Composite borehole data

Composite borehole data is a type of compositing interpretation where samples within a geological zone or borehole are composited into intervals. You can weight the grades or qualities by length or other options (like, specific gravity or recovery).

This page discusses:

About composite borehole data

To create composites, you must first select a previously created interpretation (See Creating and Viewing Geoscience Reference Data) and then, select a composite type. The two types of composites are:

  • Downhole composites: Creates composite samples of a specific length. The resulting composites are downhole composites of equal length.
  • Composite within units: Creates composite samples based on geological constraints. The resulting composites are bulked samples of different lengths.

Downhole composites: Composite length method

The composite length method is only used for downhole composites. The method is used to calculate the lengths of the composite intervals. The two types of composite length methods are:

  • Fixed length: Creates samples of equal length. The length is the Composite Length value that you have defined.
  • Best fit: Creates samples of different lengths within a geological zone. Samples are created within the zones that you select. If any part of the composite remains in the zone after dividing the length of the zone by Composite Length, the width of each composite (within the zone) is changed so that the composite widths are even.

Weighting attributes

You can select weighting attributes to modify the values of generated composites. You can weight the resulting grades or qualities by length only or by other attributes. You can apply weighting:

  • Globally (to all interpreted attributes): Applied when the weighting attributes are the same for every attribute.
  • Individually (select weighting attributes for each interpreted attribute): Applied when the weighting attributes are different for every attribute

Short samples

Short samples represent rejected composites. Samples may be rejected if limits on weighting attributes are defined or the minimum percentage of sample to be included is defined.

Limits for each weighting attribute determines if a sample is short. The value of limits for each weighting attribute determines if a composite sample provides sufficient support for subsequent geostatistical evaluation. If a weighting attribute of recovery (%) is used, an appropriate cutoff value might be 90%. This is then used with the Minimum percentage of sample length to determine if a composite sample is short or not.

  • Limits: Sample is short if any weighting attribute value is not equal to or greater than the defined limit for that weighting attribute.
  • Minimum percentage of sample to be included: for the calculated composite length, this percentage of the length must contain samples, otherwise it is considered short.