1. NACE Corpus Christi, TX – Nace Section Meeting May 20, 2014
Oilfield Water Analysis:
What Does It all Mean?
Tom Pickthall
EnhanceCo, Inc.
NACE Corpus Christi, TX – Nace Section Meeting May 20, 2014

2. History API RP 45 committee started 1958 Published 1968
Latest version 1998
No current NACE Standard
APPLIED WATER TECHNOLOGY
by Dr. Charles Patton, Campbell Petroleum Services
Second Printing 1991
OIL FIELD WATER TECHNOLOGY
by Michael Davies and P.J.B. Scott
2006 NACE

4. What’s Important
pH, CO2, H2S, O2 and alkalinity must be run in the field for accuracy.
If possible, overfill sample container and seal to minimize loss of gasses.
Go ahead and splurge: use a new sample container, not an old Coke bottle.
Deliver samples to lab as fast as possible. Note field readings.

5. Must Have Field Kits 1. pH meter 2. Carbon Dioxide (CO2)
3. Hydrogen Sulfide (H2S)
4. Oxygen (O2)
5. Total Alkalinity
(available from HACH, Chemetrics, Calgon)

6. Results and What They Mean I
ppm, mg/L, me/L
ppm: weight/weight or volume/volume
Mg/L: weight per volume, used by API
ppm/Mg/L= with distilled water
me/L (milliequivalent/L): expression of chemical combining power of the electrolyte in a fluid; used to check balance of cations/anions
Water Patterns: used to compare various waters by constituents; see API form

7. Results and What They Mean IIpH
The single most important measurement
Acid Neutral Basic
Normal oilfield range = 6-8
Affected by CO2, H2S, Fe, bicarbonate, alkalinity
Changes in pH are logarithmic: pH 8 = 10 x pH 7

8. Results and What They Mean III
Cations +
Sodium (Na): 40 % of the Sodium Chloride (Brine) compound
Used to force balance the sum of cations and anions (TDS)
Calcium (Ca): part of the measure of the “hardness” of water; can lead to the formation of Calcium Carbonate or Calcium Sulfate scale.
Magnesium (Mg): another part of the total “hardness” of water; can contribute to formation of scale.

9. Results and What they Mean IV
Cations +
Barium (Ba): This is the “bad boy” of scale formation. Limited solubility in produced waters and insoluble in acid.
Iron (Fe): Either naturally occurring from formations or as the result of corrosion of steel. Separate acidized sample for analysis?
In sour (H2S) systems: Look for Manganese (Mn).

10. Scale Formation Calcium Carbonate (CaCO3):
Solubility depends on temperature, pressure and concentration of ions. Acid soluble.
Probability of scale formation increases with:
Increase in temperature
Partial Pressure of CO2 decreases
pH increases
Total pressure decreases as TDS decreases

11. Scale Formation Calcium Sulfate (CaSO4)
Not acid soluble but may be “converted”
Solubility depends on temperature, pressure, dissolved salts
Probability of scale formation increases with:
Increase in temperature
Increase in dissolved salts, up to 150F
Increase in pressure
pH has little effect on CaSO4

12. Scale Formation Barium Sulfate (BaSO4) Least soluble of all scales.
Scale likely to occur whenever both Ba and SO4 are present in a water.
Increases slightly with temperature
Increases slightly with dissolved salts
Increases slightly with pressure
pH, no effect on solubility

14. Results and What They Mean V
Anions
Chloride (Cl): 60% of the Sodium Chloride compound (NaCl, Brine). NaCl will be generally 80% of TDS.
Sulfate (SO4): Combines with Ba & Ca to form scales.
Carbonate (CO3): “P” Alkalinity found in water with pH above 8.3
Bicarbonate (HCO3): “M” Alkalinity in water with pH between 4.5 & Buffers corrosiveness of brine.

15. Results and What they Mean VI
Specific Gravity: The weight of a test sample compared to the weight of distilled water (1.0). TDS increases weight.
Resistivity: Resistance to electrical charge. The higher the resistivity the lower the salinity. Measured in ohm-meter.
Hydrogen Sulfide (H2S): Acid gas contributes to corrosion.
Carbon Dioxide (CO2): Acid gas contributes to corrosion.
Oxygen (O2): Most corrosive of gasses in produced water.

18. Corrosion
Corrosion in oilfield water is caused by one of the following constituents:
Oxygen (O2):, does not affect pH; deep pits caused by Cathodic Depolarization
Carbon Dioxide (CO2): Partial Pressure important; Mesa type attack.
Hydrogen Sulfide (H2S): affects pH, shallow pits; creates FeS (black water/solids).
Bacteria: Localized pitting caused by low pH (<3); not part of API water analysis but very important to corrosion process.

19. Conclusion
API water analysis very useful tool but you need to understand what it is telling you.
pH: high or low i.e. scale or corrosion
Brine level: 20,000 Cl (low), 80,000 Cl (high). How will this affect scale/corrosion?
Am I forming scale? (Ba, Ca, SO4, CO3) Is it acid soluble? What temperature? What pressure?
Do I have corrosion? pH, Bicarbonate, FeS?
Is this water significantly different than last time? (water pattern)
How will water analysis affect bacteria analysis? (Cl, TDS, O2, H2S)