PESGB Evening Lecture: December 2020

Topic: 20 Years as a 4D Practitioner. Speaker: Jonathan Brain - Shell UK Ltd (Joint event with EAGE)


1st December 2020

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Joint event with:

Speaker: Jonathan Brain – Shell UK Ltd
Topic: 20 Years as a 4D Practitioner

Since joining Shell 20 years ago, Jonathan Brain has worked on over fifty 4D seismic projects in Europe and consulted on many more globally. In this talk he will reflect on the common themes he’s observed and consider what makes for a successful project and ultimately business value. He will argue that the value of 4D far exceeds the estimates of upfront VOI studies and that the shelf life of a 4D survey is much longer than expected. On the flip side, he will also address the potential pitfalls when introducing 4D seismic data to a subsurface team, such as the need to include interpretation uncertainty, non-uniqueness, data integration and a suitably wide scenario space in the analysis. He hopes this talk will go some way to explain why he’s still excited to start every new 4D project, even if it is the 6th monitor on a mature field.

To help him illustrate, he will follow the evolving use of 4D seismic at the Shearwater field, which has also just celebrated its 20th anniversary. Shearwater is a HPHT field in Central North Sea, producing gas condensate, mainly from Jurassic Fulmar sands. After an initial period of strong depletion, the wells started to experience mechanical failure as a result of compaction induced stress changes in the overburden. By 2009 all the original producers had failed and there was no production from the Fulmar in the main block. After overcoming the considerable technical challenges of drilling a highly depleted reservoir with a weakened overburden, two Fulmar reinstatement wells were successfully completed, and production was resumed in 2015. However, the Fulmar reservoir well in the Eastern panel experienced water cut within a year of start-up and further infill opportunities were matured using 4D seismic. Currently, drilling the second well of a three well campaign. 4D has helped to drill safely through the overburden, identify depleted reservoir and map water influx, but has also added value in some other surprising ways over the field life.

He will also take the opportunity to introduce some new workflows, such as 4D velocity model updating to correctly image the monitor surveys. This has proved important for calibrating geomechanical models and identifying the position of weakened overburden at the crest of the field. There is still much to learn from the Shearwater data and many outstanding challenges for 4D seismic generally, but this is exactly what makes the job fun.

Figure 1:




(a) Seismic cross-section across the Shearwater field with stratigraphy overlaid.
(b) Geobodies of water sweep interpreted from 4D seismic for three successive time steps. In the most recent, water is seen reaching the Eastern Panel producer.
(c) Top Fulmar interpretation and production wells with overburden 4D time-shifts in colour. Time-shifts have been used to interpret reservoir depletion, calibrate geomechanical models and identify drilling hazards in the chalk.

We would like to thank the Shearwater co-ventures, Esso Exploration and Production UK Limited and Arco British Limited for permission to share this material.


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