The Volume of Clay computation using Gyllenhammar formula
The computation process was adapted in analogy with Vclay computation from Neutron-Density cross plot, where instead of Neutron log, the P-wave velocity can be used. That gives a possibility to estimate «clean» clays and sands but does not provide good separation for clay-sand mixture (or other minerals). Thus, to increase accuracy, we should apply this formular to each formation separately, adjusting the C point. The Gyllenhammar approach for volume of clay computation is shown on the picture below.
In it important to use non-linked P-wave velocity (Vp) and Density, that Rune Inversion algorithm provides.
where VclSD* is a volume of clay computed from the inverted P-wave (Son) and Density (Den)
DenCl1 2.65 g/cc
DenCl2 2.05 g/cc
SonCl1 55 us/ft
Soncl2 104 us/ft
SonClay 150 us/ft
DenClay is the only variable here changing with depth.
*to recomputed by formation, the right chart Density-Sonic logs must be constructed from the well logs of P-wave and Density and the most suitable C point (DenClay) should be chosen and C point varies from 1.8 g/cc up to 2.58 g/cc.
For more details regarding the theory for a volume of clay computation from P-wave and Density, refer to
Gyllenhammar, C.F. . Calculating a synthetic density curve using a volume of clay and velocity. First Break, 38 (6), 45–49. https://doi.org/10.3997/1365-2397.fb2020041