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GEOSTATS: Sampling.Grid

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  • luftdruck
    Hello . . . I am a Hydrogeology Master s student with a sampling grid question. I will be sampling a number of vertically exposed sedimentary beds which vary
    Message 1 of 3 , Jun 4, 1997
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      Hello . . .

      I am a Hydrogeology Master's student with a sampling grid question.

      I will be sampling a number of vertically exposed sedimentary beds which
      vary in thickness between 10 and 160 cm. Geostats will be performed on
      each of these beds individually as well as for the complete data set.
      I realize that I need a regularly spaced sampling interval with 30-40
      samples per bed. The necessary grid will need to be very fine for the
      thin beds. If I apply this same grid to the thick beds, my sample
      population will be extremely high and will necessitate an overload
      of analyses.

      Would it be statistically correct to generate a sampling design which
      includes 30-40 samples per bed with sample spacing that is *proportional*
      to the bed thickness? If not could you give me some other suggestions?

      Thank you very much for your time.

      Michael Pickering
      Washington State University
      six41@...

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    • Med Bennett
      ... What are you sampling for and attempting to interpolate? Are you trying to interpolate along section (1D), across the outcrop (2D), or in three dimensions?
      Message 2 of 3 , Jun 9, 1997
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        At 12:32 PM 6/4/97 -0700, you wrote:
        >Hello . . .
        >
        >I am a Hydrogeology Master's student with a sampling grid question.
        >
        >I will be sampling a number of vertically exposed sedimentary beds which
        >vary in thickness between 10 and 160 cm. Geostats will be performed on
        >each of these beds individually as well as for the complete data set.
        >I realize that I need a regularly spaced sampling interval with 30-40
        >samples per bed. The necessary grid will need to be very fine for the
        >thin beds. If I apply this same grid to the thick beds, my sample
        >population will be extremely high and will necessitate an overload
        >of analyses.
        >
        >Would it be statistically correct to generate a sampling design which
        >includes 30-40 samples per bed with sample spacing that is *proportional*
        >to the bed thickness? If not could you give me some other suggestions?
        >
        >Thank you very much for your time.
        >
        >Michael Pickering
        >Washington State University
        >six41@...
        >
        What are you sampling for and attempting to interpolate? Are you trying to
        interpolate along section (1D), across the outcrop (2D), or in three
        dimensions? Geostats may be overkill or inappropriate if you are trying to
        quantify changes vertically through the section (depth or time).
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      • Syed.R.Syed@EXXON.sprint.com
        Michael Pickering s questions refer (i.e. using sampling interval proportional to bed thickness): 1. It s good to be familiar with: (a) what the end result
        Message 3 of 3 , Jun 10, 1997
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          Michael Pickering's questions refer (i.e. using sampling interval
          proportional to bed thickness):

          1. It's good to be familiar with: (a) what the end result will be used
          for; and, (b) what scales of heterogeneity will most impact that
          end result. E.g. in a petroleum deposit, lamina scale heterogeneity
          may or may not impact a fluid flow process, therefore sampling must
          take into account this knowledge, regardless bed thickness.

          2. It's even conceivable that a smaller bed might not show as much
          heterogeneity as a thicker bed, i.e. due to erosion of part of the
          smaller bed. That thicker bed might show varying scales of
          heterogeneity which the sampling should try to capture as much as
          possible. Some intuitive decisions need to be made.

          3. Re: (1) and (2) above, I suggest that the sampling scheme be based
          on some sound subjective (geological) understanding of the phenomena,
          and a knowledge of the impact of the eventual description on whatever
          transfer function will be applied (whether fluid flow simulation or
          otherwise). The problem isn't as tractable as it "seems" no matter
          how statistical you want to make it.

          Regards, Syed

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