PESA WA May Evening talk: Pluto 4D monitor two – a second outstanding success

Sandra Mann, Woodside Energy, Australia*
Scott Gagen, Woodside Energy, Australia 

If you’ve ever wanted to keep an eye on exactly where your resources are, this presentation is for you. Hear about how we’re watching gas move using subsurface timelapses on a key Woodside asset. See some great seismic that has helped us learn more about our reservoirs than ever before.

A second 4D seismic survey acquired over the Pluto field has been an outstanding success despite three tropical cyclones, the start of a global pandemic, and technical subsurface risks. At the time of the Pluto 4D Monitor Two (M2) survey (December 2019 till February 2020), the Pluto field had been on production for seven years and nine months and had produced approximately 2 Tcf of gas.

The M2 4D survey was acquired between December 2019 and February 2020 over a 20 x 30 km area. A successful second survey proved repeatability of the technique and the use of modern processing technologies including Full Waveform Inversion, Least Squares Migration and Wave Equation Based Amplitude Versus Offset Inversion facilitated high quality interpretation.

On the 4D difference volumes ‘hardening’ responses were interpreted as commencing and continued water ingress. Hardening responses were seen in some Triassic TR20 and TR30 reservoirs. Examples will be shown. A pronounced response was seen in a large Triassic valley within a predominantly mudstone unit, confirming continued water ingress into the valley and upwards from the GWC in the direction of the producing well. This confined hardening response contrasted with more unconfined, water flood front responses seen in some other intervals. Both responses enabled detailed interpretation of geological features and aided in understanding the dynamic behaviour of the field. Interpreted water ingress also provided additional depth control, an example of which will be shown.