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:
π‘ƒπ‘œπ‘Ÿπ‘’ π‘‰π‘œπ‘™π‘’π‘šπ‘’
πœ™ =
π΅π‘’π‘™π‘˜ π‘‰π‘œπ‘™π‘’π‘šπ‘’
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.
π‘ƒπ‘œπ‘Ÿπ‘’ π‘‰π‘œπ‘™π‘’π‘šπ‘’ = π΅π‘’π‘™π‘˜ π‘‰π‘œπ‘™π‘’π‘šπ‘’ βˆ’πΊπ‘Ÿπ‘Žπ‘–π‘› π‘‰π‘œπ‘™π‘’π‘šπ‘’
Bulk volume is usually determined by callipering or by displacement. Porosity can be calculated
from the equation:
π΅π‘’π‘™π‘˜ π‘‰π‘œπ‘™π‘’π‘šπ‘’ βˆ’πΊπ‘Ÿπ‘Žπ‘–π‘› π‘‰π‘œπ‘™π‘’π‘šπ‘’
πœ™ =
π΅π‘’π‘™π‘˜ π‘‰π‘œπ‘™π‘’π‘šπ‘’
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:
𝑉𝐢𝑒𝑝 + (1 βˆ’
𝑝1
𝑝2
) 𝑉𝐿 = βˆ‘π‘‰π·βˆ’π‘ π‘’π‘‘
Grain volume can be determined using the following equation:
𝑉𝑔 = 𝑉𝐢𝑒𝑝 + (1 βˆ’
𝑝1
𝑝2
)𝑉𝐿 βˆ’ βˆ‘π‘‰π·βˆ’π‘ˆπ‘ π‘’π‘‘
Procedure:
1. Place the core plug in the Matrix Cup.
2. Turn Valve β€œSAMPLE VALVE” to the β€œVENT” position.
3. Open Valve β€œGAS INLET” to β€œON.”
4. Pressurize the system to approximately 100 psi.
5. Adjust the pressure by rotating the handle of the β€œREGULATOR.”
6. Close β€œGAS INLET” (β€œOFF” Position).
7. Record β€œUPSTREAM PRESSURE”, P1.
8. Turn β€œSAMPLE VALVE” to β€œEXPAND,” directing the helium into the cup.
9. Observe the β€œUPSTREAM PRESSURE” 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…œ 4.80933
3 Β½ 6.41134
4 ΒΎ 9.63592
5 1ΒΌ 16.09359

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