Electrical properties system at ambient

1. Department Of Engineering
Faculty Of Petroleum Engineering
Reservoir Rock Properties Laboratory
PENG211L
Electrical Properties System
At Ambient
Submitted to :
Mr. Jamil Mahfoud.
Submitted by:
Bassam El Ghoul
May 15, 2018

2. ii
Contents
Chapter 1 Introduction................................................................................................1
1.1.Definition ...............................................................................................1
1.2.Objective………………………………………………………………1
Chapter 2 Apparatus ...................................................................................................2
Chapter 3 Other Equipment Used..............................................................................3
Chapter 4 Procedure....................................................................................................6
Chapter 5 Calculation..................................................................................................7
Chapter 6 Results and Discussion ..............................................................................9
Chapter 7 Error and Recommendations .................................................................11
Chapter 8 Conclusion ................................................................................................12
Chapter 9 References.................................................................................................13

3. iii
List of Figures
Figure 2.1 EPSA .............................................................................................................2
Figure 2.2 ScreenMonitor..............................................................................................2
Figure 3.1 Core Plug Saturator……………………………………………………………...3
Figure 3.2 Balance ..........................................................................................................3
Figure 3.3 Conductivity Meter........................................................................................3
Figure 3.4 Air Tank........................................................................................................ 3
Figure 3.5 Vacuum Dryer and Heater………………………………………………………4
Figure 3.6 Glass Microfibers...........................................................................................4
Figure 3.7 Silurian Core……………………………………………………………..……….4
Figure 3.8 Torrey Core………………………………………………………………………4
Figure 3.9 Indiana Core..................................................................................................4
Figure 3.10 Caliper…………………………………………………………………………...4
Figure 3.10 Becker……………………………………………………………………………4
Figure 3.11 Distilled Water.............................................................................................4

4. iv
List of Tables
Table 5.1 Cores Weights .................................................................................................7
Table 5.2 Cores Resistance.............................................................................................. 7
Table 6.1 Dimensional Results ........................................................................................ 9
Table 6.2 Resistivity at 25°C........................................................................................... 9
Table 6.2 Resistivity at 20°C........................................................................................... 9

5. 1
Chapter 1 Introduction
1.1. Definition
Rocks are formed from solid grain and pore space between these grains. These pores
are usually occupied by fluids water, oil or gas. These components have different
electrical properties, which mean different ability to conduct electrical current. For
instance, all grains except of some clay minerals, oil and gas is nonconductor. However,
brine water is conductor due to the ionic movement (Dandekar, 2013). Measuring the
resistivity of well formation was first discovered by Schlumberger brothers, and was
considered as the first commercial method of well logging (Schon, 2011). The concept
of electrical resistivity was first developed by Archie in the 1942, called Archie’s
equation. The resistivity of a rock mainly depends on the pore geometry, fluid filling
these pores, fluid saturation, temperature and salinity (Dandekar, 2013). From this test,
we can find several petrophysical properties that can give us a better understanding of
the reservoir. These factors are mainly: formation factor, tortuosity, cementation factor,
and resistivity index.
Beside of well logging, the resistivity test can be determined in the lab on core sample
at ambient conditions (atmospheric pressure, 20 degree Celsius) (Mahfoud, 2018). The
test is simply run by passing an electric current from one end of the core sample, and
measuring the flowing current and voltage drop between the two ends of the sample.
1.2. Objective
The objective of this experiment is to find the electrical resistivity of a sample and use
it, in finding different other parameter, like formation factor, tortuosity, cementation
factor, and resistivity index.

6. 2
Chapter 2 Apparatus
The EPS A is an instrument that we use to determine the resistivity of rock and brine
water in fully or partially saturated cores. The results that appear on the screen can
have used to determine the formation factor, cementation exponent m, resistivity
index and Archie saturation exponent n. The core hanged by pressing the core using
air with two platens. Then two electrodes clamped to the circumference of the core.
The whole apparatus is covered by a plastic box, to isolate sample from external
environment ("Electrical properties system @ ambient conditions", 2016).
Figure 2.1 EPSA
Figure 2.2 Screen Monitor
Electrodes
Electrode Plates
Pressure
Reader
Regulator
Power
Switch
Lid
Core Seat
Piston

7. 3
Chapter 3 Other Equipment Used
Figure 3.1 Core Plug Saturator Figure 3.2 Balance
Figure 3.4 Air TankFigure 3.3 Conductivity Meter

8. 4
Figure 3.7 Silurian Core Figure 3.8 Torrey Core Figure 3.9 Indiana Core
Figure 3.10 Caliper Figure 3.10 Becker Figure 3.11 Distilled Water
Figure 3.5 Vacuum Dryer and Heater Figure 3.6 Glass Microfibers

9. 5
Figure 3.1: Core plug saturator used to saturate the cores
Figure 3.2: Balance to weigh the cores
Figure 3.3 Conductivity meter to measure the conductivity of brine solution
Figure 3.4: Air Tank: used to push hold the sample between the two plates
Figure 3.5: Vacuum Dryer and heater: to de-saturate the cores
Figure 3.6: Glass Microfibers or pads: to stich the sample to the plates
Figure 3.7, 3.8 & 3.9: cores sample
Figure 3.10: Caliper: to measure the dimensions of the cores
Figure 3.11: Becker
Figure 3.12: Distilled Water to rinse the cores.

10. 6
Chapter 4 Procedure
1. Weigh the three core dry and record their weight.
2. Measure the dimensions of the core using the caliper, diameter and length and
record them.
3. Saturate the cores using the core plug saturator, and give them enough time to
be fully saturated.
4. Open the air tank valve
5. After removing them from the saturator, roll it over a paper towel to remove
surface brine.
6. After that, weigh the fully saturated weight of the cores and note them down
7. Measure the conductivity of the brine solution using the conductivity Meter.
8. Wet two pads with the brine solution
9. Stick the two pads to the plates
10. Load the sample on the sample seat, and open the air supply cylinder.
11. Turn the switch on, to let the air push the plate and hold the sample
12. Put the electrode on the sample
13. Close the lid over the sample to prevent liquid evaporation
14. Read the resistance of the core on the screen monitor
15. Remove the samples from the apparatus and then put them in the vacuum
dryer and heater and keep them 5 to 10 minutes.
16. After that, reweigh them, re-measure the resistance of the cores by repeating
from step 9 to 13, and note them down.
17. Put the three samples in a beaker and rinse them with distilled water, in order
to remove any salt deposal.
18. Then, replace them in the vacuum dryer and heater, and return the core to their
place.

11. 7
Chapter 5 Calculation
Table 5.1 Cores Weights
Indiana Torrey Silurian
Dry weight (g) 56.9470 58.6485 64.864
Fully Saturated weight (g) 63.82 65.64 70.15
Desaturated Weight (g) 60.85 62.68 67.15
Diameter D (cm) 2.5 2.5 2.5
Length L(cm) 5 5 5
Table 5.2 Cores Resistance
Indiana Torrey Silurian
Fully Saturated Resistance r (ohm) 558 262 3140
Partially Saturated Resistance r (ohm) 566 251 1930
The conductivity for Brine water is 55.2 ms/cm=5520 ms/m
At 25°C 𝑅𝑒𝑠𝑖𝑠𝑡𝑖𝑣𝑖𝑡𝑦 = 𝑅𝑤 =
1
K
=
1
5520𝑚𝑠/𝑚
= 0.18116 𝑜ℎ𝑚 𝑚
At 20°C R=Rref (1+α (T-Tref) => Ref = R / (1+α (T-Tref)
= 1.18116 / (1+0.0214(25-20)) = 0.1636 ohm.m
These Examples are done on the Indiana Core
Area of the core= 𝐴 =
𝜋
4
𝐷2
=
𝜋
4
(2.5 × 10−2
)2
= 0.000491 𝑚2
Bulk Volume = 𝑉𝑏 = 𝐴 ∗ 𝐿 = 0.000491 × (5 × 10−2) = 2.454 × 10−5
𝑚3
Pore Volume =𝑉𝑃 =
Wwater
⍴
=
WSaturated −Wdry
⍴
= 6.738 𝑐𝑚3
= 6.738 × 10−6
𝑚3

12. 8
Porosity= ∅ =
𝑉𝑝
𝑉𝑏
=
6.738×10 −6
2.454×10 −5 × 100 = 27.45%
Fully Saturated Resistivity = Ro= Resistance *Area/ Length
= r A/L = 558*0.00049/0.05=5.47 ohm.m
Partially Saturated Resistivity = Rs= Resistance *Area/ Length
= r A/L = 566*0.00049/0.05=5.55 ohm.m
Converting the resistivity form 25°C to 20°C
R=Rref (1+α (T-Tref) => Ref = R / (1+α (T-Tref)
= 5.47 / (1+0.0214(25-20)) = 4.948 ohm.m
Formation Factor = Fr = Ro/Rw = 4.94/0.1636= 30.2394
Cementing Exponent m = - ln(Fr)/ln(∅)= -ln (30.2394)/ln(0.2745)= 2.637
Tortuosity = T = ∅. Fr = 0.2745 * 30.2394 = 8.302
Resistivity Index = RI= Partially Saturated Resistivity/Fully Saturated Resistivity
=5.019/4.948 = 1.014
Saturation= Sw= ((partially saturated weight – dry weight)/brine density)/pore volume
=((60.85-56.947)/1.02)/6.738)=56.78%

13. 9
Chapter 6 Results and Discussion
Table 6.1 Dimensional Results
Area m2 V b *10-5 m3 vp *10^-6 m3 Porosity (%)
Indiana 0.000491 2.454 6.738 27.454
Torrey 0.000491 2.454 6.854 27.927
Silurian 0.000491 2.454 5.182 21.115
Table 6.2 Resistivity at 25°C
Column1 Ro (Ω.m) Rt ( Ω.m)
Indiana 5.478 5.557
Torrey 2.572 2.464
Silurian 30.827 18.948
Table 6.3 Resistivity at 20°C
Ro (Ω.m) Rt ( Ω.m) Sw (%) Fr m t RI
Indiana 4.95 5.02 56.79 30.239 2.637 8.302 1.014
Torrey 2.32 2.23 57.66 14.198 2.080 3.965 0.958
Silurian 27.85 17.12 43.25 170.164 3.303 35.930 0.615
Table 6.1 shows the dimensional results for each rock sample, like area, bulk volume,
pore volume and porosity. The three core with the same diameter and length have the
same area and bulk volume, but in terms of pore volume and porosity, the Torrey has
the highest porosity and the Silurian has the lowest one.
Table 6.3, shows the electrical properties of the cores at 20°C, like the resistivity of the
core when both partially and fully saturated, the formation factor, etc…
The resistivity of the water is very small comparing to the cores resistivity that is why
the resistivity of cores decreases as the brine saturation increases. As the pore space is
filled with brine water, the resistivity decreases as the porosity increases, and vice versa.
That is illustrated in the idea that the Silurian that have the higher resistivity in both
fully and partially saturated, in contrast of the Torrey which has the lowest resistivity.

14. 10
In the other hand, the resistivity of cores should increases as the brine saturation
increase, but this was shown only in the Indiana core, and not in the two other core.
Other main factor affecting the resistivity is the temperature. Where the general rule is
that, the resistivity increases with increasing temperature for conductor material and
decrease with increasing temperature for isolator material (Gray, 2018). In this
experiment, we are dealing with the brine water, which is a conductor material, which
explain the decrease in resistivity as converting from 25°C to 20°C.
The cementing exponent m, is related to the degree of cementing of the core (Mahfoud,
2018). The Torrey showed an m exponent between 1.8 and 2.2, which referred to be
consolidated, and the two other cores Silurian and Indiana showed an m value above
2.2, which is referred to highly, consolidated.
The tortuosity is the length taken by the fluid over its length. As the resistivity increases
the tortuosity increases, that is illustrated by the fact that the Silurian has the highest
values for both resistivity and tortuosity.
The resistivity index is a ratio of dry and fully saturated resistivity. These values should
be higher than one due to the principle discussed earlier about the increase in the
resistivity by the decrease of brine saturation. However, due to the data calculated only
the Indiana showed the right answer.

15. 11
Chapter 7 Error and Recommendations
This experiment was subjected to some errors, which can be illustrated multiple
times in the experiment.
First, all measurements taken can be subjected to human errors, like the diameter and
length and weights of cores, to the conductivity and resistance of both brine and cores.
Second, the error can also be during the saturation of cores, while conducting the core
plug saturator, where this error can lead to an uncompleted saturation for cores, and
errors in measuring cores porosities.
Third, the time needed for weighing the cores after removing them from the saturator,
can to cause some water vaporization, which will affect the R0 of the cores.
Forth, the cores can be unseated perfectly, which can change the area of contact between
the electrode and the core, leading to wrong readings. In addition, not giving the cores
enough time for reading there resistance can also lead to wrong readings.
Bring it all together; any of the error mentioned above can be the cause in the error that
we faced in the decrease in the resistivity of Silurian and Torrey core after we de-
saturated them. On the other hand, it can be due to the deposition of salt grain in the
water after heating, which increases the salt concentration in the brine reminding in the
core, decreasing its resistivity.
Avoiding these errors is the major key to have very accurate results out of our
experiment, and repeating it multiple time can increase our precision.
In addition, giving enough time for cleaning and measuring is highly recommended to
improve our results.

16. 12
Chapter 8 Conclusion
In conclusion, the EPS is an experiment conducted to measure the physical,
lithological and electrical properties of rocks samples by measuring their resistance.
Based on our results, we concluded that the resistivity of cores is inversely
proportional to the saturation, as the saturation increases the resistivity decreases. This
inversely proportional correlation is also between the resistivity and the porosity of the
core sample.
The experiment was subjected to a major error in the resistance of two cores when
partially saturated, where it is illustrated in the wrong data obtained after our
calculations.
It is recommended to avoid the human error in while conducting the experiment,
and repeat it multiple time to improve our results. In addition to calibrating the EPS and
giving enough time for each reading.

17. 13
Chapter 9 References
"Electrical properties system @ ambient conditions". (2016). Retrieved from vinci-
technologies: http://www.vinci-technologies.com/products-
explo.aspx?IDR=82292&idr2=82548&IDM=536812
Dandekar, A. Y. (2013). Petroleum Reservoir Rock and Fluid Properties (2nd ed.).
USA: Taylor & Francis Group,.
Gray, S. (2018). The Physics Hypertextbook . Retrieved from physics.info:
https://physics.info/electric-resistance/
Mahfoud, J. (2018, April 24). EPS Theory. Retrieved from PENG211L LAB 1
Reservoir Rock Properties Laboratory-SPRING 2017:
https://lms.pu.edu.lb/sites/12017SPRING6022/Documents/Forms/AllItems.as
px
Schon, J. (2011). Handbook of Petroleum Exploration and Production. In J. CUBITT
(Ed.), Physical Properties of Rocks a workbook (Vol. 8, p. 276). Oxford, UK:
Elsevier.