An Interpreter’s View on 4D with Simultaneous-source Undershoot

Simultaneous-source acquisition is generally considered to be proven technology for land data where is has increased acquisition efficiency. Market acceptance for marine acquisition has been much slower, mainly because of the extra cost of mobilising additional source vessels. But there are situations where extra source vessels are necessary for geophysical reasons, e.g. acquisition of platform undershoot data. Using simultaneous-source acquisition for undershooting would reduce operational time, cost and limit HSE exposure because of the reduction in close-pass operations. Simultaneous-source acquisition introduces interference which must be addressed during processing. For this study real time-lapse data from the Snorre field were used to simulate simultaneous-source acquisition and results were compared with the original, sequentially-acquired, data. Standard 4D attributes indicated a small decrease in repeatability for the simultaneous-source data when compared to the original data and the question to the interpreter was if both datasets were equivalent with regards to 4D usability. Our findings suggest that the observed 4D effects for this particular case are practically the same for the simultaneous-source and the original data. Observations from both datasets would lead to equivalent conclusions with regards to production history matching and reservoir management actions for this field.