Scheduling and Uncertainty in the North Sea

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Scheduling and Uncertainty in the North Sea

• Dr Ken Brown
• Cork Constraint Computation Centre
• University College Cork
• 22nd May, 2003

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Whats in the talk?

• an overview of three real problems from the North
  Sea Oil and Gas sector
• each problem involves resource allocation in the
  presence of change and uncertainty
• the problems illustrate some of the research
  being undertaken at 4C

http//www.nitg.tno.nl/webatlas/images/northsea.gi
f
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Oil pipelines

• pipelines connect oil platforms with onshore
  facilities
• pipelines are assembled onshore, then towed out
  to sea and laid in a trench
• each pipe is a bundled set of smaller pipes

http//www.ukooa.co.uk/issues/storyofoil/productio
n-08.htm
http//www.caithness.org/fpb/june2002/latestwellhe
ad/w8.htm
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Pipeline assembly scheduling

• teams of welders, with skill levels, assemble the
  bundles
• welding tasks and weld tests have expected
  durations
• aim is to schedule the workforce to meet the
  deadline

Aim schedule the welders to meet the deadline,
while minimising expected paid downtime
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Platform maintenance

• Each unmanned gas platform has many components
  and subsystems
• Each part has a recurring maintenance window
• Teams of engineers flown out daily by helicopter
• Maintenance staff must be supported by a stand-by
  vessel within a given radius of the platform
• Aim is to schedule a years worth of tasks,
  minimising costs

http//www.defence.gov.au/army/PILBARA/gallery/ima
ges/Gas20Platform_jpg.jpg
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Dynamic platform maintenance

• BUT
• components fail or platforms go down, and must be
  repaired immediately
• weather conditions shrink the safety radius, or
  even stop the helicopters flying

Aim construct a maintenance schedule robust to
the likely changes
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Container loading

• containers must be laid on deck
• layout must obey safety constraints
• aim is to select the optimal set of containers
  and their optimal layout

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Dynamic container loading

• BUT
• containers arrive at the quayside at uncertain
  times
• the list of containers is not known with certainty

Aim lay out the initial containers giving
flexibility to finish the layout profitably
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Constraint-based solutions ?

• each of the illustrated problems clearly involves
  constraints and optimisation
• finding constraint-based models for the static
  problems is already difficult, but can be done
• the problems are also dynamic, involving
  uncertain knowledge of what the changes might be
• solutions should be in some way robust to the
  changes
• possible approaches include
• the addition of slack time into the schedules
• addition of possible tasks into the problem
• extending search and propagation to reason about
  uncertainty

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Uncertainty research at 4C

• Incorporating uncertainty into constraint models
  and algorithms is one focus of research at 4C
  (Ken Brown, Chris Beck, Toby Walsh, Gene Freuder,
  Rick Wallace, )
• One project funded by Enterprise Ireland will
  start in October, reasoning about likely changes
  to tasks
• The main application area is dynamic or online
  scheduling

We are looking for more industrial problems
please contact us if you think we can help with
your problems
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Questions?