Incorporation of Geology, Wells, Rockphysics into Anisotropy Estimation for Seismic Depth Imaging Enables “True Earth Model”

Bui, Huyen ¹; Ng, Peck Hwa David ¹; Zhou, Jenny ¹; Kue, Chih-Wen ¹; Smith, Martiris ¹
(1) WesternGeco, Shlumberger, Houston, TX.

Subsequent to our previous paper on how to indicate anisotropy from well-seismic mistie analyses (Bui et al, 2010), we continue to present our currently practical workflow of how to incorporate geology, well and rockphysics in anisotropy estimation for seismic depth imaging. As we all know, that the seismic velocity is an important variable that can result in the lateral and vertical mis-positioning of the reservoir targets. Likely, it was always thought that if the depth migrated velocity was wrong, seismic anisotropic functions (Thomsen’s delta and epsilon) were wrong in a vertical transverse isotropic (VTI) case. In fact, the Thomsen’s delta and epsilon functions help to flatten the gathers, but the depth still may be wrong at zero offset. In fact, the most important parameter that results in wrong depth is the vertical seismic velocity used in seismic migration. In order to create the right migrated seismic velocity model, we need to understand the effect of geological constraints on anisotropy as well as on anisotropic seismic velocity in the study area.

There are a variety of methods to estimate anisotropy for seismic depth imaging. The global function of anisotropy is no longer valid, especially in the complex areas. In this paper we present our practical workflow to incorporate the rock physics from the well and geological information, such as checkshot, calibrated sonic, and geological markers to estimate anisotropy from surface seismic data at well location by using the 1D ray tracing method. This step is very important to tie the seismic events with the well markers into correct depth as well as flatten the common image point (CIP) gathers.

Subsequently, we performed local well tomography to upscale into 3D at the well location. Then anisotropic functions have been propagated along the interpreted seismic horizons using WesternGeco steering filter tool. Finally, the updated seismic velocity field and anisotropic field has been incorporated with estimated dips and azimuths to generate geologically driven anisotropic velocity for seismic depth imaging. This approach has been applied to a study area, in the Green Canyon, in the Gulf of Mexico showing very promising results of seismic images consistent with the well information and geology.

AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.