4D Interpretation of Gas Migration in Shallow Sand Layers

A detailed 4D interpretation using 6 site surveys acquired before and after an underground blow out in 1989 in the North Sea is presented. We compare amplitude and traveltime shifts associated with a 70-80 m thick sand layer at approximately 800 m depth. The well was killed approximately one year after the blow out, and the various surveys cover the period during the blow out and after the well was killed. Our interpretation indicate significant and fairly rapid lateral migration of gas in this sand layer, and also for shallower sand layers. In the next phase this study will be complemented with fluid flow reservoir simulation.