Permeability Multiplier Prediction using 3D OBC Seismic Data

This work describes an approach in characterizing fractured reservoir of upper Jurassic Carbonate using seismic azimuthal anisotropy. The ultimate objective of this study was to attempt to map permeability multiplier inter-well for the contribution to the simulation model and the subsequent development plan of an oil field offshore Abu Dhabi. The azimuthal seismic anisotropy for fracture prediction method showed fractures that are similar to those indicated by well methods and therefore seismic can be used to detect natural fractures between wells. The confidence in the seismic fracture prediction method’s ability to capture information about fracture in Carbonate reservoir has increased if the well data are accurately integrated. The study interval exists in the dense zone of the Upper Jurassic reservoir with total thickness of 120’. The fractures evidence have been compiled from well data, such as Core, FMI, orthogonal shear sonic, production test, multi-arm caliber….etc. Present day stress is captured from induced fractures direction, borehole breakout, offset field stress map, Eocene structure map and world stress map. All compiled information’s indicated maximum horizontal stress of N10°-30°E direction. The four sectored wide azimuth seismic data set have been fitted to an ellipse to find out the fast and slow velocity direction and the difference between those velocities. The Interval Velocity is sensitive to Lithology, porosity, pore fill; the Vint-Slow is sensitive to the minimum horizontal stress. The lower the VINTslow, the less the minimum horizontal stress, which allows the fracture apertures to be more open. It is observed that the seismic anisotropy map for fractures showed a dominated direction (NNE-SSW) that match with present day stress field. The azimuthal Vint records current day stress field, not paleo-stress field. Good correlation between well permeability multiplier and the fractures map, particularly at the two reference wells. Following the analysis of the azimuthal seismic anisotropy maps such as azimuthal amplitude and interval velocity, a good correlation has been observed between the seismic anisotropy components and the production well test. The two seismic anisotropy components that showed a great deal of link with the computed well permeability multiplier are the computed slow interval velocity and the anisotropy azimuth deviation from the known present day stress. Therefore, the following equation has been written to invert those azimuthal seismic components into permeability multiplier. The resulted map showed match at both input wells and one blind well. Perm. Mult. = ( X * Vint Fast-Slow ) + ( Y / Vint Slow ) + COS (Ref. AZ – Seis. AZ)