3D seismic physical modeling for azimuthal variations of P-wave velocity
Khaled Al Dulaijan, Gary F. Margrave, Joe Wong
Information related to fracture orientation and intensity is vital for the development of unconventional hydrocarbons, such as tight sand gas and shale gas. Numerical modeling provides a valuable tool for geophysicists to test and validate their methodologies that provide them with information about reservoirs. Fractures make numerical modeling more complicated and introduce complexities that might even require geophysicists to validate their numerical models before using them to assess their methods. Alternatively, physical modeling provides a unique opportunity to test, validate, and develop methods for characterizing fractured reservoirs. This report utilizes seismic physical modeling to test a method for Velocity Variations with Azimuth (VVAz) based on the non-hyperbolic NMO equation for TI media that was derived by Grechka and Tsvankin (1998).
A three-layer model was built using vertically laminated Phenolic overlain by Plexiglas to represent a fractured reservoir overlaid by an isotropic overburden. HTI planes of phenolic have an orientation in northern half of the model that is orthogonal to HTI planes in southern half. A third layer of water is added to the model. 3D seismic data is acquired in patches. The data is processed with a surface-consistenst amplitude and deconvolutions, so it can be used for amplitude analysis as well. Third reflector, in the CDP domain, is very weak due to attenuation of anisotropic phenolic and low fold of data. After sectoring the data, orientation and intensity of anisotropy is estimated by VVAz. Results of anisotropy orientation matches the physical model.