Geophysical Prospecting: Controlled source strength variation by changing the firing pressure ‐ a sensitivity study for 4D calibrationFor a 4D seismic operation to be successful, it is important to know what kind of 4D signal we expect to observe, as well as its magnitude. Normally, in a 4D feasibility study, we use rock physics models to quantify the effect of fluid or pressure changes within the reservoir and calculate the corresponding effects to the seismogram. However, to find if the predicted changes are actually observable at a given field, a dedicated calibration procedure might give valuable insight. One such procedure for marine seismics is to gradually change the source strength by varying the firing pressure in order to detect the sensitivity threshold for a given subsurface reflection. This procedure would be practical and feasible if the change of the source signature changes linearly with the source pressure. However, non‐linear effects will lead to minor changes in the later arrivals of the source signature, the so‐called bubble. By investigating these introduced errors for a reasonable air‐gun array we conclude that the method is still feasible since we find it possible to control and diminish the impact of the introduced errors.
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