NEW COMPUTERIZED METHOD FOR FINDING EFFECTIVE VELOCITY FROM REVERSED REFLECTION TRAVELTIME DATA

A new computerized method is developed using a pair of direct and reversed reflection traveltime curves from two reciprocal shotpoints for finding effective velocity (V//e//f//f) appropriate to the depth of the common-reflection-point (CRP) for a dipping reflector. For the two sets of traveltime data, least-square fits are made to T**2 versus (X**2 plus 4Xd sin theta ), where T is the traveltime for recording distance X, theta is the dip of the reflector, and d is the perpendicular distance from the shotpoint to the reflector. The observed convergence of d for any assumed reflector dip theta , makes it possible to scan through a wide range of theta values by iterative process until the velocities computed by the direct and reversed traveltime data agree within the required tolerance limit, which yields the appropriate effective velocity, and the corresponding theta is the true dip of the reflector. This method simultaneously yields an optimum migrated depth cross-section. It is also possible to study, by this method, velocity distribution in both vertical and lateral directions in the subsurface area under investigation.