Mineral Inversion Module

Purpose

The Mineral Inversion module empowers users to determine mineral volumes and grain density. The module utilizes a matrix inversion that takes a lsit of minerals and the measured curve responses and solves for the mineral and fluid volumes at each depth step. This provides a powerful way to analyze for porosity in complex and mixed lithology systems.

Primary Outputs

The following curves are the primary interpretations made in this module.

Screenshot showing mineral inversion tracks.

Discussion

Mineral inversion is often thought of as a "black box" calculation. However, in reality it is a simple matrix inversion that is performed using logical constraints (e.g., total volume must sum up to 100%, no individual component can be less than 0% or greater than 100%) and weighting factors to ensure that each curve has the proper influence.

For those who are new to mineral inversion, the layout will appear different than that of other modules in Danomics - this is because we need to work with a matrix of properties and curves for each zone. There are two property matrices - the "Mineral matrix" and the "Curves matrix", explained below with associated screenshots.

Mineral matrix:

• Zone: Select the zone (or default) for modification.
• Mineral: The name of the mineral in the model.
• Enabled: Checkbox to specify if the mineral will be used in the inversion for the active zone.
• Grain: Specify if the mineral is part of the matrix (checked) or a fluid (unchecked).

Screenshot showing the minerals matrix containing the list of minerals to consider and their corresponding properties.

Note that the mineral properties given on each row correspond to the curve listed in the Curves matrix.

Curves matrix:

• Curve: Dropdown menu with available curves. User can also type in a curve name.
• Mode: Specifies how the curve will be used in the inversion.
• Conf. Int: Places a weight on the curve in the inversion. Smaller weights increase importance. Should be set relative to curve value range.

Curves matrix showing the curve name, the fit mode, and the weighting factor.

In general when performing the interpretation it is important to recognize that most mineral properties are well understood with very little variation. This means that most effort should be placed on:

1. Ensuring that a minimum viable mineral mix has been selected. Try to keep the number of minerals to what is needed. If a mineral is only present in trace amounts (e.g., zircon) it is probably better left out. Additionally, set mineralogy by zone - if one zone has salt, but the others don't, ensure that mineral is only active in that particular zone.
2. Focus on the components that can vary - clay, kerogen, and the fluids. Clays, for example can vary substantially with respect to their density, neutron, pe, and sonic values. So focus on those first. Next consider the fluid densities - especially the oil and/or gas density.
3. Consider activating the param to not perform the inversion calculations when specified curve(s) are not present. E.g., if the bulk density curve is not available you may not want to run the inversion. Use the parameter to limit this and specify what curves must be non-null.

When setting the parameters expand the window so that the mineral and curve matrices are aligned. This will make it easier to see which properties tie to which curves.

Please see this article for additional information on the theory behind mineral inversion: Mineral Inversion at Scale.

Other helpful videos, such as this tutorial video can be found on the Danomics YouTube channel.