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Collaborating Authors
2004 SEG Annual Meeting
Some Practical Issues Related to Migration In the Angle Domain
Lipari, Vincenzo (Politecnico di Milano) | Andreoletti, Clara (ENI, E&P Division) | Bernasconi, Giancarlo (Politecnico di Milano) | Bienati, Nicola (ENI, E&P Division) | Drufuca, Giuseppe (Politecnico di Milano) | Cazzola, Luca (ENI, E&P Division)
Two angles describe the illumination dip vector - ฮป: Elevation of the illumination dip vector The benefits of recasting pre-stack depth migration in the - ฯ: Azimuth of the illumination dip vector angle domain are such to suggest its application in industrial Kirchhoff PSDM software. Here we examine Once the scattering angles are fixed, for each depth point, some practical aspects of the implementation in the angle migration consists in the integral over dip angles, i. e. over domain, namely those that mostly impact performances and the unit ray hemisphere. This is the most natural domain for effectiveness: memory requirements, poor illumination and this integration.
ABSTRACT The azimuthally varying nonhyperbolic moveout of P- waves in orthorhombic media can provide valuable information for characterization of fractured reservoirs and seismic processing. Here, we present a technique to invert long-spread, wide-azimuth P-wave data for the orientation of the vertical symmetry planes and five key moveout parameters โ the symmetry-plane NMO velocities and and the anellipticity parameters ?(1), ? (2), and ?(3). The inversion algorithm is based on a 3D semblance operator applied to the full range of offsets and azimuths using a generalized version of the Alkhalifah-Tsvankin nonhyperbolic moveout equation. Numerical tests on noise-contaminated data show that the inversion yields satisfactory results if the offset-to-depth ratio reaches at least 2.5. The algorithm was successfully tested on wide-azimuth P-wave reflections recorded at Weyburn Field in Canada. Taking azimuthal anisotropy into account increased the semblance values for most long-offset reflection events in the overburden, which indicates that fracturing is not limited to the reservoir level. The estimated symmetry-plane directions are close to the azimuths of the off-trend fracture sets determined from borehole data and shear-wave splitting analysis. The effective moveout parameters estimated by our algorithm also provide input for P-wave time imaging and geometrical-spreading correction in layered orthorhombic media.
- 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...)
Anisotropic PSDM: A Case Study From Western Offshore, India
PSingh, S. (GEOPIC, Oil & Natural Gas Corporation Ltd.) | Sareen, D. (GEOPIC, Oil & Natural Gas Corporation Ltd.) | Pande, K.K. (GEOPIC, Oil & Natural Gas Corporation Ltd.) | Niyogi, K. (GEOPIC, Oil & Natural Gas Corporation Ltd.) | Mehta, C.H. (GEOPIC, Oil & Natural Gas Corporation Ltd.)
ABSTRACT Isotropic pre-stack depth migration (PSDM) in the presence of anisotropy in the subsurface, suffers from positioning errors; vertical as well as lateral. It is well known that layering in shaly formations produces anisotropy which can be modeled as transverse Isotropy (TI). In the present paper we present a case study from shallow offshore India. The subsurface in the area is characterized by massive shale (800โ1000 m) underlain by thick limestone โ shale alternations. The isotropic PSDM showed a 50 m mismatch at this level with hockey-stick effect visible at far offsets on PSDM gathers. We have estimated the heterogeneity and anisotropy parameters i.e., velocity gradient (G), and Thomson parameters (e and d) from seismic and well data. These parameters, estimated in a number of wells spread over 1000 sq. km., were found to be practically constant. These parameters were incorporated in depth velocity modeling and PSDM along 2D profiles. The study of PSDM depth image gathers has shown that in this area non-hyperbolic effect due to heterogeneity dominates beyond offsets of 1140 m (offset-depth ratio of 1.4). The similar effect due to anisotropy is visible only after offsets of 1440 m (offset depth ratio of 1.8). However after Anisotropic PSDM (APSDM) the gathers are flattened up-to 1940 m (offsets depth ratio 2.5). APSDM images match well with well-tops within seismic resolution with accompanying improvements in overall image quality at target horizons.
- Asia > India (1.00)
- North America > United States > Colorado (0.19)
- Geophysics > Seismic Surveying > Seismic Processing (1.00)
- Geophysics > Seismic Surveying > Seismic Modeling > Velocity Modeling (1.00)