Petrographical and petrophysical analysis

Although very different in their approach and the scales on which they are undertaken, petrographical and petrophysical analyses complement our other analytical services by providing contextual information from scales smaller and larger to that resolvable in a borehole image or core.

Petrography

Task has an excellent relationship with a high quality thin sections provider. Our thin sections are resin impregnated, diamond lapped, dual stained for K-feldspar and carbonate, cover slipped and free of carborundum residue. We prefer to use core plug trims to allow direct integration with the core analysis results and typically we sample across the permeability distribution to allow more relevant analysis. We can also use core chips, side wall cores, junk-basket samples and ditch cuttings. Un-cleaned plug trims can bring benefit by preserving hydrocarbons within pores.

Thin section analysis

• Point counted to 200 points.
• Data entered into an Excel spreadsheet along with associated core analysis data.
• Granulometric data recorded as mean and maximum grain size and sorting.
• Grain types counted.
• All cement phases detailed and counted.
• All trace components logged.
• All porosity types counted.
• Pore types documented.
• Digital images gathered.
• Basic description provided.
• Microporosity content calculated.
• Samples classified.

Data analysis

• Porosity loss by compaction and cementation calculated.
• Summary statistics derived for all variables, presented on spreadsheets.
• Triangular compositional diagrams produced.
• Q:F:L calculated for each sample.
• Mean Q:F:L calculated.
• Cross correlation matrix derived between all variables, including depth, presented on spreadsheets.
• Cross plots between key variables derived and annotated.
• Derive controls on reservoir character.
• Multivariate statistical methods including multiple linear regression, cluster analysis and ordination techniques.

Results and data presentation

• Diagenetic succession detailed.
• Thin section described.
• Controls on reservoir quality determined.
• Results presented as an integrated report with text, figures, plates and data appendices.

Other techniques and services offered in conjunction with partners

• Scanning electron microscope analysis.
• Whole rock XRD.
• Clay phase XRD.
• Cathodoluminescence.
• Heavy mineral analysis.
• Isoptope analysis.

Petrophysics

Downhole images are acquired by utilising variation in petrophysical rock properties and the interpretation of the images relates them to a geological response. Any one image reflects only one property, e.g. resistivity in most cases. However, one petrophysical log cannot sufficiently describe the complexity of a rock and if possible, multiple logs responses are used to characterise e.g. lithologies, fractures, cementation or pore fill. For wells with no image log and little core information the geological interpretation of the petrophysical logs may be useful, applying the electrofacies concept. An electrofacies is defined by an individual set of log responses which define one lithology and each lithology has to differ from others by at least one parameter. Again, the greater the diversity of log measurements the better the characterisation and the less ambiguous the interpretation. The translation of log responses to a lithofacies is also influenced by well condition, porosity or lithification. Also, the nature of the log curve can indicate trends which may be related e.g. to fining upwards or coarsening upwards sequences or repetition due to faulting.

Petrophysical analysis

• Cross-plots
• Core-log integration
• Calculation of clay volume

Electrofacies analysis

• Characterisation of electrofacies by multi-log analysis
• Establish continuous electrofacies profile

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