IP Advanced - Clay and Shale

IP Advanced Training

Paul Spooner IP Product Champion

Clay and Shale What’s What’ s the difference & why is it important?

LIFTING THE FOG OF CONFUSION SURROUNDING CLAY AND SHALE IN PETROPHYSICS Paul Spooner, Senergy SPWLA 55th Annual Logging Symposium, May 18-22, 2014, paper VV

• Shale is a rock, typically defined as an indurated, finely laminated, sedimentary rock, composed primarily of clay, mud and silt. • This definition does not describe the mineralogy but the grain size. • In this definition, clay refers to clay sized particles, i.e. < 1/256 mm. • Whilst clay can refer to grain size it can also refer to clay minerals, and it is the dual meaning of the word clay that is at the heart of the confusion in the industry. • Clay minerals are a group of hydrous aluminium silicates with a sheet-like structure (phyllosilicates), which adsorb water on their surfaces. • In shale, most of the clay sized particles are composed of clay minerals.















Phi/Sw Vshale workflow

•IP has always explicitly been a Vclay program, but some users prefer to work with Vshale. •This workflow allows Vshale users to work the way they want. •It will also clarify the difference between clay and shale. •In the Vclay module the ‘Calculate Shale Volume’ option changes the default output curve names and all the labels for for curves and parameters.


•In PhiSw the user defines whether the input curve is Vclay or a Vshale, there are new parameters and a new output curve ‘Vshale’. •When creating a PhiSw parameter set for the first time it is sensitive to the ‘Calculate Shale Volume’ in Vclay Vclay..


•In the Vclay module the user makes Wet Shale picks and outputs VSH curves.


•In PhiSw there are parameters and interactive picks for both Wet Shale and Wet Clay •CSR (Clay Shale Ratio) converts between Vshale and Vclay. •CSR is % of clay in the shale i.e. CSR = Vclay/Vshale •Log Plot shows Vshale


•In the Shaley-Sand trend the computed porosity is exactly the same regardless of whether you use a Vshale or a Vclay workflow •However, in the Shale trend the effective porosity will be too high as Vclay will be too low,, unless you make CSR a variable curve low •It may be easier to pick the Shale Point •....but you still have to ‘pick’ CSR •... and it is clay that matters

Vsilt Index

•For a given volume of clay we expect the resultant Phie to be within a certain range. •If the porosity is lower than this then something else must be reducing it. •This is what the VSILT index represents. •It indicates that the porosity is lower than expected given the Vclay.. This could be cement silt Vclay or whatever. •It is purely for display purposes and does not impact on porosity or Sw calculations.

Limits and Bad Hole

•The effective porosity must be less than the porosity limit line. •Phi Max is set to the maximum porosity in silt free sand. It is used to calculate the silt index. Delta Phi Max is then adjusted to remove unrealistic porosities. •Vcl cutoff removes porosity in shales. It is useful for cleaning up an interpretation. •Vcl cutoff can also be used to boost the Archie ‘m’ parameter in shales, which removes unlikely hydrocarbon saturations in shales.

Phi/Sw – Phi/Sw – Grain Grain Density

• A A Grain Density curve can now be be output, for plotting against core Grain Density data as a QC.

•RHOMA output curve is a clay corrected, clean matrix density. •RHOMA may not match the core data very well as it is the whole rock, including the clays as well. •GrainDen should match core better •In clean rocks RHOMA = GrainDen

IP Advanced - Clay and Shale

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