| Abstract: | Two dimensional inverse modeling, a process to be applied after standard processing and interpretation, uses interfaces picked by the user. These interfaces are transformed into an approximate subsurface model. The subsurface model is represented by curved interfaces and interval velocities. The interfaces have to be unique functions of the line coordinate. Otherwise they may be arbitrarily curved and may begin or terminate anywhere along the section, e.g., at faults, pinchouts, salt domes and the like. Interval velocities may vary laterally along the section. The inverse modeling algorithm then modifies the model until traveltimes calculated from this model match the traveltimes observed as closely as possible in a least squares sense. The traveltimes corresponding to the model are obtained through ray tracing taking exact account of refraction. The traveltimes observed are the arrival times of single impulses before stacking contributing to the interfaces. These traveltimes are provided by ANAKON, a continuous interface analysis system. The comparison of INMOD results with those of well measurements and those of classical interval velocity computation from seismic data shows the accuracy of the method. Deviations of INMOD derived interface depths are within 2% of well data. |
