Albertin, Martin L.1 (1) BP America, Inc, Houston, TX

ABSTRACT: Seismic Derived Velocity Models For Drillability Assessment: Resolution Requirements and Scaling Strategies

Moveout based seismic velocity models are commonly criticized for being “too smooth” and “too fast” for use in pressure prediction. Though wave propagation and acquisition parameters do combine to limit seismic velocity resolution, the resolution only becomes an issue when trying to predict short wavelength variations in the subsurface stress field. Despite the importance of detailed pressure information for wellbore planning, predicting the high frequency component of the pressure field from velocity is problematic since the influence of non-stress factors on velocity becomes more significant at a fine scale. Meaningful long wavelength variations in subsurface stress can be detected successfully outboard of allochthonous salt using high fidelity, limited resolution seismic velocity models, but rapid pressure variation details must be integrated into the seismic based pressure estimate via modelling, analog information, or regional geologic trends.
The accuracy of long wavelength pressure estimates ultimately depends on the ability to account for systematic error in the desired vertical velocity field, and applicability of locally calibrated pressure conversion models. Though interval velocity scaling efforts to account for anisotropy can be daunting, when viewed from an average velocity below mudline basis, cumulative anisotropy effects are more apparent, and much simpler to correct. Velocity resolution limits, and the need to minimize scaling induced velocity character, dictate that the anisotropy corrections be smooth in all dimensions.

AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004