Seismic Velocity Uncertainty Analysis In An Underexplored Basin

In areas characterized by complex geology, Depth Velocity Analysis is the mandatory instrument to estimate the sharp velocity variations that can be expected; seismic data and processing tools are necessary but not sufficient ingredients for successful depth imaging results, so sound a priori information must be retrieved from well information and from the geological knowledge of the area of study, as well as a close integration between the geophysical and geological contexts. A proper estimation of seismic velocities is not only fundamental to obtain good imaging quality and correct depth positioning, but it can also be a key input for detecting the presence of overpressures: usually, overpressured areas are associated with seismic velocity inversions. Moreover, in areas where anisotropy is unknown because of lack of well information, seismic velocities are affected by uncertainty: this must be taken into account in order to quantify the consequent uncertainty both in depth positioning of the target and in pore pressure prediction. In this paper a case history from Offshore Ghana is presented, dealing with the above mentioned issues: the intimate correlation that exists between anisotropy and velocity analysis is investigated, and the impacts of the uncertainty that affects them is considered.