ABERDEEN Here’s a snapshot of some of the technical presentations that rounded off 2012 for SPE Aberdeen and London Sections.
Technical Presentations Roundup
In October, at the Douglas Hotel, SPE Aberdeen welcomed Mariano Floricich, a Reservoir Geophysicist with Shell U.K. Ltd, who presented ‘4D seismic and reservoir engineering: best friends or annoying neighbours? – examples from the North Sea’.
Mariano engaged his audience by demonstrating the concept of 4D, or time-lapse, seismic using two boxes containing one-and-a-half crayons, which were circulated around the audience to see if anyone could guess which of the boxes held which size of crayon.
“Intuitively, we try to shake the box (ie send some vibrations to the earth) and listen (ie record the sound waves),” he explained. “We do this twice, once for each box (ie at different production times) and we use the difference in the sound to predict which one has the shortest crayon (ie look at the sound waves difference to assess changes in the reservoir).”
that time-lapse seismic data has generated significant value and enabled further development at Gannet F both by optimising well placement to drain the main Forties accumulation and identifying unexpected fluid flow between unpenetrated reservoirs. It has also shown that inter- reservoir connectivity is dominated by sand-sand communication through fault juxtaposition. Finally, integration with static and dynamic models, conceptual geological models and other geophysical techniques has allowed further infill opportunities to be identified, specifically targeting the field’s southern reservoir units.
Turning to the Norwegian Draugen field, Mariano explained how ‘World- class 4D seismic data has identified new infill targets in a mature field’. This achievement has come about as a result of the integration of all information and the use of four monitor surveys, each of which has added information and value – the fourth being essential to attic drilling and the asset’s plan to drill some new wells later this year.
He concluded his talk by sharing the following key learnings:
• 4D time-lapse seismic has become a frequent tool for reservoir monitoring in the North Sea – mainly for Paleocene/Eocene deepwater turbidite reservoirs, but there are also some examples from Cretaceous (chalk) and Jurassic/Triassic reservoirs.
• 4D seismic should also become a frequent tool for asset optimisation, as it impacts the right HSE and business decisions at the right time.
• Integration of all available information is key. This is easy to say but not always easy to do! We need to start with a good understanding of the 3D static subsurface model, in terms of: structure (ie seismic interpretation, depth conversion, geological setting); facies and petrophysical properties (probabilistic seismic inversion for properties prediction), and volumes in place (are those volumes supported by material balance?).
• The challenge is to generate workflows that allow fast and efficient updates of static and dynamic models every time new data arrives (ie use of 4D seismic inversion to update history-matched dynamic model).
You can download Mariano’s full presentation from the Aberdeen Events section at: www.spe-uk.org
This year’s SPE Aberdeen evening meeting programmes are kindly sponsored by Archer and Shell.
He confirmed that over the last 15 years, the process of building static/ dynamic models and interpreting 4D seismic has gradually involved the integration of all subsurface disciplines. Geophysics, Geomechanics, Geology, Geostatistics, Geomatics, Reservoir Engineering, Petrophysics, Production Technology, Geochemistry and Well Engineering today work closely together to create the best representation of the subsurface within a static/dynamic model.
4D seismic enhances field development in a number of ways, he said. It reduces subsurface uncertainty on drainage patterns, connectivity, compartmentalisation and scenario choice, facilitating better HSE performance in terms of drilling safely into partially depleted reservoirs, blow-out monitoring, safe injection monitoring and safe disposal monitoring. An improved static and dynamic model provides better forecasts and better plans and leads to improved field performance through better producer and injector well positions, and the ability to control existing wells to increase rates, avoid water breakthrough and reduce water/gas production.
Mariano then introduced two case studies from Shell’s North Sea portfolio. ‘Gannet-F: big value from a small field’ described the results of 14 years of using 4D in the Gannet Cluster development and, in summary, explained
In November, Pete Naylor, BG Group Principal Consultant, Decision Risk Analysis, opened SPE London’s evening meeting at the Geological Society with ‘VOI: Value of Information (or Very Opaque Inferences?)’ which explained the ‘when, why and how’ of VOI for those who need to decide whether it is worth investing time and money in acquiring additional data for field development.
Producing decision-relevant information is a key task for petroleum engineers and geoscientists, and some of the most important decisions are concerned with what type and quality of information to produce. As information gathering can involve very high-cost activities, such as seismic surveys, core and well test analyses and reservoir simulations, decision analysis can be a valuable tool in enabling us to distinguish between constructive and wasteful information gathering. Within that framework, VOI analysis helps us to evaluate the benefits of collecting additional information before committing resources.
Pete began by explaining that VOI analysis might be valuable when: facing a number of decisions; outcomes are uncertain; there is an opportunity to acquire additional information, and the information costs money or time. “If any one of these statements does not apply, then there is no point in undertaking a VOI analysis,” he said.
The reasons why additional information might be valuable include the possibility that the magnitude of future uncertainties will be reduced, and that decisions may change in the light of the new information. A simple
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