Friday 6 January 2012

Gridding and contouring (RMOTC dataset, part VI)

Free geosciences 3D data show GIS helping model reservoir depletion, and displaying it on the desktop and on-line. Then came pipeline routing and now to close the loop is gridding and contouring. Again, this is no replacement for geosciences packages, but rather a tool for triage:
  • first stack as many data as needed (like basin hydrodynamics or land permitting) for play-fairway analyses
  • then focus on targets with geoscience apps on specifics (like seismic and petrophysics) for prospects

Starting with ArcMap 9, 3D Analyst extension under “spline with barriers”  handles grids with faults like we do in petroleum, no small thanks to “the three Steves”, Kopp and Lynch of Esri and Zoraster ex of Zycor. I posted on Arcgis Online the project resulting from this workflow:
  • Jeanette Buelt of RMOTC kindly provided tops for the target producing formation
    (the original dataset only had measured depths, this had true vertical depth and interpreters)
  • join the z-aware wells with the table of target formation tops via the common API code
  • use  “spline with barriers”  from 3D Analyst for gridding
    (tip: make the grid size realistically small, rather than apply smoothing)
  • use  “contour with barriers”  from the same for contouring

Comparing the the contours from data provided by Buelt, shows that working with well tops is a good start. But only seismic will show the closure on the target formation top. Yet the new faulted gridding here shows how important it is to consider faults, typically a challenge in play fairway and prospect analyses. 

click image to enlarge

Fault data are however plain shape files - not z-aware like well data - so that their 3D treatment is limited here. As this is a relatively shallow play, and it is otherwise known that conjugate faults that cut anticline at a high angle tend to be close to vertical (see slide 8 here), the following extrusion in ArcScene is not an inaccurate picture. A simple geometric depiction helps, for example, to ascertain if the “bulls-eyes” at centre below are real or occur across faults - bulls-eyes are contour depictions, in the absence of other data, of adjacent wells with great depth variation  - a fault line running between them may help clean that up, or conversely it may direct geoscientists to look for faults that may have been missed.

click image to enlarge

The most useful aspect here is that one can quickly verify the origin of shallower and deeper tops toward the center of the map. Again GIS is good for overlaying many datasets for data management and triage or clearing, whilst other apps are good for detailed treatment like seismic and petrophysics  or reservoir modeling starting this series.
Beyond traditional visualisation, GIS is thus also used for data management. 

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