Seismic anisotropy parametrization has a vital role in seismic imaging as well as in geomechanical applications. The most common form of seismic anisotropy is Transversely Isotropic (TI) caused by fine geological layering such as in shales. TI, if not incorporated can lead to geological miss-positioning of the seismic image. Walkaway VSP data was used to estimate TI parameters for the Nahr Umr shale, which is a highly anisotropic formation and is a regional cap rock.

Walkaway VSP was recorded using 16 level 3 Component (3C) downhole receiver array positioned across Nahr Umr formation with 402 surface shot points in an offshore field Abu Dhabi. Walkaway VSP provides direct information of upgoing and downgoing primary and shear waves. 3C data was oriented followed by 3C wavefield separation in order to obtain slowness and polarization of the upgoing and downgoing primary and shear waves. Slowness and polarization information gives insight to in situ wavefield propagation.

Slowness and polarization data was inverted to obtain TI anisotropy parameters along receiver array. The inversion of slowness and polarization data does not rely on overburden structural complexities hence providing robust local anisotropy estimates. Strong primary to shear wave mode conversion in the vicinity of Nahr Umr formation helped to obtain good results. The estimated TI anisotropy parameters helped to guide anisotropy parameters in Nahr Umr shale for a nearby field pre-stack depth imaging project (Waqas et al., 2016). The overburden anisotropy needs to be as accurate as possible in order to obtain better seismic imaging and characterization for underlying reservoir. The parameters can also be used in geomechanical applications.

This paper provides TI anisotropy parameters estimation for the regional highly anisotropic shale formation. The unique method was proposed for quite some time in the literature however has not been applied or reported to estimate anisotropy for the Nahr Umr shale.

You can access this article if you purchase or spend a download.