1.1. Introduction :The acidity or the alkalinity of the drilling fluid can be measured by the
Concentration of the hydrogen (H+) ion in the fluid, As for instance, if H+ is large
(1×10-1), then the (OH-) hydroxyl concentration is very low
(1×10-13), the solution is strongly acidic. If the (OH-) concentration is (1×10-1) Very
high then (H+) concentration is very low (1×10-13) then the solution is strongly
alkaline.
𝑃𝐻 = [𝐻 + ] × [𝑂𝐻 − ] = 10−14
The pH of a solution is the logarithm of the reciprocal of the (H+) concentration in
grams moles per liter, expresses as:
1
𝑃𝐻 = 𝑙𝑜𝑔 + = −𝑙𝑜𝑔[𝐻 + ]
[𝐻 ]
PH of liquids decreases by increasing the acidity (hydrogen ions).
Example:
If the solution is neutral then H+ and OH- concentrations is the same equal to (1 x
10-7):
1
𝑃𝐻 = 𝑙𝑜𝑔 [10−7 ] = −𝑙𝑜𝑔[10−7 ] = −(−7) = 7
Acidity
alkalinity
A solution in which [𝐻 + ]> [𝑂𝐻 − ] is called acidic.
And a solution in which [OH -] > [𝐻 + ] is called alkaline.
And a solution in which [OH -] =[𝐻 + ] is called neutral.
The pH of a mud seldom is below 7 and in most cases exists between 8 and
12.5 depending upon the type of mud, the pH is important because the
PH affects.
1.2. Hydrogen ions concentration in fluids:pH:
The term pH is used to express the concentration of hydrogen ions in an aqueous
solution. pH is defined by:
pH= -Log [H+]
Where [H+] is the hydrogen ion concentration in moles per liter.
The pH of water is a measure of how acidic or alkaline the water is:
• On a scale of 1 to 14, normal fresh water has a pH of 7. If the water is acid,
the value is less than 7 and if it is alkaline the value is greater than 7.
• Bentonite will mix best if the pH of makeup water is adjusted to be between
8 and 9.
• Polymers too, perform best in makeup water with a pH in the range 7 to 9.
• pH will affect mud mixing, viscosity, water loss, hole stability and core
recovery.
fig(1): illustrate the pH scale
For this type of solution, the pH equals 7. Other combinations include:


The pH of (1-6) represents the minimum concentration of hydrogen ions.
The pH of (8-14) represents the maximum concentration of hydroxyl ions.
fig(2): illustrate the ranges of pH value
The pH of most water base drilling fluid systems : is maintained in the
(9 -10.5) range, and it’s determined either by the colorimetric method or the
Electrometric method. The colorimetric method utilizes chemically treated pH
hydrion paper which is placed on the mud's surface until a color change is noted. The
color observed is matched with a color chart on the side of the dispenser. If the salt
concentration is greater than 16,000ppm, pH paper is not recommended. The
electrometric procedure employs a pH meter with a glass electrode. Although more
accurate than pH hydrion paper it is quite sensitive to shock and difficult to maintain
under field conditions.
1.3. PH definition:Defined as the negative logarithm (to the power of 10) of the hydrogen –ions
concentration.
PH unit decrease with increasing the acidity by factor of 10.
pH= -Log [H+]
1.4. PH Measurements:1- PH meter.
2- PH strip.
1.5. Test instruments & Materials:1. The pH Paper:
Description:
The pH paper strips have dyes absorbed into the paper display certain colors in certain
pH ranges. It is useful, inexpensive method to
determine pH in fresh water muds. The main
disadvantage is that high concentrations of salts
(10,000 ppm chloride) will alter the color change
and cause inaccuracy.
Fig(3): pH-paper strips.
Fig(4): pH-paper strips.
2. The pH Meter:
Description:
The pH meter (or Benchtop meter) is an
electric device utilizing glass electrodes to
measure a potential difference and indicate
directly by dial reading the pH of the sample.
The pH meter is the most accurate method of
measuring pH.
Fig(5):pH-meter.
1.6. Test Procedures:The PH-Paper:
 Step1: Take the pre-mix mud sample and measure it’s rheological properties.
 Step2: Place the strip indicator in the mud and allow it to remain until the
surface of the paper is wetted with liquid and the color has been stabilized.
 Step3: Compare the color of the upper side of the Strip with the standard
colors provided with the test strip and estimate the mud PH.
 Step4: Add 1gm of caustic soda to the mud.
 Step5: Repeat steps 2 to 3.
 Step6: Add 2gm of caustic soda to the mud.
1.7. Tabulated Test Results & Calculation:Mud Property
PV
Pre-mix
mud
7
Mud+1gm
NaOh
4
Mud+2gm
NaOh
5
YP
15
16
30
PH
9
12
13
1.8. Comments:1. Plastic viscosity increase and deareaye with time by add NaoH.
2. Yeild point increase by add NaoH.
3. PH increase by add NaoH.
Fig (5): Relationship between Caustic soda , YP and pH.
30
25
20
PV
15
YP
10
PH
5
0
NaOh
NaOh
mud
Mud+2gm
Mud+1gm
Pre-mix
Fig(5).
1.9. Discussion – Results:Caustic soda causes increase in the pH of the mud (drilling fluid), where caustic soda
(NaOH) conceder a source of [OH+].So the results show the reading of PH increases
by increase the amount of caustic soda (NaOH) or sodium hydroxide added to the
mud sample.
1.10. Conclusion : pH is one of important factors which is affect on the drilling fluid and drilling
process.
 We should be measure and control pH for the mud to prevent drill string
corrosion and stability of mud system.
 Caustic soda is causes increase the pH of the mud (drilling fluid), where caustic
soda (NaOH) conceder a source of [OH+].
 The best and get the maximum benefit of the mud additive at pH range (910.5).
2. Answer these questions:1. Why it is important to control the pH of the drilling fluids?
Because of the following reasons:
1.To prevent drill string corrosion. corrosion rates can be reduced at
higher pH
levels and bacterial action on organic materials is retarded at elevated alkalinity
levels.
2.To get the maximum benefit at the mud additive at PH range (9-10.5), Organic
dispersants and filtration control agents generally achieve maximum effectiveness in
an alkaline environment.
3.Adverse effects of contaminating electrolytes are usually minimized at higher PH
levels.
4.By controlling pH of the mud. We can control the stability of different
mud
system, such as(Ligno-sulphaide system) may be improved at a pH of 10.0 or above.
5.To insure the solubility of gases (Co2, H2S).
6.To increase the polymer efficiency.
2. At what base range of PH the mud should be adjust?
(9-10.5)
 To preren steal corossian
 Potumes CNC; LV, HV, permalos, …..etc, works in hig pefermana at PH
range (9-10.5)PH.
 Mud is strong indecation for H2S formation.
3. References:1. Web site: http://en.wikipedia.org/wiki/PH.
2. Pictures on this report are from: www.Google.com
3. Last reports on this experiment.