## Porosity Measurement by Digital Helium Porosimeter

Porosity fraction is defined as the ratio of the pore volume to the bulk volume of the rock

sample:

ππππ ππππ’ππ

π =

π΅π’ππ ππππ’ππ

In lay terms, pore volume is the void space in the rock. Bulk volume is the volume that the rock

occupies, sometimes called matrix volume. Grain volume is the volume of the rock grains or

solids (not including the pore volume). Porosity is the fraction of void space in the total rock.

Thus, pore volume can be calculated from the bulk volume and grain volume measurements.

ππππ ππππ’ππ = π΅π’ππ ππππ’ππ βπΊππππ ππππ’ππ

Bulk volume is usually determined by callipering or by displacement. Porosity can be calculated

from the equation:

π΅π’ππ ππππ’ππ βπΊππππ ππππ’ππ

π =

π΅π’ππ ππππ’ππ

First, find the line Volume (VL) and the cup volume (Vcup) for at least 5 different random disks

set collection.

Use the following equation to find VL and Vcup after a linear curve fitting:

ππΆπ’π + (1 β

π1

π2

) ππΏ = βππ·βπ ππ‘

Grain volume can be determined using the following equation:

ππ = ππΆπ’π + (1 β

π1

π2

)ππΏ β βππ·βππ ππ

Procedure:

1. Place the core plug in the Matrix Cup.

2. Turn Valve βSAMPLE VALVEβ to the βVENTβ position.

3. Open Valve βGAS INLETβ to βON.β

4. Pressurize the system to approximately 100 psi.

5. Adjust the pressure by rotating the handle of the βREGULATOR.β

6. Close βGAS INLETβ (βOFFβ Position).

7. Record βUPSTREAM PRESSUREβ, P1.

8. Turn βSAMPLE VALVEβ to βEXPAND,β directing the helium into the cup.

9. Observe the βUPSTREAM PRESSUREβ until a stable reading is obtained.

10. Record the stabilized pressure reading, P2.

Results:

1. Calculate line volume (VL) and cup volume (Vcup)

2. Calculate grain volume and porosity of your samples

Questions:

1. Is the porosity measured in Exp. 3 consistent with porosity measurement from Exp.2?

Which experiment shows higher values? Is it for both samples A and B? Explain the

possible reasons of differences in porosities from Exp.2 and Exp.3.

2. Rock (formation) compressibility is a crucial property fluid flow calculations and studies

which can be measured in the lab. What is the mathematical relationship (formula) between

porosity and formation compressibility? Also how the rock compressibility can be measured

in the lab (explain in one paragraph).

Disk Set B-409

Disk # Disk Size, in. Disk Volume, cc

1 β
1.59864

2 β
4.80933

3 Β½ 6.41134

4 ΒΎ 9.63592

5 1ΒΌ 16.09359