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Collaborating Authors
TechnoImaging
Summary The distortion of regional electric fields by local structures represents one of the major problems facing three-dimensional magnetotelluric (MT) interpretation. The effect of 3D local inhomogeneities on MT data can be described by a distortion matrix. In this paper, we develop a method for simultaneous inversion of the full MT impedance data for 3D conductivity distribution and for a distortion matrix with complex components. We use integral equations method for forward modeling. Tikhonov regularization is employed to solve the resulting inverse problem. Minimization of the parametric functional is achieved via a conjugate gradient method. The inversion algorithm was tested on the synthetic data from Dublin Secret Model II (DSM 2), for which multiple inversion solutions are available for comparison. We also investigate a possibility of using the developed approach for corrections to the effect of topography on the MT data. Finally, the results are presented of an application of the inversion to a regional MT dataset acquired as part of the EarthScope project over the Great Basin region of the Western United States. Introduction Distortion of regional MT responses by local structures is one of the challenges in the interpretation of MT data. Due to the computing limitations it is difficult to model local 3D structures to a small enough scale. There are several approaches available for minimizing static shift effects. For example, one can use additional data produced by the controlled source EM surveys, e.g., coincident time-domain EM soundings (Pellerin and Hohmann, 1990). Torres-Verdin and Bostick (1992) proposed the EMAP technique of deploying electric dipoles along a continuous survey path to reduce the static shift effect in the data. In the paper by deGroot-Hedlin (1991), the unknown static shift was included as a parameter of the inversion. The 3D MT inversion algorithm of Sasaki and Meju (2006) took into account the static shift of the impedance amplitudes but not amplitude or phase mixing. Zhdanov et. al. (2011) normalized observed MT impedances by their amplitudes in order to remove the major part of the static shift effect from the amplitude data, considering that the phase of impedances is less affected by near-surface inhomogeneities. Patro et al. (2013) presented an inversion algorithm for the MT phase tensor, which was based on a similar assumption of the lesser influence of near-surface distortions on the phase data.
- North America > United States > Idaho (0.50)
- North America > United States > Utah (0.36)
- North America > United States > Nevada (0.36)
- (3 more...)
- North America > United States > Wyoming > Great Basin (0.99)
- North America > United States > Utah > Great Basin (0.99)
- North America > United States > Oregon > Great Basin (0.99)
- (5 more...)
Summary One of the major problems in the modeling and inversion of marine controlled source electromagnetic (MCSEM) data is related to the need for accurate representation of very complex geoelectrical models typical for marine environment. At the same time, the corresponding forward modeling algorithms should be powerful and fast enough to be suitable for repeated use in hundreds of iterations of the inversion and for multiple transmitter/receiver positions. To this end, we have developed a novel 3D modeling and inversion approach, which combines the advantages of the finite difference (FD) and integral equation (IE) methods. In the framework of this approach, we solve the Maxwell’s equations for anomalous electric fields using the FD approximation on a staggered grid. Once the unknown electric fields in the computation domain of the FD method are computed, the electric and magnetic fields at the receivers are calculated using the IE method with the corresponding Green’s tensor for the background conductivity model. This approach makes it possible to compute the fields at the receivers accurately without the need of very fine FD discretization in the vicinity of the receivers and without the need for numerical differentiation and interpolation. We have also developed an algorithm for 3D inversion of MCSEM data based on the hybrid FD-IE method. A model study for the 3D inversion of MCSEM data is presented to demonstrate the effectiveness of the developed hybrid method. Introduction The IE method represents one of the most effective numerical solvers for localized anomalous structures embedded in a layered earth. One of the advantages of the IE method is that it only requires a solution within the anomalous domain, and the electric and magnetic fields at the receivers are calculated based on the Green’s tensor approach. The IE modeling domain includes inhomogeneous geoelectrical structures only and it is typically very small compared to the modeling domains of the differential equation (DE) methods, which require a large computational domain to satisfy to the corresponding boundary conditions. At the same time, the system matrix of the IE method is dense, so if the complexity of the model grows, the IE method requires significantly larger amount of computational memory and time.
The towed streamer EM system makes it possible to collect EM data with a high production rate and over very large survey areas. At the same time, 3D inversion of the towed streamer EM data remains a very challenging problem because of the huge number of transmitter positions of the moving towed streamer EM system, and, correspondingly, the huge number of forward and inverse problems needed to be solved for every transmitter position over the large areas of the survey. We overcome this problem by exploiting the fact that a towed streamer EM system's sensitivity domain is significantly smaller than the area of the towed streamer EM survey. We apply the concept of moving sensitivity domain, originally developed for airborne EM surveys, to the interpretation of marine EM survey data. This makes it possible to invert the entire towed streamer EM surveys with no approximations into high-resolution 3D geoelectrical sea-bottom models. Our implementation is based on the 3D integral equation (IE) method for computing the responses and Fréchet derivatives for 3D anisotropic geoelectrical models. In the framework of the concept of the moving sensitivity domain, for a given transmitter-receiver pair, the EM responses and Fréchet derivatives are computed from a 3D Earth model that encapsulates the towed EM system's sensitivity domain. The Fréchet matrix for the entire 3D Earth model is then constructed as the superposition of Fréchet derivatives from all transmitter-receiver pairs over the entire 3D earth model. This makes large-scale 3D inversion a tractable problem with moderate cluster resources. We present case studies of 3D anisotropic inversion of towed streamer EM data from the Troll West Oil Province and Mariner field in the North Sea.
- North America > United States (1.00)
- Europe > United Kingdom > North Sea (0.73)
- Europe > Norway > North Sea > Northern North Sea (0.16)
- Europe > United Kingdom > North Sea > Northern North Sea > East Shetland Basin > Block 9/11b > Mariner Field > Maureen Formation (0.99)
- Europe > United Kingdom > North Sea > Northern North Sea > East Shetland Basin > Block 9/11b > Mariner Field > Heimdal Formation (0.99)
- Europe > United Kingdom > North Sea > Northern North Sea > East Shetland Basin > Block 9/11a > Mariner Field > Maureen Formation (0.99)
- (17 more...)
3D Inversion of Borehole to Surface Electromagnetic Data in a Multiple Reservoirs Survey
Marsala, Alberto F. (Saudi Aramco) | Zhdanov, Michael S. (TechnoImaging) | Endo, Masashi (University of Utah) | Black, Noel (TechnoImaging)
Summary There is a growing interest in developing innovative geophysical methods for monitoring hydrocarbon reservoirs. One emerging technique is based on using the borehole electric current transmitter and a grid of surface electric field receivers for detailed mapping of the subsurface resistivity of oil- and gas-producing fields. This method is often called Borehole to Surface Electromagnetic (BSEM) surveying. We introduce a rigorous method for 3D inversion of BSEM data based on the integral equation approach and adaptive regularization. We have applied our developed method to 3D inversion of a field BSEM dataset collected in a giant oilfield in Saudi Arabia. It was demonstrated that 3D inversion of the BSEM data can be effectively used for mapping and monitoring fluid distribution inside a reservoirs and imaging the oil-water contact.
Summary 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 10:1, 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.
- North America > United States > Texas > Permian Basin > Central Basin > Cox Field (0.89)
- Asia > Turkmenistan > Aspheron Ridge > Cheleken Contract Area > Cheleken Field > Dzhygalybeg Field (0.89)
Anisotropic 3D inversion of towed-streamer electromagnetic data: Case study from the Troll West Oil Province
Zhdanov, Michael S. (University of Utah) | Endo, Masashi (TechnoImaging) | Yoon, Daeung (University of Utah) | Čuma, Martin (University of Utah) | Mattsson, Johan (Petroleum Geo-Services) | Midgley, Jonathan (Petroleum Geo-Services)
Abstract One of the critical problems in the interpretation of marine controlled-source electromagnetic geophysical data is taking into account the anisotropy of the rock formations. We evaluated a 3D anisotropic inversion method based on the integral equation method. We applied this method to the full 3D anisotropic inversion of towed-streamer electromagnetic (EM) data. The towed-streamer EM system makes it possible to collect EM data with a high production rate and over very large survey areas. At the same time, 3D inversion of towed-streamer EM data has become a very challenging problem because of the huge number of transmitter positions of the moving towed-streamer EM system, and, correspondingly, the huge number of forward and inverse problems needed to be solved for every transmitter position over the large areas of the survey. We overcame this problem by exploiting the fact that a towed-streamer EM system’s sensitivity domain is significantly smaller than the area of the towed-streamer EM survey. This approach makes it possible to invert entire towed-streamer EM surveys with no approximations into high-resolution 3D geoelectrical sea-bottom models. We present an actual case study for the 3D anisotropic inversion of towed-streamer EM data from the Troll field in the North Sea.
- Europe > Norway > North Sea > Northern North Sea > North Viking Graben > PL 054 > Block 31/6 > Troll Field > Sognefjord Formation (0.99)
- Europe > Norway > North Sea > Northern North Sea > North Viking Graben > PL 054 > Block 31/6 > Troll Field > Heather Formation (0.99)
- Europe > Norway > North Sea > Northern North Sea > North Viking Graben > PL 054 > Block 31/6 > Troll Field > Fensfjord Formation (0.99)
- (11 more...)
Joint 3D Inversion of Time- And Frequency-Domain Airborne Electromagnetic Data
Sunwall, David (TechnoImaging) | Cox, Leif (TechnoImaging) | Zhdanov, Michael (University of Utah)
Summary We present a method of 3D joint inversion of frequency-domain and time-domain airborne electromagnetic (AEM) data. The method is based on the concept of a moving sensitivity domain, which makes it possible to invert large scale AEM surveys to 3D conductivity models. Frequency-domain AEM data have better resolution for near-surface structures, while time-domain data can resolve deeper geologic targets. By combining these two methods in joint inversion, we produce well resolved images of an entire geological section under investigation. There are many mature areas in mining and petroleum producing provinces where both frequency-domain and time-domain airborne surveys already exist. Reprocessing these areas with the proposed joint inversion scheme may lead to improved images, better understanding, and a more accurate geologic model.
Feasibility Study of Electromagnetic Monitoring of CO2 Sequestration in Deep Reservoirs
Zhdanov, Michael S. (University of Utah) | Endo, Masashi (TechnoImaging) | Black, Noel (TechnoImaging) | Spangler, Lee (Big Sky Carbon Sequestration Partnership) | Fairweather, Stacey (Big Sky Carbon Sequestration Partnership) | Hibbs, Andrew (GroundMetrics) | Eiskamp, George A. (GroundMetrics) | Will, Robert (Schlumberger Carbon Services)
Summary Geophysical monitoring of carbon dioxide (CO2) injections in a deep reservoir has become an important component of carbon capture and storage (CCS) projects. Until recently, the seismic method was the dominant technique used for reservoir monitoring. In this paper we present a feasibility study of permanent electromagnetic (EM) monitoring of CO2 sequestration in a deep reservoir using a novel borehole-to-surface EM (BSEM) method. The advantage of this method is that the sources of the EM field are located within the borehole close to the target reservoir, which increases the sensitivity and resolution of the method. Another innovation is the use of capacitive electric field sensors with an operational lifetime of tens of years. We illustrate the effectiveness of the BSEM method by computer simulating CO2 injection monitoring in the Kevin Dome sequestration site in Montana, USA.
- North America > United States > Montana (0.70)
- Africa > South Africa > Western Cape Province > Indian Ocean (0.25)
- Oceania > Australia > Western Australia > North West Shelf > Carnarvon Basin > Carnarvon Basin > Dampier Basin > Rankin Platform > Greater Gorgon Development Area > Block WA-268-P > Greater Gorgon Field > Gorgon Field (0.99)
- Oceania > Australia > Western Australia > North West Shelf > Carnarvon Basin > Carnarvon Basin > Carnarvon Basin > Rankin Platform > Greater Gorgon Development Area > Block WA-268-P > Greater Gorgon Field > Gorgon Field (0.99)
- Oceania > Australia > Western Australia > North West Shelf > Carnarvon Basin > Alpha Arch > Dampier Basin > Rankin Platform > Greater Gorgon Development Area > Block WA-268-P > Greater Gorgon Field > Gorgon Field (0.99)
- (7 more...)
Summary Moving sensitivity domain that varies with frequency was implemented and tested in a parallel magnetotelluric (MT) integral equation inversion. This approach reduces computation time and memory requirements. We assess the robustness of the approach by model tests and apply it to the inversion of EarthScope MT data collected over the Northwestern US. Prominent features obtained by this inversion include resistive structure associated with the Juan de Fuca slab subducting beneath the northwestern United States and the conductive zone of partially melted material above the subducting slab corresponding to the Cascade volcanic arc. We also observe extensive areas of moderate-to-high conductive asthenosphere below 100 to 200 km and high-conductive body associated with the Yellowstone mantle plume.
- Geology > Structural Geology > Tectonics > Plate Tectonics (0.90)
- Geology > Geological Subdiscipline > Volcanology (0.87)
- South America > Argentina > Noroeste Basin (0.99)
- North America > United States > Wyoming > Great Basin (0.99)
- North America > United States > Utah > Great Basin (0.99)
- (6 more...)
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)
- Data Science & Engineering Analytics > Information Management and Systems (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Exploration, development, structural geology (0.90)
- Information Technology > Mathematics of Computing (0.63)
- Information Technology > Hardware > Memory (0.34)
Summary The geological interpretation of gravity and gravity gradiometry data is a very challenging problem. 3D inversion represents the only practical tool for the quantitative interpretation of gravity gradiometry data. However, 3D inversion is a complicated and time-consuming procedure that is very dependent on the a priori model and constraints used. 3D migration gives a rapid imaging of a geological target that can be used for interpretation or as an a priori model for subsequent 3D regularized inversion. This method is based on a direct integral transformation of the observed gravity gradients into a subsurface density distribution. Moreover, migration can be applied iteratively to get more accurate subsurface density distribution, and the results are comparable to those obtained from regularized inversion. We present a model study and a case study for the 3D iterative imaging of FTG gravity gradiometry data from Nordkapp Basin, Barents Sea.