Saturday, 29 October 2011

Simple reservoir depletion modelling

Following on last week's Teapot Dome 3D dataset, here's the first step toward upgrading my most popular Slideshare post: Geoscience class notes have an option to run ESRI Model Builder that comes with the Spatial Analyst extension. Simply reversing reservoir topography and applying a surface run-off model, will mimic the depletion of reservoir of its petroleum content. The same way water flows downstream though gravity, petroleum will flow up-slope through hydrostatic recharge (in other words buoyancy pushes hydrocarbons up on top of denser water and out of a reservoir).

click image to enlarge

The purple lines are the flow lines of the modelled fluid flow on an existing raster surface generated by RMOTC. Notice the pooling at the crest of the reservoir, and how some faults affect some but not all flow lines. This is indeed a simple model inspired by Statoil 10-15 years ago, but as a simple model it had some limitations:
  • no rock properties such as porosity or permeability, though that is added in the full class notes
  • surface run-off concentrates the flow lines toward valleys, whereas this model spreads them across reservoir ridges: that could create a very large number of vertices as shown above 
  • and if it appear that some contours acted as barriers, that's an artifice of of drawing vertices 
Next steps will be to simply grid and contour in ArcMap and rerun the model [postponed until I find or create measure shape files with tops data]. The point really is: 
  • to show the power of Model Builder to construct, with simple tools that come with ArcMap extensions, not-so-simple fluid flow in subsurface reservoirs
  • not to replace complete subsurface reservoir modelling packages, only to highlight how much can be done with GIS extension tools out of the box
  • and to allow GIS / Geoscience experts to pass on models to other users, and thus help promote the use of GIS across the organisation 
Again please check my previous blog to find source and background for this nice free dataset.

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