## Permeability

## Permeability

(OP)

Hi - I am looking for typical hydraulic conductivity values for shales in Texas and still looking for a convincing range. I would appreciate your feedback if you may have used it for GeoStudio analysis.

Also for the sake of argument let's assume two laboratory tests showed K1= 1E-5 m/sec and K2=1E-6 m/sec values. If one wants to use an average of the two, would it be a geometric or an arithmetic average. I.e., is the average of the two tests SQRT(K1*K2) or K1+K2)/2? Thank you.

Also for the sake of argument let's assume two laboratory tests showed K1= 1E-5 m/sec and K2=1E-6 m/sec values. If one wants to use an average of the two, would it be a geometric or an arithmetic average. I.e., is the average of the two tests SQRT(K1*K2) or K1+K2)/2? Thank you.

## RE: Permeability

But regarding choosing a design value based on a data set, I can say there is no one correct method. You can choose arithmetic average, geometric average, harmonic average. Then you can take the average of the averages, you can just adopt the lowest value, you can calculate a 95% confidence value based on statistics....shall I keep going.

This is where engineering judgement comes in to play. For your specific case of 1.5 or 1.6, I would pick the more conservative value since they are so close.

## RE: Permeability

I guess by harmonic you meant K = L/(Ll/k1 + L2/k2), where L = L1+ L2. Then may be I take the average of arithmetic (parallel) and harmonic (series). I leave out the geometric mean as cannot yet be convinced why to employ it. In term of adopting the lowest values, will it be usually a conservative approach?

## RE: Permeability

Of course not, it depends, if youre doing infiltration calculations then 1.5 is more conservative, if you are doing dewatering then 1.6 is more conservative.

## RE: Permeability

## RE: Permeability

literature survey suggested K in the range of 1E-9 to 1E-14 ft/sec for shales. Again uncertain what average value one can take as the arithmetic average always errs on the upper level.

## RE: Permeability

Scale effects can be significant.

An SPT in a machine augere hole is a pretty poor-quality undisturbed sample...and what if you have joints at a multi-meter spacing that are significant relative to the work you are doing but you drilled a borehole in a way to miss a bunch of them? I.e. in between joints and the machine borehole smeared it all up and the SPT missed the joints.

## RE: Permeability