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Calculate Water Saturation From Well Logs

F = Formation Factor

F = c ÷ ( por ^ m )

c = cementation factor
m = cementation exponent
F = 1 ÷ ( por ^ 2 ) (for limestones)
F = 0.81 ÷ ( por ^ 2 ) or 0.62 ÷ ( por ^ 2.15 ) (for sands)

Sw = Water Saturation
Sw = ( F * Rw ÷ Rt ) ^ 1/n
n = saturation exponent
Sw = [ ( c * Rw ) ÷ ( por^m * Rt ) ] ^ 1/n


Constants

c

= cementation factor (1)

m

= cementation exponent (1.8)

n

= saturation exponent (1.8)

Formation Water Resistivity

Rw

= Water Resistivity, ohm-m

Tm

= Rw Measure Temperature, °F
R2 = R1 * (T1 + 6.77) / (T2 + 6.77)

Temperature at Zone Depth (BHT)

BHT

= Bottom Hole Temperature, °F

Depth

= feet

Temp Gradient

= °F per 100 feet (1.5)

Temp Surface

= °F, mean annual, (50°F)
BHT = ( depth * gradient ) + surface temp

Log Value - Deep Resistivity

Rt

= Resistivity, ohm-m

Log Value - Porosity (Choose one of three)

por

= % porosity

Delta T

= sonic travel time (µs/ft)

Tma

= matrix travel time (51.3 µs/ft)

Tf

= fluid travel time (188.7 µs/ft)
Sonic Porosity = ( Delta T - Tmatrix ) / ( Tfluid - Tmatrix )

rho b

= bulk density (grams/cc)

rho ma

= matrix density (2.65 grams/cc)

rho f

= fluid density (1.0 grams/cc)
Density Porosity = ( rho ma - rho b ) / ( rho ma - rho f )