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Pluto 4D – Australia’s first 4D over a gas field is an outstanding success
Larry Tilbury
The Pluto 4D seismic survey is Australia’s first 4D acquired over a gas field and has been an outstanding success despite the prior high technical risk of not being able to detect 4D differences above the background noise. At the time of the Pluto 4D monitor survey, the Pluto field had been on production for three years nine months and produced approximately one Tcf of gas.
The first monitor survey was acquired by PGS between November 2015 and February 2016 using dual sources and 12 by 7050m streamer (geostreamer) configuration. Of note were the use of steerable sources to assist with repeatability, and towing the streamers deep (20m) to minimise noise. Data was processed by CGG to Pre-Stack Depth Migration, took 12 months to deliver, and required significant interaction between Woodside geoscientists and CGG to ensure an excellent 4D product.
4D feasibility studies carried out prior to acquisition showed that saturation changes (related to water ingress) were expected to show strong 4D responses near the gas water contact (GWC), and would be interpretable if the monitor survey was run after approximately 3 to 4 years of production. If the monitor survey was delayed it showed that the pressure response became too large, swamped the 4D differences, and made interpretation difficult or impossible.
Strong “hardening” responses on the 4D difference volumes are interpreted as water ingress into the field. “Hardening” responses are seen in all reservoir sequences in the Triassic from the TR27 to the TR32 units and range from strong (obvious) to weak (possible). Several examples are shown – the strongest response is seen in the large Triassic (TR27.3) valley within an essentially shale prone unit, which shows water ingress into the valley and moving upwards from the GWC towards the producing well.
The results/insights from the 4D data have provided excellent control points for the history matching of the Pluto Field.
Cost:
$68 for PESA Members (early bird price)
$98 for non members
$78 for all PESA members who book after 16th July
$38 for students (early bird price)
$58 for graduate, retired and hardship members (early bird price)
Early bird closes Monday 16th July 5pm, all registration close Tuesday 17th July 5pm
