Seismic velocities

          Seismic velocity is a very important attribute. I ever say: "The Geophysicist Aquiles's heel is the attribute seismic velocity. It is very difficult to do a target depth prevision in a wildcat based on seismic velocities: if You have done an accurate prevision, You made a mistake". In the green banner above You may find a paper about seismic velocities. This paper was presented at 2005 SBGf International Congress. Read it carefully because it carries out too much experience.
Picking seismic velocities
          It is a very important step in Petroleum Industry, ever neglected. In general seismic velocities are picked by inexperienced technicians, so You may guess the job quality is not the required one. Trying to decrease this job impact in quality, it was developed Buscavel tool. You may find more about Buscavel in paper linked above (green banner). Basically this tool access a velocity online database where information about old seismic velocities, checkshot and Time x Depth curves may be visualized in real time by the velocity interpreter. When picking next gather to be interpreted, the same can be done in BUSCAVEL: the tool will search in database for all velocity information close to central gather coordinate (ray user defined, figure bellow).

 

Evaluating seismic velocities

Velana(isotime) and VelanaV(isovelocity) are tools to inspect seismic velocities by map visualization. It is very important to do this, trying to find failures/misties in velocity interpretation. Also it is important to evaluate velocities from every specific 3D to decide about the intrinsic quality of every 3D. Based in this evaluation user may give weights to this quality: these weights are used when doing regional griding of many 2D/3D velocities cubes. See in figure bellow a display from Velana tool.

Editing seismic velocities

VeditOrt is also a unique tool, developed to edit seismic velocities. The technique evaluate a group of velocities simultaneously and point out which velocities are anomalous. The user defines the area (size) to collect and form the group and also defines a target zone (time window) to evaluate velocity deviations. Isotime velocitiy deviations are computed from an averaged velocity function (weighted sum of all velocities in the group): if actual deviation is greater then a user defined value, this function is discarded. Figure bellow is a snapshot of VeditOrt running. Red curves in the right are velocity functions candidate to discard.

Gridding seismic velocities

SuavVel is also a unique tool, developed to grid seismic velocities from many 3D and output an unique 3D velocity cube. After evaluating velocities with Velana and editing velocities with VeditOrt it is time to generate a new Regional 3D velocity cube. To make it more clear, as an example, Campos Basin have a unique seismic 3D velocity cube generated by SuavVel. In SuavVel the 2D/3D velocity cubes are pre-weighted, gridded, smoothed in time/space and finally stacked, and the output is a unique cube. This methodology was partially implemented as plugin in Gocad(Paradigm) and Sigeo(Petrobras package). In figure bellow one may see a slide showing VeditOrt and SuavVel steps.