Aeromagnetic compensation for the magnetic effects (noise) of the aircraft is now a significant limiting factor in the final data quality. Fundamentally, the residual noise from the aircraft movement after compensation is still 100's of times larger than the signal to noise capabilities of a modern cesium sensor. Users who require highly accurate data for interpretation of subtle features can utilize acquisition systems capable of the required sensitivity and software capable of utilizing the required sensitivity but the final data is flawed by relatively high noise from the aircraft movement effects. Surveys over magnetic terrains face the additional problem that the aircraft attitude required for the compensation techniques are often incorrect. This is due to the measurement of the aircraft attitude via the use of a vector fluxgate magnetometer and the assumption that the Earth's field is uniform. This problem is envisaged to increase as surveying heights get lower and lower, increasing the anomalous magnetic field sensed by both the vector fluxgate and the airborne magnetometer. Non-magnetic orientation devices, such as the use of three GPS receivers on the aircraft are an obvious solution to this problem. The results of this work demonstrates that it is possible to use three well spaced GPS receivers on an aircraft to measure the aircraft attitude to the precision required to compensate for the aircraft effects. The experiments with the different highpass filters used on the data and with the different solvers indicate that with the proper selection of filters and solvers, better compensation results can be obtained.
Lu, Richard S. (ExxonMobil Upstream Research Company) | Lovell, Richard W. (ExxonMobil Development Company) | Dawson, D. Cas (ExxonMobil Development Company) | Yu, Yang (ExxonMobil Upstream Research Company)
The amplitude and frequency loss caused by attenuation through the gas cap of a reservoir (Res A) in offshore west Africa has been recovered using viscoacoustic wave-equation migration (Q-migration) that enhances the seismic resolution beneath the gas cap. Amplitude and frequency attributes below the gas cap match those outside of the gas gap in the Q-migrated volumes. The Q-migration results are being used for well planning and to create a geologic model for reservoir characterization and simulation.
This paper addresses the effects of electrical anisotropy toward the 3D inversion of single-well induction logging data, when anisotropy is not considered. Of concern are possible artifacts that may lead to an incorrect interpretation of the formation about the borehole. Comparison is made of 3D isotropic inversion on a suite of model data, with and without anisotropy, consisting of an infinite layer and layer terminated at the borehole. In both cases, the layer dip (or well deviation) is varied. Inversion of the anisotropic data resulted in an overestimate of the layer conductivity, and the lateral extent of the layer to be confined about the borehole.
Todorovic-Marinic, Dragana (Veritas DGC) | Larson, Glenn (Devon Canada Corp.) | Gray, David (Veritas DGC) | Soule, Greg (Devon Canada Corp.) | Zheng, Ye (Veritas DGC) | Pelletier, Jean (Devon Canada Corp.)
This paper summarizes recent progress towards the goal of identifying productive vertically aligned fractures, cracks or micro-cracks in gas reservoirs using surface seismic data. Our results demonstrate that identification and interpretation of fracture trends can be more accurate by exploiting a new seismic attribute, the envelope of the anisotropic gradient, in an integrated interpretation approach. The method was applied to the Narraway gas field located on the leading edge of the Foothills Disturbed Belt in Northwest Alberta, where intersecting the fracture trends with the borehole is key to achieving a commercial well. The data are analysed to test for a relationship between the fracture density and orientation as indicated by the attribute and the actual well performance, core and logs. Commercial wells were drilled based on the results of this work, thereby validating the applied methodology.
A new analytical solution for acoustic wave propagation in a borehole with an eccentric mandrel is used to compute wavenumbers and excitation vectors for several guided modes as a function of tool position. Parameters used in the examples are relevant for slow shear wave logging-while-drilling applications where a large steel mandrel is free to move laterally about the borehole during data acquisition. An interesting mode splitting phenomenon is featured.
This paper describes a passive seismic imaging case study to track gas movement during CO
3-D migration deconvolution (MD) was successfully applied to prestack migration data in both the time and depth domain. Test results show that migration deconvolution yields improvement in migration image quality by increasing spatial resolution and correcting for irregular illumination. In some results of MD images, new fault pathways are revealed clearly. There is, typically, better resolution improvement at shallow depths than at deeper horizons. This is to be expected from the resolution limits imposed by Fresnel zone physics.
The first phase of a U.S. Department of Energy (DOE) — funded project has been successfully completed (GeoSpectrum, Inc. 2003). Reservoir fractures are predicted using multiple azimuth
The focal transformation is introduced as a promising tool in seismic processing, allowing the incorporation of macro information about the involved wavefields. Application of the focal transform introduces a new domain, the focal domain, that enables the user to separate signal from noise. Applications of particular interest are removing shot-generated noise, interpolation of missing offsets and reconstructing signal beyond aliasing. The latter can be seen as the removal of “aliasing noise”.