An improved constrained velocity inversion algorithm for geological structures.

In complex geological regions, owing to complex structures and various small-scale local geological bodies, the conventional initial migration layer velocity modeling method is prone to abnormal oscillation and loss of key details of velocity, thereby making the solution of velocity update fall within the local optimum. In addition, this method makes velocity modeling cannot iteratively update quickly and effectively. Hence, in this study, we propose an improved constrained velocity inversion (CVI) method for complex geological regions, which is based on the traditional CVI method, by forming an adaptive velocity trend function. A three-dimensional composite correlation function was introduced into the inversion equation system, through which the nonconstant influence radii and weights that adaptively change with the geological structure characteristics were automatically obtained, and these nonconstant influence radii and weights were also introduced into the inversion equation system. Meanwhile, we processed the key parameters of the adaptive velocity trend function (i.e., the velocity of the geological datum and the gradient of the velocity trend function to depth) by piecewise spline fitting, which further globally constrained the velocity model horizontally to significantly avoid lateral high-frequency anomalies in the velocity model. With theoretical and field datasets, the proposed method resulted in constrained interval instantaneous velocity models, which were well-matched and conformed to the geological structure and features, and further facilitated the imaging quality of pre-stack depth migration in complex geological regions. [ABSTRACT FROM AUTHOR]