Tag Archives: Petrography

Optical Microscopy

We make extensive use of optical microscopy for both collection of petrography data (textural and modal analysis) and also for more descriptive work.

We are well equipped with research grade, Zeiss optical microscopes capable of :

  • Transmitted plane and cross polarised light
  • Reflected illumination (for investigation of reflective minerals)
  • Epifluorescence microscopy

All the microscopes are equiped with digital cameras (with live view imaging on attached PC’s), and we have stepping stages (but driven using our own, in-house, software) that we use for modal analysis and acquisition of images for preparation of digital thin-sections and deep zoom images.

Textural Analysis

What is it and why might you need it ? 

Textural Analysis provides basic data on sandstone grain size, which almost invariably exerts some degree of control on final reservoir quality (either directly, or indirectly depending upon the degree of diagenetic overprinting).   The grain size data is also useful for calibration of core grain size in heavily cemented sediments, where original grain size is not always easy to determine in core, and cannot be measured accurately using bulk approaches (e.g. seive analysis or laser particle sizing).

We provide the raw data, as well as summary statistics including averages, sorting and other measures of spread and skew – including systematic grain size classification (in ½Φ bins).

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Petrographical Descriptions

We offer sample descriptions at a range of level of detail, from summary descriptions focussed on a specific set of feature(s) in a sample or sample set, up to completely-comprehensive characterisation of all aspects of the sample.

SEM Image showing clays on a grain surface, associated with quartz overgrowths and pyrite euhedra.
SEM Image showing clays on a grain surface, associated with quartz overgrowths and pyrite euhedra.

Most of the descriptive work is carried out using optical (plane-polarised light) light microscopy.  However, additional detail will usually be added using scanning electron microscopy and other microscopy methods as required.   Any additional micrcoscopy observations are incorporated directly into the sample descriptions (and not presented as separate descriptions).

There is always a temptation to “scrimp-and-save” a little on this aspect of petrographical studies, but this is the time where the real detail and intricacies of samples can be investigated and documented.

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Modal Analysis

What is it and why would you need it ? 

Modal analysis (point counting) data provides fundamental information on the composition of your samples, including:

  • Original detrital mineralogy.
  • Authigenic mineralogy.
  • Nature and abundances of macropores.

Data / results are presented in spreadsheet format, integrated onto individual sample descriptions and used extensively throughout our reports on various plots and diagrams.   The phases differentiated during modal analysis are tailored on a project-by-project basis – and can be designed to be consistent with existing datasets for mature fields, or compliant with the inputs required for “Touchstone” modelling.

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Scanning Electron Microscope (SEM) Petrography

tile04 Scanning Electron Microscopy (SEM) can be carried out as a stand-alone service, or in support of other petrographical analyses / descriptions.  We can analyse a range of sample types including small rock chips (“stub” samples) and polished thin-sections, as well as other materials.

Our main uses for SEM imaging and analysis are:

  • Detailed characterisation of clay mineralogy and other microcrystalline components (and their associated microporosity)
  • Elucidation of paragenetic relationships
  • Investigation of zoning and chemical variability within cements.
  • Systematic / automated collection of images for pore image analysis
  • Preparation of petrographical montages for deep zoom imaging

Because we have Scanning Electron Microscope capabilities in-house, we can offer a rapid turnaround / hotshot analysis of samples.  (Many geological materials can be analysed with a minimum of preparation – the samples only need to be dry and, in the case of samples containing liquid hydrocarbons, light cleaning is also required ).

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