Core to Log Comparison

Composition Graph

We use an Excel spreadsheet to set up the matrix algebra solution for compositional analysis. The MINVERSE function within Excel is used to perform the operation through inversion of the matrix of the log properties of the components.
The logs used in the composition analysis are: Gamma Ray, Neutron Porosity (percent), Bulk Density, and Photoelectric Volumetric Cross Section. By premultiplying the logs by this inverse matrix, we can determine the percentage of calcite, dolomite, quartz, shale, and porosity.

 

• Mineral compositions estimated from the logs show good concordance with lithologies described from core.
• The composition graph is a useful quantitiative representation of lithofacies, porosity, and amount of dolomitization observed within each core.
• Porosity computed from average neutron-density porosity logs shows a fair correlation with porosity measured in core.

Composition graphs using GR, Neutron porosity (percent), Photoelectric, Grain Density, and Bulk Density.

 

Porosity Comparison

Porosity from core analysis is plotted against Neutron Density Average porosity from logs. There is a fairly good match between the two data sets for the Spergen section.