The GR picks chosen are used for a first estimate when actual, measured, clay-volume data are available. Comparison of the XRD values with the GR-derived values indicated a clean value of 30 and a shale value of 101.

The clean value of 30 should be slightly lower than the pick from the log because these zones are not 100 percent sandstone. A recalculation of Vshale using the clean pick of 30 resulted in the following (use these values for subsequent exercise):

 

	DEPTH	Vclay (GRCL=30)
A	11305	0.831
B	11333	0.076
C	11367	0.110
D	11381	0.180

Note the relative values for each depth then proceed to the next step in the process.