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RE: GEOSTATS: Cross-validation, Correlation, and Jackknifing

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  • Tom Mueller
    Syed, You made a good point about the different costs of sampling. But perhaps I don t understand your example about offshore drilling. How can you talk about
    Message 1 of 3 , Dec 9, 1998
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      Syed,

      You made a good point about the different costs of sampling.

      But perhaps I don't understand your example about offshore drilling. How
      can you talk about geostatistics with n = 2 or 3? You are talking about
      applying deterministic models to predict, not geostatistics, right?

      One other point. The reason I'm so concerned with map errors is that for my
      research I've been finding for a number of soil variables that ordinary
      kriging with second order stationary data (fairly well structured) yield
      very inaccurate maps. And that inverse distance weighted gave better
      results than ordinary kriging most of the time. I didn't expect this.
      Today, I would not trust an interpolated map without seeing some
      quantification of map accuracy.

      Tom

      "At the extreme case, for example in an offshore
      environment, two or three delineation wells are all
      that one might afford (e.g., USD 30 million), and
      the subsurface description might have to be built
      deterministically, assuming different "scenarios",
      and incorporating dense (but "soft") information.
      And if one can afford such luxury, perhaps a Boolean
      simulation of sand-shale distributions can be built,
      the basis of which will be a dynamic fluid flow
      model and the detailed design of a USD 500 million
      dollar jackup platform. Whatever the case, samples
      will generally be sparse, and variograms ill-defined,
      and one would have to resort to deterministically
      derived "scenarios" to assess the uncertainty.

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