4. A dry core sample has a weight of 420 g. This core sample is then saturated 100% with brine which has a density of 1.05 g/cm3. The weight of the saturated core sample is 450 g. The core sample is 10 cm long and has a diameter of 5 cm. What is the porosity of the core sample?
Porosity = Pore volume (Vp) / Bulk volume (VB)
Bulk volume is calculated by using the formula, VB = r2l
Where, r = radius of core sample = 5/2 = 2.5cm
and l = length of the core sample = 10cm
VB = r2l = 3.14 x 2.5 x 2.5 x 10 = 196.25 cm3
The pore volume of the core sample is calculated as:
Vp = Weight of saturated core - Weight of dried core / Specific gravity of brine
Specific gravity = density of any substance/Density of water
Density of water = 1g/cm3
Specific gravity of brine = 1.05/1 = 1.05
Vp = 450 - 420/1.05 = 28.57cm3
Porosity = 196.25/28.57 = 6.87
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