Geological Sciences

Petrology and Mineralogy

X-Ray Powder Diffraction (XRD)
Used to determine composition of rocks and other crystalline material. It is the best way to determine amounts and types of clay minerals.

  • Bulk Analysis - Material is ground to a fine powder. Results are reported in weight percent. Useful for scales or rock samples where clays are not present .
  • Formation Rock Composition - Includes a bulk analysis of all mineral components and analysis of the less than four-micron clay size material. The clay-size fraction is analyzed separately from bulk components, then recombined to provide the total composition of the rock. Reported results all minerals present in the rock and includes types and amounts of clay minerals and are reported in weight percent.
  • Organic Shale Analysis - Analysis incorporates organic component (TOC) with inorganic constituents of rock. Reported results are in weight percent, volume percent, and include grain density calculated from XRD data.
  • Siliceous shale analysis (Crystallinity Index /Silica Diagenesis) - Analysis included detailed analysis of quartz peaks to determine index of crystallinity which directly relates to the degree of silica diagenesis.

Scanning Electron Microscopy (SEM)
Provides high magnification/high resolution images of smallest features in rocks.

  • Standard SEM analysis - Used to investigate authigenic clays and other cements associated with pore systems of conventional reservoir rocks. Analysis done in a low-pressure chamber using samples coated with gold or gold/palladium alloy.
  • Mudrocks - SEM used to investigate micro-and nanopore systems in unconventional reservoir rocks. Analysis done in a 'high-pressure' SEM chamber with uncoated sample.
    • Argon-ion milling used to prepare surface of sample for analysis. Ion-milling provides a polished surface suitable for backscattered electron imaging.
    • Backscattered Electron imaging. Used to reduce/eliminate charging effects on uncoated samples.
  • Energy Dispersive Analysis of X-Rays (EDX)
    • Qualitative Analysis - used to identify elemental composition. Can be used to identify framework grains or cements in a reservoir rock, or to identify layers/bands in a scale.
    • Dot maps - EDX data can be used to illustrate the distribution of elements in a SEM image.

Thin Section Petrography

  • Descriptions - A detailed description of the texture, framework grains, pore system, and authigenic minerals identified in a thin section. Useful to describe mudrock, siltstone, and some limestones (mudstone, wackestone, boundstone).
  • Point Count - Used in addition to a thin section description - provides compositional data based on framework grains, cements, and matrix.. Used to describe sandstone and some limestone (grainstone).
  • Touchstone petrography - Petrography used in Touchstone based Reservoir Characterization Models. Includes minimum 300-count point count, 100 framework grain measurements, and estimation of grain coating on a minimum of 50 framework grains.

Additional Petrology Information

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