Pluto 4D—Australia’s first 4D over a gas field is an outstanding success
Larry Tilbury A B and Andre Gerhardt AA Woodside Energy Ltd, 240 St Georges Tce, Perth WA 6000.
B Corresponding author. Email: larry.tilbury@woodside.com.au
The APPEA Journal 58(1) 395-411 https://doi.org/10.1071/AJ17096
Submitted: 4 December 2017 Accepted: 16 January 2018 Published: 28 May 2018
Abstract
The Pluto 4D seismic survey is Australia’s first 4D survey 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 and nine months and produced approximately 1 Tcf of gas.
The first monitor survey was acquired by PGS between November 2015 and February 2016 using dual sources and 12 streamers of 7050 m (geostreamer configuration). Also of note was the use of steerable sources to assist with repeatability, and towing the streamers at 20 m to minimise noise. Data was processed by CGG to pre-stack depth migration (PreSDM), 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 before 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 three to four 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.
Keywords: gas expansion, history matching, Pluto gas field, reservoir monitoring, rock physics, water ingress, 4D feasibility, 4D interpretation.
Larry Tilbury graduated from the University of WA in 1971 with a BSc (Hons) in Physics and Mathematics. His working career spans more than 45 years, including 10 years (1971–81) as a geophysicist in the Marine Group of the BMR where he worked in acquisition, processing and interpretation in most of the offshore basins of Australia, and more than 35 years with Woodside (since 1981) working as an interpreter in exploration and development on the North West Shelf of Australia and the Gulf of Mexico. He is the Principal Geophysicist in the Pluto Development Subsurface Team currently working on the recently acquired Pluto 4D and high-resolution Pluto 3D. His main interests are 3D and 4D interpretation, particularly image processing and seismic inversion studies for reservoir characterisation. He is a member of SEG, ASEG, PESA and EAGE. |
Andre Gerhardt has been involved in a broad spectrum of geophysical technologies ranging from seismic acquisition and processing to quantitative interpretation and reservoir monitoring for almost 30 years. He is currently a Technology Manager with Woodside Energy and previously the Head of Quantitative Interpretation. He is also in charge of Seismic Amplitude Analysis and Risking, with broad experience analysing prospects and opportunities worldwide. Andre has worked on several time-lapse projects in Australia and abroad and is currently working on technologies that enable identification of residual gas, amongst others. Andre has previously worked for Petrobras and holds a BSc in Geosciences and an MSc in Computer Science. |
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