Fast 3D azimuthal velocity analysis

Azimuthal dependence of rock properties is of interest for at least two reasons: first, it may be due to azimuthally<br>aligned fracturing, and second, it can be used for enhanced directional and horizontal well planning. One of the main<br>tools for detection and evaluation of such a dependence is azimuthal velocity analysis. Commonly, the procedure is<br>based on calculation and interpretation of horizontal semblances along target horizons. The procedure is rather timeconsuming<br>and requires thorough lateral averaging. We propose a fast technique providing high lateral resolution maps<br>of anisotropy coefficient v) of elliptical ( v) = v)) horizontal transverse isotropy (HTI) model, orientation of the HTI<br>symmetry planes, and maps of velocities along the symmetry planes. The technique is based on a known procedure of<br>mapping residual moveout delays between near and far offset stacks. Distinguishing feature of the technique consists in<br>a set of specific computational procedures leading to unbiased, statistically efficient and relatively stable estimates of<br>the HTI model parameters at every bin of 3D survey area. The set includes depth prestack migration weighted so as to<br>flatten the offset distribution over azimuths inherent in the acquisition grid, calculation of reference offsets for every<br>angle stack, and a deterministic explicit scheme of regularized estimation of HTI parameters.<br>High resolution of the technique is exemplified by azimuthal velocity analysis on an oil field in West Siberia combined<br>with azimuthal analysis of reflectivity and geomechanical modeling of pore pressure and principal horizontal stresses<br>responsible for fracturing origin and evolution.