flat observational surface, the Stratton-Chu method is equivalent to the decomposition technique based on the Fourier transform in the spatial frequency domain. We present also a novel method of EM field separation using the method of horizontal gradients of the EM field. The new technique is tested on synthetic MCSEM data. We demonstrate also that the method represents a useful tool for a rapid qualitative interpretation of MCSEM data.
SEG Technical Program Expanded Abstracts 2016, 2016
3D inversion of airborne electromagnetic data is a challenging task due to the large amounts of d... more 3D inversion of airborne electromagnetic data is a challenging task due to the large amounts of data collected over relatively large areas. In this paper we detail an inversion algorithm based on a moving sensitivity domain approach using the integral equation method coupled with a multistep regularized conjugate gradient inversion. To tackle the computational demands, along with the reduction of the problem due to the moving sensitivity domain approach, we also parallelize the problem over the data using Message Passing Interface (MPI) and OpenMP. The workflow of the interpretation includes 1D inversion to obtain a background structure that serves as an input to the 3D inversion. The background is either a half-space, unique under each data point, in the case of frequency domain, or layered background in the case of time domain inversion. We demonstrate the effectiveness of the developed method and computer software by 3D inversion examples of frequency and time domain airborne EM surveys.
SEG Technical Program Expanded Abstracts 2013, 2013
Marine controlled source electromagnetic (MCSEM) surveys have become an important part of offshor... more Marine controlled source electromagnetic (MCSEM) surveys have become an important part of offshore petroleum exploration. However, there exist very nearshore areas, with the depth varying from tens of meters to a few hundred meters, where it is technically difficult to use a towed electrical bipole transmitter. In some cases, the operating of the controlled electric sources in the nearshore zones is prohibited by the environmental concerns of the impact of the powerful electric current on the marine fauna. To address the needs of EM exploration in the nearshore zones, a new marine EM method has been recently developed, which is called marine electromagnetic remote sensing (MEMRS). This method consists of a very high moment onshore electric bipole transmitter and a large array of offshore receivers. In this paper we present a feasibility study of the MEMRS method.
Minerals, 2018
Recent developments in large-scale geophysical inversions made it possible to invert the results ... more Recent developments in large-scale geophysical inversions made it possible to invert the results of entire airborne geophysical surveys over large areas into 3D models of the subsurface. This paper presents the methods for and results of the interpretation of the data acquired by a multiphysics airborne geophysical survey in Saudi Arabia. The project involved the acquisition, processing, and interpretation of airborne electromagnetic, gravity, and magnetic geophysical data over an 8000 square kilometer area. All the collected data were carefully analyzed and inverted in 3D models of the corresponding physical properties of the subsurface, including 3D density, magnetization vector, and conductivity models. This paper summarizes the interpretation of all geophysical data sets collected during the field airborne survey. The goal of the paper is to demonstrate how the advanced 3D modeling and inversion methods can be effectively used for interpretation of multiphysics airborne survey data and to study and analyze the potential of the survey area for natural resource exploration in Saudi Arabia.
IEEE Geoscience and Remote Sensing Letters, 2015
Modeling of induced polarization (IP) phenomena is important for developing effective methods for... more Modeling of induced polarization (IP) phenomena is important for developing effective methods for remote sensing of subsurface geology. However, the quantitative interpretation of IP data in a complex 3-D environment is still a challenging problem of applied geophysics. This letter develops a method of determining a 3-D distribution of the four parameters of the Cole-Cole model based on surface IP data. The method takes into account the nonlinear nature of both electromagnetic induction and IP phenomena. The solution of the 3-D IP inverse problem is based on the regularized conjugate gradient method. The method was tested on a synthetic model with variable dc conductivity, intrinsic chargeability, time constant, and relaxation parameters, and it was also applied to the actual 3-D IP survey data. We demonstrate that the four parameters of the Cole-Cole model, namely, dc electrical resistivity, chargeability, time constant, and the relaxation parameter, can be recovered from the observed IP data simultaneously.
SEG Technical Program Expanded Abstracts 2014, 2014
This paper introduces a novel approach to the optimal design of the synthetic aperture method for... more This paper introduces a novel approach to the optimal design of the synthetic aperture method for marine controlled source electromagnetic (MCSEM) surveys. We demonstrate that the sensitivity of the MCSEM survey to a specific geological target could be enhanced by selecting the appropriate amplitude and phase coefficients of the corresponding synthetic aperture. We have developed a general optimization technique to find the optimal parameters of the synthetic aperture method. This approach makes it possible to increase the corresponding ratio between total and background fields within the area of an expected reservoir anomaly and in this way improve the resolution of the EM data with respect to potential subsurface targets. We also demonstrate that this optimal synthetic aperture method can be used for a removal of the distorting airwave effect from the MCSEM data collected in shallow water.
SEG Technical Program Expanded Abstracts 2006, 2006
A new approach to EM forward modeling from the grain-scale to deposit-scale is presented using a ... more A new approach to EM forward modeling from the grain-scale to deposit-scale is presented using a porphyry copper system. The Generalized Effective Medium Theory of the induced polarization (GEMTIP) effect and electromagnetic (EM) field propagation in heterogenous polarizable media presented by allows the incorporation of rock-scale parameters such as mineralization and/or fluid content, matrix composition, porosity, anisotropy, and the polarizability of the formations. GEMTIP is used for rock-scale forward modeling from grain-scale parameters. Empirical data from rock-scale measurements are in good agreement with GEMTIP forward modeling output for pyrite and chalcopyrite bearing rocks. To further our understanding of IP on a larger scale, deposit-scale modeling is conducted for a porphyry system. A simplified porphyry model is created for future detectability and mineral discrimination studies.
SEG Technical Program Expanded Abstracts 2017, 2017
The Synthetic Aperture (SA) method is one of the key techniques in remote sensing using radio fre... more The Synthetic Aperture (SA) method is one of the key techniques in remote sensing using radio frequency signals. During recent years this method has also been applied to low frequency electromagnetic (EM) fields used for geophysical exploration. This paper demonstrates that the concept of the SA EM method can be extended to rapid imaging of large volumes of towed streamer EM data. We introduce a notion of virtual receivers, which complement the actual receivers in the construction of the SA for the towed streamer data. The method is illustrated by imaging of towed streamer EM data acquired in the Barents Sea. Remarkably, imaging the entire towed streamer EM survey requires just a few seconds of computation time on a desktop PC. This result is significant because it opens a possibility for real-time imaging of towed streamer EM survey data.
SEG Technical Program Expanded Abstracts 2010, 2010
We present a new formulation of the hybrid method for threedimensional (3D) electromagnetic (EM) ... more We present a new formulation of the hybrid method for threedimensional (3D) electromagnetic (EM) modeling in complex structures with inhomogeneous background conductivity (IBC). This method overcomes the standard limitation of the conventional IE method related to the use of a horizontally layered background only. The new method allows us to compute the effect of IBC structures by using any appropriate numerical method which may be able to build a model with a flexible grid. This approach seems to be extremely useful in computing EM data for multiple geologic models with some common geoelectrical features, like terrain, bathymetry, or other known structures. It may find wide application in inverse problem solution, where we have to keep some known geologic structures unchanged during the iterative inversion. The method was carefully tested for modeling the EM field for complex structures with known variable background conductivity. The effectiveness of this approach is illustrated by modeling marine magnetotelluric (MT) data.
SEG Technical Program Expanded Abstracts 2016, 2016
Marine towed streamer electromagnetic (EM) surveys have become extensively used for offshore hydr... more Marine towed streamer electromagnetic (EM) surveys have become extensively used for offshore hydrocarbon (HC) exploration. The mainstream approach to interpretation of towed streamer EM data is based on 2.5D and/or 3D inversions of the observed data into the resistivity models of the sea-bottom formations. However, in the case of a reconnaissance towed streamer EM survey with the goal of scanning a vast area of the marine shelf, one needs to use a rapid imaging technique, which could provide a real-time evaluation of the potential prospects. This paper introduces an innovative technique of rapid imaging of towed streamer EM data based on the concept of the synthetic aperture method. We introduce an optimization technique to find the optimal parameters of the synthetic aperture method for a towed streamer EM survey, and demonstrate that this method increases the EM response from the potential seabottom targets effectively. Towed streamer EM data acquired over the Troll oil and gas fields in the North Sea are used as a test study. Our imaging results are shown to be consistent with those obtained by rigorous inversion and with the true location of the HC deposits.
SEG Technical Program Expanded Abstracts 2016, 2016
In this paper we introduce a large-scale 3D inversion technique for towed streamer electromagneti... more In this paper we introduce a large-scale 3D inversion technique for towed streamer electromagnetic (EM) data, which incorporates seismic constraints. The inversion algorithm is based on the integral equation (IE) forward modeling and utilizes a re-weighted regularized conjugate gradient method with adaptive regularization to minimize the objective functional. We have also incorporated in the inversion the moving sensitivity domain approach in order to invert the entire large-scale towed streamer EM survey data while keeping the accuracy and reducing the time and memory/storage of the computation. The developed algorithm and software can take into account the constraints based on seismic and well-log data, and provide the inversion guided by these constraints. Application of the developed method to the interpretation of the largescale towed streamer EM survey data acquired in the Barents Sea demonstrates its practical effectiveness.
SEG Technical Program Expanded Abstracts 2014, 2014
This paper introduces an approach to 3D modeling and inversion of the airborne electromagnetics (... more This paper introduces an approach to 3D modeling and inversion of the airborne electromagnetics (AEM) that is suited to arbitrarily complex earth models with very high conductivity contrasts and rugged topography, yet is fast enough to consider large surveys. We use a hybrid FE-IE method, which directly avoids errors associated with numerical differentiation and interpolation of the electric vector potentials at the edges of the elements containing the receiver. This approach is stable and accurate and for conductivity contrasts in excess of 10⁸:1, as is typically required for practical AEM interpretation. We incorporate the moving sensitivity domain method into this modeling framework to increase the modeling speed for an entire survey by several orders of magnitude. A case study for the 3D inversion of 90 line km of DIGHEM data from the Reid-Mahaffy test site is presented to demonstrate the efficacy of our method.
SEG Technical Program Expanded Abstracts 2006, 2006
We apply a new formulation of the integral equation (IE) method with inhomogeneous background con... more We apply a new formulation of the integral equation (IE) method with inhomogeneous background conductivity (IBC) for modeling marine controlled source electromagnetic (MCSEM) data in areas with significant bathymetric inhomogeneities. We also introduce an approach for accuracy control of the IBC IE method. This new approach provides us with the ability to improve the accuracy of computations by applying the IBC technique iteratively. This approach seems to be extremely useful in computing EM data for multiple geological models with some common geoelectrical features, like terrain, bathymetry, or other known structures. It may find wide application in inverse problem solution, where we have to keep some known geological structures unchanged during the iterative inversion. The effectiveness of this approach is illustrated by modeling marine controlled source electromagnetic (MCSEM) data in model with significant bathymetric inhomogeneities.
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Papers by Michael Zhdanov