Pet 524

Porosity Measurement
V V V b g p
Measurement of any two of the three volumes allows for the determination of porosity

Porosity Measurement
Bulk Volume
a. linear measurements

4 cm

10cm

V  r h b

2

Porosity Measurement
Bulk Volume
b. displacement method gravimetrically fluid displaced by sample measured volumetrically or

Prevent fluid penetration into pore space by:i. coating the rock with paraffin ii. saturating the rock with the fluid into which it is immersed iii. using mercury Gravimetric methods observe the loss in weight of the sample when immersed in afluid, or observe the change in weight of a pycnometer filled with mercury and filled with Hg and sample. Volumetric methods measure the change in volume when the sample is immersed.

PorosityMeasurement
Bulk Volume
Example – displacement method

Weight of saturated sample immersed in water

Weight dry
Wwet = 12.6 gms Wdry = 20 gms

Weight of water displaced Wwtr = Wsat - Wwet= 9.9 gmsBulk volume Vb = Wwtr/rwtr = 9.9 cc

Weight saturated

Wsat = 22.5 gms

Porosity Measurement
Grain Volume
a. Direct methods i. Dry weight of sample/density of matrix = Vg ii. Destructivemethods (Melcher-Nutting or Russell) - requires sample to be crushed - Vg determined gravimetrically by principle of bouyancy. - not very accurate! b. Gas Expansion methods • Boyle’s Law porosimeter •non-destructive, reasonably accurate

Porosity Measurement
Boyle’s porosimeter
 The total moles of gas is constant, thus

n n n t 1 2
 Substituting the ideal gas equation,

p V pV p V f f 11 2 2 RT RT RT
 Isothermal conditions prevail,

p V pV p V f f 11 2 2
 Substituting for the volumes,

p (V  V  V )  p (V  V )  p V f 1 2 g 1 1 g 2 2
 Rearranging results in anexpression for grain volume

V  g

V (p  p ) V ( p  p ) 1 f 1 2 f 2 p f  p1

(2.16)

where V1 and V2 are the calibrated chamber volumes.

Porosity Measurement
Boyle’s porosimeter -...