Using Multi-Azimuth Walkaway VSP Data to Image a Tight Gas Bearing Permo-Carboniferous Glaciogenic Reservoir

Abstract

Saudi Aramco has recently acquired multi-azimuth walkaway vertical seismic profile (VSP) data to image the lateral extent and orientation of a tight gas bearing glaciogenic body. Two wells were drilled along a northwest-southeastern trending line approximately 1000 meters apart. The first well was intended to drill through a Permian aged aeolian reservoir; however, the target zone did not show adequate reservoir properties. The second well, in contrast, encountered a thick, tight gas bearing Permo-Carboniferous glaciogenic reservoir. Both zero-offset and multi-offset VSP data were then acquired for delineating the reservoir between two wells. A further goal of the VSP survey was to provide relevant seismic parameters, such as attenuation (Q) and anisotropy parameters (ε and δ), for better reprocessing of 3D surface seismic data that accounts for multiple discrimination, anisotropic velocity analysis and resolution enhancement. Three high quality, multi-azimuth walkaway VSP surveys were acquired at the second well and pre-processed with: (1) geometry definition, (2) multi-component data preconditioning, (3) first break picking, (4) wavefield rotation and separation and (5) surface consistent amplitude compensation. The VTI anisotropy parameters (ε and δ) were estimated using the phase-slowness method for the walkaway VSP data. Both P-wave attenuation and internal-bed multiples were also analyzed using the zero-offset VSP data. Finally, both CDP transformation and pre-stack Kirchhoff depth migration were applied for both isotropic and anisotropic velocity models, to obtain structure images as well as angle gathers for inversion. Results of the 3D surface seismic volume obtained earlier were compared with this study, where previously unclear buried valley geometries, due to limited resolution and multiples contamination, became more interpretable with the VSP imaging. This was further demonstrated with the pre-stack inversion of VSP angle gathers for elastic properties of the glaciogenic reservoir.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015