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AI-GEOSTATS:

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  • Laëtitia Mary
    Bonjour, Je travaille actuellement sur un programme devant permettre à terme de cartographier automatiquement la pollution atmosphérique sous ArcView 8. La
    Message 1 of 34 , May 28, 2003
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      Bonjour,

      Je travaille actuellement sur un programme devant permettre à terme de
      cartographier automatiquement la pollution atmosphérique sous ArcView 8.

      La méthode d'interpolation qui a été choisie est le krigeage à
      variogramme sphérique.

      Afin de mener à bien mon travail, je recherche les formules permettant
      le calcul de l'effet de pépite (Nugget), du palier (Sill) et de
      l'étendue principale (major range).

      I currently work on a program having in the long term to allow
      automatically to cartography the air pollution with ArcView 8. The
      method of interpolation which was selected is the krigeage with
      spherical variogramm.

      In order to conclude my work, I research the formulas allowing the
      calculation of the nugget , the Sill and the major range.

      Merci

      Cordialement



      Laetitia MARY

      tel: 04.91.32.38.19






      [Non-text portions of this message have been removed]
    • sebastiano trevisani
      Thank you for your help What make me think in this problem is this (having to perform groundwater flow modeling): If for example I have two lithological
      Message 34 of 34 , Nov 21, 2003
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        Thank you for your help

        What make me think in this problem is this (having to perform groundwater
        flow modeling):
        If for example I have two lithological categories with very different
        spatial structures ( different anisotropy, different variogram ecc..) but
        with the same Hydrogeologic parameters, does grouping these two lithologic
        categories together make sense?(for me not too much!)

        But, and I'm sorry for my English, what I was asking in my mail was not in
        which way I can find the "right" categories. But in which way, once I have
        my categories along the boreholes, I can geometrically discretize the
        boreholes in data to use in simulation or estimation.
        For example I divided a borehole of 10m in punctual values spaced every
        25cm....but probably it is not the best approach.

        Sincerely
        Sebastiano Trevisani

        ---------------------------------------------------------------------------------------------------
        past mails (in geological order!!!!)

        Sebastiano

        The way we do it is to 'composite' samples with the
        same lithology, to a reasonably consistent length.
        Then we do semi-variogram analysis either on each
        lithology separately or at least not pairing samples
        between lithologies. This is an excellent way of
        finding out whether your lithologies have different
        continuity of values or not. Sometimes you can then
        group similar units together.

        Depending on how that stage goes, you can then krige
        within lithologies or in proper 3d.

        Isobel
        http://geoecosse.bizland.com/BYOGeostats.htm

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        -------------------------------------------------------------------------------------------------------------------------

        Sebastiano,

        This is a much debated, classic problem reservoir engineers have in the oil
        industry. To deal with it, I would recommend you first focus on what you
        want your model to do for you. If you plan to build a flow simulation model,
        you need to decide how the different rock types affect flow and how they can
        be grouped to capture different depletion schemes. Rock types generally can
        be grouped together if they have similar properties like porosity,
        permeability, and residual saturations. Another way to identify flow units
        is to plot (by well) cum well permeability vs. depth or cum well
        permeability vs. cum porosity (also called a Lorenz plot), where changes in
        the slope of the plot identify breaks between flow units. If these breaks
        can be correlated across the reservoir, they make nice boundaries for
        geostatistical data points.

        Regards,

        Paul Taylor
        Sr. Reservoir Engineer
        BP

        ----- Original Message -----
        From: "sebastiano trevisani" <sebastiano.trevisani@...>
        To: <ai-geostats@...>
        Sent: Thursday, November 20, 2003 3:21 PM
        Subject: AI-GEOSTATS:

        ---------------------------------------------------------------------------------------------------------------------
        > Hi list members!!!
        > Another question for you!
        >
        > I have to perform geostatistical geological modeling using some boreholes.
        > The litology in these boreholes is described according to geotechnical
        > classification. My question essentially is this: which is the best way to
        > transform boreholes in data to use in geostatical modeling? The
        litological
        > vertical variability is very high, for example I can have layers
        > with thickness of only 10cm. If I discretize the boreholes with a coarse
        > grid (say a step of 50cm) I lose these details (that in the case of a clay
        > layer could be very important from the hydraulic point of view) and if I
        > use a too dense grid I have too many data. For example I tried to
        > discretize borehole data with a grid, along the borehole, of 10 cm,
        > obtaining about 9.000 data. I'm wondering if it could be an idea try to
        > discretize in an "intelligent way", for example trying to adapt the step
        of
        > the grid in relation to the thickness of the level (and why not to the
        > category?) encountered. Or if there is another approach...
        > I have read some books in geostatistical reservoir modeling...but they
        > don't deal with this problem.
        > If some has some idea where to look thank you for your help!
        >
        > Sebastiano Trevisani
        >
        >
        >
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