Predicting Clay Content And Poroszty From Gamma-Ray And Conductivity Logs

As the first step in predicting flow properties from geophysical logs, a gamma-ray<br>log was used to predict clay volume fraction (& 0.021), and the conductivity log was used<br>to predict porosity fraction (& 0.029) in the Oak Ridges Moraine (ORM) complex,<br>Ontario. First, empirical relations between the gamma-ray count and lab-measured clay<br>volume were derived and used to predict clay volume throughout the entire well for five<br>different lithologies. Then, Archie’s Law was used with a clay correction to calculate<br>formation factor. Finally, relations between lab-measured porosity and predicted<br>formation factor were derived and used to predict porosity throughout the entire well for<br>each lithology.<br>In the Aurora well, we reasonably predicted the volume fraction of clay and<br>porosity, and were able to identify known aquifer and aquitard units using the computed<br>formation resistivity factor. The porosity and formation factor pseudo-logs may be used<br>to model permeability at the well. The derived cementation factors were: m = 1.6 in the<br>sands, silts and gravels; m = 1.8 in the silt/clay rythmite series; and m = 1.3 in the poorly<br>sorted, clayey silt tills.