Movie showing a 4D difference volume between the 1999 and 1993 surveys BagleyG. SaxbyI. McGarrityJ. PearseC. SlaterC. 2019 This movie shows a 4D difference volume between the 1999 and 1993 surveys rendered only where reservoir units have been defined, from an interpretation of the baseline data. Areas of difference are now clearly shown to correlate well with producing wells and the zone of pressure drop away from wells can be inferred from the extent of difference away from well bores.