May 20, 2014 - NACE Corpus Christi Section
Transcript May 20, 2014 - NACE Corpus Christi Section
Oilfield Water Analysis:
What Does It all Mean?
CORPUS CHRISTI, TX – NACE SECTION MEETING
MAY 20, 2014
API RP 45 committee started 1958
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
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.
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)
RESULTS AND WHAT THEY MEAN I
ppm, mg/L, me/L
weight/weight or volume/volume
weight per volume, used by API
with distilled water
(milliequivalent/L): expression of chemical
combining power of the electrolyte in a fluid;
used to check balance of cations/anions
Patterns: used to compare various waters
by constituents; see API form
RESULTS AND WHAT THEY MEAN II
The single most important measurement
Normal oilfield range = 6-8
by CO2, H2S, Fe, bicarbonate, alkalinity
in pH are logarithmic: pH 8 = 10 x pH 7
RESULTS AND WHAT THEY MEAN III
Sodium (Na): 40 % of the Sodium Chloride (Brine)
Used to force balance the sum of cations and anions
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.
RESULTS AND WHAT THEY MEAN IV
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
In sour (H2S) systems: Look for Manganese (Mn).
Calcium Carbonate (CaCO3):
depends on temperature, pressure and
concentration of ions. Acid soluble.
of scale formation increases with:
Partial Pressure of CO2 decreases
Total pressure decreases as TDS decreases
Calcium Sulfate (CaSO4)
acid soluble but may be “converted”
depends on temperature, pressure,
of scale formation increases with:
Increase in temperature
Increase in dissolved salts, up to 150F
Increase in pressure
pH has little effect on CaSO4
Barium Sulfate (BaSO4)
Least soluble of all scales.
Scale likely to occur whenever both Ba and
SO4 are present in a water.
slightly with temperature
Increases slightly with dissolved salts
Increases slightly with pressure
pH, no effect on solubility
RESULTS AND WHAT THEY MEAN V
Chloride (Cl): 60% of the Sodium Chloride
compound (NaCl, Brine). NaCl will be generally 80% of
Sulfate (SO4): Combines with Ba & Ca to form
Carbonate (CO3): “P” Alkalinity found in water with
pH above 8.3
Bicarbonate (HCO3): “M” Alkalinity in water with pH
between 4.5 & 8.3. Buffers corrosiveness of brine.
RESULTS AND WHAT THEY MEAN VI
Specific Gravity: The weight of a test sample
compared to the weight of distilled water (1.0). TDS
Resistivity: Resistance to electrical charge. The
higher the resistivity the lower the salinity. Measured
Hydrogen Sulfide (H2S): Acid gas contributes to
Carbon Dioxide (CO2): Acid gas contributes to
Oxygen (O2): Most corrosive of gasses in
Corrosion in oilfield water is caused by one of the
Oxygen (O2):, does not affect pH; deep pits caused by
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
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
How will water analysis affect bacteria analysis? (Cl,
TDS, O2, H2S)