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Book Chapter

Re-saturation targets identified from 4D seismic softening responses in the Forties Field

By
Lyndsay Singer
Lyndsay Singer
Apache North Sea, Caledonia House, Prime Four Business Park, Kingswells Causeway, Aberdeen AB15 8PU, UK
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Grant Byerley
Grant Byerley
Apache North Sea, Caledonia House, Prime Four Business Park, Kingswells Causeway, Aberdeen AB15 8PU, UK
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Phil Rose
Phil Rose
Apache North Sea, Caledonia House, Prime Four Business Park, Kingswells Causeway, Aberdeen AB15 8PU, UK
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Published:
January 01, 2018

Abstract

A novel 4D methodology by targeting softening responses, a decrease in impedance over time, is described from the Forties Field. It is demonstrated that these anomalies identified areas where oil had re-saturated previously swept rock. When first observed in some of the older vintages of 4D data, softening responses were dismissed as side lobes of underlying water-swept reservoirs. With improved 4D data quality, softening responses were seen to be clearly responding to an acoustic softening effect isolated in the reservoir. Pressure measurements ruled out hypotheses of gas exsolution or geomechanically induced dilatation of the overlying shale.

At the time of writing 22 re-saturation targets had been drilled at Forties with an average water saturation (Sw) of 28%, close to virgin conditions. These results indicated that a previously swept sand can be re-saturated to near initial oil conditions.

The driving mechanism behind the re-saturation is understood to be related to changes in both production offtake and water injection. The resulting complex hydrodynamic interactions appeared to be moving banks of oil around the field. From 2011 to year-end of 2015 re-saturation targets produced 14.6 MMBO and were a key target type at the Forties Field.

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Contents

Geological Society, London, Special Publications

Petroleum Geology of NW Europe: 50 Years of Learning – Proceedings of the 8th Petroleum Geology Conference

M. Bowman
M. Bowman
University of Manchester, UK
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B. Levell
B. Levell
University of Oxford, UK
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The Geological Society of London
Volume
8
ISBN electronic:
9781786203151
Publication date:
January 01, 2018

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