Early Insights from the Second 4D Monitor Survey over the Catcher Fields

A second 4D monitor survey has been acquired over the Catcher Fields in block 28/9a of the North Sea. The first early-out data were delivered six weeks after acquisition in July 2024. Since then, time-lapse data conditioning has been applied to enhance the repeatability of the data and calculate time shifts for time alignment. A 4D pressure and saturation inversion was run to quantify the production-induced changes in the reservoir.

The early-out data confirmed the expected dynamic behaviour of the reservoir in most places, but there were a few surprises. An unexpected softening signal was observed in the Cromarty reservoir, which is believed to be caused by a small decline in reservoir pressure and gas exsolution. Production data indicated that the eastern area of the Burgman field was partially isolated, which led to a localised pressure decline and gas exsolution. A strong softening signal and time shifts below the reservoir confirmed this; however, small time shifts above the reservoir suggested a subtle stress-arching effect. Full-integrity processing is currently underway. This includes 4D full waveform inversion (4D FWI) to estimate separate velocity models for migration. The results will be used to confirm and refine the interpretations from the early-out processing.