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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. API RP 45 committee started 1958 Published 1968 Latest version 1998 No current NACE Standard APPLIED WATER TECHNOLOGY

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NACE Corpus Christi, TX – Nace Section Meeting May 20, 2014

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

  2. 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 History

  3. 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. What’s Important

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

  5. 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 Results and What They Mean I

  6. pH • 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 Results and What They Mean II 0714

  7. 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. Results and What They Mean III

  8. 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). Results and What they Mean IV

  9. 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 Scale Formation

  10. 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 Scale Formation

  11. 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 Scale Formation

  12. Anions Chloride (Cl):60% of the Sodium Chloride compound (NaCl, Brine). NaCl will be generally 80% of TDS. Sulfate (SO4): Combineswith 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 & 8.3. Buffers corrosiveness of brine. Results and What They Mean V

  13. 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. Results and What they Mean VI

  14. 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. Corrosion

  15. 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) Conclusion

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