Abstract:

Seismic interval velocity is an important parameter for the Carboniferous exploration in Eastern Qaidam Basin. Interval velocity can be applied to timedepth conversion, and to reflect lithological, structural and formationpressure information. Seismic section is closely related to seismic velocity. Because of Carboniferous data shortage in Eastern Qaidam Basin, seismic velocity has long been a problem, and the velocity error in the timedepth conversion was large. To solve these problems, a new approach to calculate interval velocity was presented based on the previous work, thus improved the velocity accuracy and better understood the tectonic and geological characteristics in Eastern Qaidam Basin. Seismic stack velocity was converted into root mean square velocity based on the single well velocity analysis and multiplepicking of twodimensional seismic stack velocity, and then was converted into interval velocity using constrained Dix inversion based on the singlewell velocity trend model, at last the fitting curve of the average velocity field was done. Then, the seismic average velocity was corrected by well logging velocity as the control points, so as to establish a more reasonable interval velocity model. The new depth structure converted by the new interval velocity model is more reasonable than previous one. The new velocity model for calculating interval velocity is more accurate than the previous results, more in line with the singlewell velocity trend and is consistent with the geological cognition.

Key words: Qaidam Basin, target process, stack velocity, trend model, Dix formula, velocity inversion, Carboniferous, velocity field