Shaly Sand Sw

While the Archie equation is usually reasonable for "clean" or shale free formations, most fluvial/delatic sands are not completely shale free. If the presence of shale is not accounted for the calculated Sw will usually be higher than the true formation Sw. There are several good techniques available for estimating the effect of shale resistivity water saturation. The Simandoux water saturation equation is used here. It is fairly complex; however, it can be easily calculated using the Modified Simandoux Equation. NOTE: When the volume of clay is 0 this equation defaults to the Archie formula.

Sw=min((0.5*Rw/PHIE^m)*((4*PHIE^m)/(Rw*ILD)+(Vclay/Rshale)^2)^(1/n)-clay/Rshale), 1)

Calculating BVW Simandoux

The correct formula is:

BVW=PHIE*Sw

	DEPTH	PHIE	Vclay	ILD
A	11305	.009	.831	2.11
B	11333	.169	.076	24.36
C	11367	.141	.110	10.79
D	11381	.091	.180	6.24