Marine time-lapse seismic surveying

Abstract

A method for making a time-lapse seismic survey in a marine environment, the method designed to eliminate multiple surface reflections and changes in sea state and conditions. Seismic sources and receivers are positioned at predetermined conditions for a first set of data in which at least two sets of seismic signals are recorded at each receiver, proximate in time, such that there are insignificant changes in the subsurface formation. At a later point in time the seismic source(s) and receiver(s) are positioned at the same place when the first seismic data set was generated. A seismic source emits a sound wave and the seismic receiver receives what will be called a 'monitor signal' and the two-way water travel time is again determined. A model is then developed for the first and second seismic data sets in that includes the subsurface signal, changes in the subsurface signal and the effect of multiple reflections. A set of filter functions are then developed to filter out the multiple reflections based on the two-way water travel times of the first seismic data set. The first seismic data set, the second seismic data set and the filter function are then used to calculate the differences in the subsurface layers over the elapsed period of time between the two seismic data sets.