3d estimation

3d estimation performs parameter estimation using kriging and other methods to map 3D analytical data onto volumetric grids defined by the limits of the data set, or by the convex hull, rectilinear, or finite-difference grid extents of a geologic system modeled by gridding and horizons. 3d estimation provides several convenient options for pre- and post-processing the input parameter values, and allows the user to consider anisotropy in the medium containing the property.

3d estimation also has the ability to create uniform fields, and the ability to choose which data components you want to include in the output. There are a couple significant requirements for uniform fields. First, there cannot be geologic input (otherwise the cells could not be rectangular blocks). Second, Adaptive_Gridding must be turned off (otherwise the connectivity is not implicit).

Module Input Ports

• Filename [String / minor] Allows the sharing of file names between similar modules.
• Input Geologic Field [Field] Accepts a data field from gridding and horizons to krige data into geologic layers.
• Input External Grid [Field / minor] Allows the user to import a previously created grid. All data will be kriged to this grid.
• Input External Data [Field / minor]   Allows the user to import a field contain data. This data will be kriged to the grid instead of using file data.

Module Output Ports

• Filename [String / minor] Allows the sharing of file names between similar modules.
• Output Field [Field] Outputs a 3D data field which can be input to any of the Subsetting and Processing modules.
• Status Information [String / minor] Outputs a string containing module parameters. This is useful for connection to write evs field to document the settings used to create a grid.
• Uncertainty Sphere [Renderable / minor] Outputs a sphere to the viewer. This sphere represents the location of maximum uncertainty.

Properties and Parameters

The Properties window is arranged in the following groups of parameters:

• Grid Settings: control the grid type, position and resolution
• Data Processing: controls clipping, processing (Log) and clamping of input data and kriged outputs.
• Time Settings: controls how the module deals with time domain data
• Krig Settings: control the estimation methods
• Data To Export: specify which data is included in the output
• Display Settings: applies to maximum uncertainty sphere
• Drill Guide: parameters association with DrillGuide computations for analytically guided site assessment

For additional information on kriging speed, memory requirements and performance please see the Performance Benchmarks page.

 

Variogram Options: 

There are three variogram options:

1. Spherical: Our default and recommended choice for most applications
2. Exponential: Generally gives similar results to Spherical and may be superior for some datasets
3. Gaussian: Notoriously unstable, but can "smooth" your data with an appropriate nugget.

I specifically want to discuss the pros and cons of Gaussian. Without a nugget term, Gaussian is generally unusable. When using Autofit, our expert system will apply a modest nugget (~1% of sill) to maintain stability. If you're committed to experimenting with Gaussian, it is recommended that you experiment with the nugget term after EVS computes the Range and Sill. Below are some things to look for:

• If you find that Gaussian kriging is overshooting the plume in various directions, your nugget is likely too small.
• However, if the plume looks overly smooth and is too far from honoring your data, your nugget is likely too big.

The "Power Factor" is only used for exponential or gaussian variograms. The default value of 3 is the most common value used for exponential in most software. For gaussian, 2 is most common, though anything from 0.1->3 is typically acceptable. This is effectively the "a" term described here: https://en.wikipedia.org/wiki/Variogram#Variogram_models

 

Advanced Variography Options:

It is far beyond the scope of our Help documentation to include an advanced Geostatistics course. The terminology and variogram plotting style that we use is industry standard and we do so because we will not provide detailed technical support nor complete documentation on these features, which would effectively require a geostatistics textbook, in our help.

However, there is an Advanced Training Video on how to take advantage of the complex, directional anisotropic variography capabilities in 3d estimation (which applies equally well to lithologic modeling). This class is focused on the mechanics of how to employ and refine the variogram anisotropy with respect to your data and the physics of your project such as contaminated sediments in a river bottom. The variogram is displayed as an ellipsoid which can be distorted to represent the Primary and Secondary anisotropies and rotated to represent the Heading, Dip and Roll. Overall scale and translation are also provided as additional visual aids to compare the variogram to the data, though these do not affect the actual variogram.

We are not hiding this capability from you as the Anisotropic Variography Study folder of Earth Volumetric Studio Projects contains a number of sample applications which demonstrate exactly what is described above. However, we assure you that understanding how to apply this to your own projects will be quite daunting and really does require a number of prerequisites:

• A thorough explanation of these complex applications
• An understanding of all of the variogram parameters and their impact on the estimation process on both theoretical datasets as well as real-world datasets.

This 3 hour course addresses these issues in detail.