Geologic 3D velocity model in Keathley Canyon and Walker Ridge, Gulf of Mexico

Abstract

This 3D velocity model was constructed using high-resolution 2D seismic data with 15 km offsets and 22 s of record for which a Kirchhoff depth migration produced a 40 km (130,000+ ft) depth record constrained by sonic logs from 94 wells, 34 vertical seismic profile or borehole seismic velocity surveys, and 38 calculated time versus depth tables derived from other borehole data. All forms of sonic information were loaded into a velocity modeling application in an interval velocity (Vint) versus depth format. Comparison of the resultant 3D velocity model with available constraints shows that regional geologic trends expressed in the 3D Vint model faithfully reproduces the observed borehole Vint profiles at 18 locations where the seismic velocity control is in close proximity to measured borehole velocity data. The sonic velocity for salt from 13 of these boreholes matches the seismic salt velocity within 2%, and another four wells match within 5%. Zones of overpressure (anomalously low Vint) and zones of Cenozoic limestone (anomalously high Vint) are discernible within the velocity model. Stratigraphic layers of equal Vint displayed with a “random” color bar closely mimic structural trends within the 3D velocity model and tie reasonably well at the intersection between seismic and wellbore velocity control. The resultant 3D “cube” of Vint values covering Keathley Canyon, Walker Ridge, and a portion of Green Canyon shows many distinct velocity trends and features that are confirmed by well control.