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Results
Summary Analyses of crosshole georadar data provide estimates of the electromagnetic velocity and attenuation of the probed media. In contrast to inversions of traveltimes ray-based inversions of amplitudes depend critically on a priori assumptions about the directive properties of the antennas. In particular, the influence of electric material property fluctuations on antenna performance may lead to serious distortions of the radiation pattern. Such distortions cannot be accounted for by currently employed ray-based amplitude inversion algorithms. To explore the problem of antenna coupling to local heterogeneities, we generate synthetic crosshole georadar data for a suite of stochastic models using a finite-difference solution of Maxwell’s equations in cylindrical coordinates. Analyses of the radiation patterns extracted from the synthetic data indicate that distortions of the radiation patterns are primarily due to propagation effects and not to dipole-coupling effects.
Summary The Thomsen anisotropy parameters (Thomsen, 1986) describe the most important aspects of anisotropy on velocity. In the case of anisotropy caused by fine layering effects, the parameters are in fact defined in the long wavelength limit, meaning that it is implicitly assumed that all the fine layering is very fine compared to the dominant seismic wavelength. When this assumption is not met (which is often the case to some degree in practical cases), the Thomsen anisotropy parameters can still be calculated using a moving averaging technique. It will be shown with an example that the anisotropy parameters derived in this way may become strongly dependent on the scale (i.e. related to the size of the averaging window) they are calculated on.
- North America > United States > Utah (0.16)
- Europe > Netherlands (0.16)
Summary This article introduces the new fourth-order implicit time-stepping scheme for the numerical solution of the acoustic wave equation, as a variant of the conventional modified equation method. For an efficient simulation, the scheme incorporates a locally one-dimensional(LOD) procedure having the splitting error ofs(Ñt4) . Its stability and accuracy are compared with those of the standard explicit fourth-order scheme. It has been observed from various experiments for 2d problem that (a) the computational cost of the implicit LOD algorithm is only about 40% higher than that size, (b) the implicit LOD method produces slightly less dispersive solutions in heterogeneous media, and (c) its numerical stability and accuracy match those of the explicit method quite well.
Summary An integrated rock/fluid physics and reservoir modeling process relates changes in fluid pressure and composition to changes in the seismic properties of the reservoir. Through calibration of the model with petrophysical relations, a quantitative interpretation of time-lapse seismic data is made. At Weyburn Field this process is used successfully to track a miscible CO2 flood. In further research, the forward model developed in this work could be extended to joint inversion of production and seismic data. Introduction Weyburn Field is a fractured carbonate reservoir in the Williston Basin, Southern Saskatchewan (Churcher and Edmonds, 1994). The field is large, with 1.4 billion barrels of oil in place and to-date recovery of 24%. To improve oil recovery, a miscible CO2 flood is underway.
- North America > United States (1.00)
- North America > Canada > Saskatchewan (1.00)
- Geophysics > Time-Lapse Surveying > Time-Lapse Seismic Surveying (1.00)
- Geophysics > Seismic Surveying (1.00)
- North America > Canada > Saskatchewan > Williston Basin > Weyburn Field > Mission Canyon Formation (0.99)
- North America > Canada > Saskatchewan > Williston Basin > Weyburn Field > Madison Formation (0.99)
- North America > Canada > Saskatchewan > Williston Basin > Weyburn Field > Forbisher Formation (0.99)
- (3 more...)
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Four-dimensional and four-component seismic (1.00)
- Reservoir Description and Dynamics > Improved and Enhanced Recovery > Chemical flooding methods (1.00)
- Reservoir Description and Dynamics > Formation Evaluation & Management > Seismic (four dimensional) monitoring (1.00)
History Matching of CO2 Flow Models Using Seismic Modeling And Time-lapse Data
Lygren, M. (Schlumberger Stavanger Research) | Halvorsen, K.Å. (Schlumberger Stavanger Research) | Randen, T. (Schlumberger Stavanger Research) | Sønneland, L. (Schlumberger Stavanger Research) | Dahl, G.V. (Schlumberger Stavanger Research) | Lindeberg, E. (SINTEF Petroleum) | Bergmo, P. (SINTEF Petroleum)
Summary A method for discriminating between different reservoir flow models using forward modeling and time-lapse seismic is presented. A rock-physical model is used in order to generate synthetic time-lapse acoustic responses based on flow model predictions. From the acoustic properties a pull-down caused by modifications in acoustic velocity is calculated and compared to real measurements. Full synthetic seismograms are also generated. The method has been applied to the Sleipner CO2 sequestration project where time-lapse seismic is used to monitor the injected gas. Different vertical migration processes of the CO2 may explain the observed time-lapse response. In the present paper the new methodology has been used to discriminate between these processes.
- North America > United States > Utah (0.17)
- Europe > Norway > North Sea (0.15)
- Geophysics > Time-Lapse Surveying > Time-Lapse Seismic Surveying (1.00)
- Geophysics > Seismic Surveying (1.00)
- Europe > Norway > North Sea > Central North Sea > South Viking Graben > PL 046 > Block 15/9 > Sleipner Field > Draupne Formation (0.99)
- Europe > Norway > North Sea > Central North Sea > South Viking Graben > PL 046 > Block 15/8 > Sleipner Field > Draupne Formation (0.99)
- Europe > Norway > North Sea > Central North Sea > South Viking Graben > PL 046 > Block 15/6 > Sleipner Field > Draupne Formation (0.99)
Summary Discriminating linear from non-linear detectable seismic changes during the evolution of a reservoir can be achieved using a combination of time-lapse diagnostic measures. Predictability and spectral coherency are two of those methods, which have recently been utilised to QC time-lapse results during processing. Here, we show that the combination of these two measures and the estimates of amplitude, phase and time misfits, calculated concurrently, allow the separation of linear from non-linear wavefield perturbation changes. It was found that heterogeneous reservoirs result in non-linear wavefield changes in comparison to homogeneous ones which produce linear changes. Introduction Time-lapse seismic has become part of effective reservoir management processes that include reservoir simulation and production history matching. However, measures of analysing the observed difference in the time-lapse seismic data are still specific for the individual reservoir and production case.
- North America > United States > Utah (0.17)
- Europe (0.16)
- Europe > Norway > North Sea > Northern North Sea > North Viking Graben > PL 104 > Block 30/9 > Oseberg Field > Tarbert Formation (0.99)
- Europe > Norway > North Sea > Northern North Sea > North Viking Graben > PL 104 > Block 30/9 > Oseberg Field > Oseberg Formation (0.99)
- Europe > Norway > North Sea > Northern North Sea > North Viking Graben > PL 079 > Block 30/9 > Oseberg Field > Tarbert Formation (0.99)
- (3 more...)
Summary Magnetic data collected over bodies of high susceptibility contain significant self-demagnetization effects. Examples include mineral exploration surveys over banded iron formations and surveys for detection and discrimination of unexploded ordinance. Standard forward modeling methods that neglect the effects of self-demagnetization can produce inaccurate results and subsequent deterioration in performance of the inverse solution. Here we solve the full Maxwell''s equations for electrostatics using a finite volume discretization. This forward modeling forms the foundation for a subsequent inversion algorithm.
- North America > Canada (0.29)
- North America > United States > Utah (0.17)
- Energy > Oil & Gas > Upstream (0.70)
- Materials > Metals & Mining (0.68)
Summary FEMAX is a new software developed for 2D numerical simulation of magnetic induction tools in vertical wewlls. With the simulation the formation is assumed to be horizontally layered, the resistivity most likely anisotropic, and the borehole mud and possible invasions are considered. FEMAX (Finite Element method for Axially symmetric problems) is based upon the finite element Nedéléc discretization of the Maxwell equations and the special-purpose algebraic solver fitted to specific features of the problem.
Summary We develop an inversion methodology for 3D electromagnetic data when the forward model consists of Maxwell''s equations in which the permeability is constant but electrical conductivity can be highly discontinuous. The goal of the inversion is to recover the conductivity given measurements of the electric and/or magnetic fields. A standard Tikhonov regularization is incorporated and we use an inexact, all-at-once methodology (Biros and Ghattas, 2000; Haber and Ascher, 2001b), solving the forward problem and the inverse problem simultaneously in one iterative process. This approach allows development of highly efficient algorithms.
Summary We develop algorithms to forward model and invert magnetometric resistivity (MMR) responses over an arbitrary 3-D conductivity structure. The observed data can be at the surface or in the borehole. In the forward modelling algorithm, the secondorder partial differential equations for the scalar and vector potentials are discretized on a staggered-grid using the finitevolume technique. In the inversion method, we discretize the 3-D model into a large number of rectangular cells of constant conductivity, and the final solution is obtained by minimizing a global objective function composed of the model objective function and data misfit.
- Oceania > Australia (0.29)
- North America > United States > Utah (0.16)