I. IGNATIADIS S. BETELU

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Herbert O’Neal’
5 years ago
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1 WATER ADDITIVES FOR PREVENTION OF CHEMICAL AND BACTERIAL CORROSION IN GEOTHERMAL SYSTEMS: COMPARATIVE STUDY OF THE EFFECTIVENESS OF NEW ORGANIC SURFACTANTS IN INHIBITING CARBON STEEL CORROSION IN ACTUAL GEOTHERMAL WATER I. IGNATIADIS S. BETELU

OBJECTIVE: The objective of this performance is: (i) (ii) to present, starting by the historical context of French geothermal energy, the indepth understanding of the mechanisms controlling the

2 OBJECTIVE: The objective of this performance is: (i) (ii) to present, starting by the historical context of French geothermal energy, the indepth understanding of the mechanisms controlling the carbon steel corrosion and the effectiveness of actual corrosion inhibitors, to compare their action to those of other molecules or formulations, which have not been marketed yet and to propose new bio-resourced ones. CONTEXT: Historical context of the French geothermal energy Exploitation of the Dogger aquifer of the Paris Basin: Dogger (Middle Jurassic), is lasted from about 174 to 163 M years ago. Paris Basin is the largest basin exploiting low enthalpy geothermal waters in Western Europe; Currently, 45 geothermal installations are exploiting the Dogger Aquifer with temperatures below 85 C and the energy is used primarily for the heating of housing networks and the production of hot water

CONTEXT: Historical context of the French geothermal energy Exploitation of the Dogger aquifer of the Paris Basin: The geothermal doublets are made up of wells (production and

The water flows assisted through the carbon steel casings to the surface and, after flowing through heat-exchangers, is re-injected into the same aquifer a few hundred meters farther

activity. The water is highly mineralized and contains dissolved gases, including H 2 S and CO 2.

4, total dissolved solids (TDS) between 6 and 35 g/l much of which is Cl-, [H 2 S, HS-] from 5 to 100 mg/l, [SO 4 2- ] from 300 to 1200 mg/l, [CO 2 /HCO 3 -] from 250 to 600 mg/l and

3 CONTEXT: Historical context of the French geothermal energy Exploitation of the Dogger aquifer of the Paris Basin: The geothermal doublets are made up of wells (production and injection, both about 1,800 m deep), and of surface installations. The operating principle is simple. The water flows assisted through the carbon steel casings to the surface and, after flowing through heat-exchangers, is re-injected into the same aquifer a few hundred meters farther away. Initially, field experience has shown that, in both production and injection well casings, made of carbon steel (an API K55 type), there is corrosion, scaling and bacterial activity. The water is highly mineralized and contains dissolved gases, including H 2 S and CO 2. The main characteristics of the waters are: temperatures ranging from 47 to 85 C, ph between 6.1 and 6.4, total dissolved solids (TDS) between 6 and 35 g/l much of which is Cl-, [H 2 S, HS-] from 5 to 100 mg/l, [SO 4 2- ] from 300 to 1200 mg/l, [CO 2 /HCO 3 -] from 250 to 600 mg/l and no O 2 under normal conditions. The concentrations of TDS, H 2 S/HS - and CO 2 /HCO 3 - vary from place to place and, in some cases i.e., for sulfides, at the same place with time and exploitation flowrate. Schematic of a geothermal doublet Carbon steel tubing from a corroded geothermal well SEM BRGM Iron sulfide scale from a corroded geothermal well TEM Desulfatomaculum geothermicum in a lemon shape with spores and vacuoles of gas

CONTEXT: Historical context of the French geothermal energy Exploitation of the Dogger aquifer of the Paris Basin: The geochemistry of water make it one of the most corrosive natural waters for

4 CONTEXT: Historical context of the French geothermal energy Exploitation of the Dogger aquifer of the Paris Basin: The geochemistry of water make it one of the most corrosive natural waters for carbon steel. The corrosion rate is of 0.4 mm/y. The scale formed under these conditions is composed mainly of iron sulfides (amorphous iron sulfide, then mackinawite, pyrrhotite, pyrite,..) and is not protective and sometimes causes pitting corrosion. The main bacterial strains are sulfate- and thio-sulfate-reducing and both produce hydrogen sulfide, H 2 S/HS-. Corrosion: Oxydation of Fe to Fe 2+ Reduction of H + to H 2 Fe + 2H + Fe 2+ + H 2 Scale: Precipitation of Fe x S y i.e. HS- + Fe 2+ FeS + H + Bacterial activity (SRB and TRB): SO 4 2- H 2 S/HS -

5 CONTEXT: Historical context of the French geothermal energy Exploitation of the Dogger aquifer of the Paris Basin: In order to improve operating conditions in exploitations, the whole of the doublets have been progressively treated, since 1989, with oil-sourced corrosion inhibitors that are marketed by some companies, among them SEPPIC, AQUAPROX, BWT, CECA, GE (W&PT), KURITA, NALCO (ECOLAB),. The organic corrosion inhibitors on the market are made up of various molecules. Their exact formulations are commercial secrets. Main molecules in formulations are: Alkyl-amines (NORAM O/OD from CECA) Alkyl-diamines (DINORAM O from CECA) Fatty amines like polyethoxylate-based formulations Polyoxyethylene cocoamines or Alkylamine-N,N-bis(2-omega-hydroxypoly (oxyethylene)ethyl), or Cocoalkylethoxylatedamines Quaternary ammonium salts, like C-alkyl 8-18-benzyldimethyle Chloride, or Benzalkonium Chloride Thor Acticide BAC 50 M Main solvent used is: diethylene glycol mono-ethylether or 2-(2-ethoxyethoxy) ethanol. No bio-sourced molecule was used alone or in formulation until now

OBJECTIVES: Historical context of the French geothermal energy Methodology used for testing the inhibitor efficiency: By combining and comparing

natural or reconstituted geothermal water, treated or no with some quantity of each inhibitor.

inhibitive action of the formulas tested as a function of immersion time and tensioactive compound concentration.

6 OBJECTIVES: Historical context of the French geothermal energy Methodology used for testing the inhibitor efficiency: By combining and comparing results gathered using various techniques, we were able to determine the mechanisms governing the action of the inhibitors and determine their effectiveness. Both gravimetric (weight loss) and electrochemical methods were used, with carbon steel XC38 coupons and/or electrodes immersed from the start in a natural or reconstituted geothermal water, treated or no with some quantity of each inhibitor. Stationary and rotating working electrodes and stationary and transitory electrochemical methods were used to measure corrosion rate and assess the inhibitive action of the formulas tested as a function of immersion time and tensioactive compound concentration. The scale produced on the metallic samples under different conditions was characterized using classical chemical and surface analysis methods such as optical microscopy, X-ray diffractometry, scanning electron microscopy (SEM). The effectiveness of the inhibitors in reducing the corrosion rate and in inhibiting the formation of iron sulfide scale is assessed and compared.

7 RESULTS: Exploitation of the Dogger aquifer of the Paris Basin: During the last 4 years, BRGM tested more than 20 individual molecules and qualified more than 10 new corrosion inhibitors, some of which are now the most commonly used for the treatment of wells. All of these products, injected in an actual geothermal environment, are known to be anticorrosive and anti-scale at the recommended doses (between 2.5 to 10 mg/l) and bactericide at large doses. Although some of the problems encountered when using these products have been resolved, their use is far from being risk-free. Other difficulties must be overcome, such as (i) under-deposit corrosion which, in most cases, takes the form of pitting and (ii) persistence of the non (bio)degradable molecules that compose inhibitors. Today, more than 20 individual novel bio-sourced molecules are tested under the same procedures and compared to oil-sourced commercial ones. Inhibition efficiency by electrochemical techniques = I corr (without inh) : current density in µa/cm 2 without inhibitor i corr( with inhib) : current density in µa/cm 2 in the presence of inhibitor icorr without inhib icorr (with inhib) icorr (without inhib) x 100

RESULTS: COMPARISON IN LAB BETWEEN MARKETED OIL SOURCED INHIBITORS AND NEW BIO-SOURCED PRODUCTS Polarization resistance (Rp) technique for courant density (µa/cm²) determination: Inhibitor content

8 RESULTS: COMPARISON IN LAB BETWEEN MARKETED OIL SOURCED INHIBITORS AND NEW BIO-SOURCED PRODUCTS Polarization resistance (Rp) technique for courant density (µa/cm²) determination: Inhibitor content (mg.l -1 ) Rp (ohm) E(Rp) (mv/ecs) I corr (Rp) (µa) Polarization with ±20mV at 0.1mV/s around E corr for I corr (Rp) without Inhibitor OS CI Marketed INCB INCB Efficiency of OS CI marketed at 10 ppm= 88.6%; of INCB1 at 160 ppm=79.4; of INCB7 at 160 ppm=63.04%

9 RESULTS: COMPARISON IN LAB BETWEEN MARKETED OIL SOURCED INHIBITORS AND NEW BIO-SOURCED PRODUCTS Tafel plots technique (Ta) technique for courant density (µa/cm²) determination: Inhibitor content (mg.l -1 ) E corr (mv/ecs) I corr (Ta) (µa) Without Inhibitor OS CI Marketed INCB Polarization with ±250mV around Ecorr at 0.166mV/s for I corr (CT) INCB Efficiency of OS CI marketed at 10 ppm= %; of INCB1 at 160 ppm=82.0; of INCB7 at 160 ppm=43.7%

10 RESULTS: COMPARISON IN LAB BETWEEN MARKETED OIL SOURCED INHIBITORS AND NEW BIO-SOURCED PRODUCTS Resistance (R w ) from Electrochemical impedance Spectroscopy technique for courant density (µa/cm²) determination: Sweeping of frequencies carried out in E corr between 10 5 and 10-3 Hz. Interval of disturbances of ±10 mv around Ecorr for I corr (Z) Without Inhibiteur Inhibitor content (mg.l -1 ) R w (ohm) I corr (Z) (µa) calculated via R w OS CI Marketed INCB INCB Efficiency of OS CI marketed at 10 ppm= 91.6%; of INCB1 at 160 ppm=76.25; of INCB7 at 160 ppm=65.9%

Bio sourced inhibitors (anionic and cationic type) Novel bio-sourced inhibitors are fairly effective (or ineffective), even if are tested at higher dose (more than 10 times higher) that the classical

11 CONCLUSIONS AND PERSPECTIVES Oil sourced inhibitors (mainly of cationic type) All of the inhibitors tested at dose between 2.5 to 10 mg/l, significantly reduce the carbon steel corrosion rate with efficiency > 75% and often > 90% and delay the crystallization of mackinawite from amorphous iron sulfide scale. Bio sourced inhibitors (anionic and cationic type) Novel bio-sourced inhibitors are fairly effective (or ineffective), even if are tested at higher dose (more than 10 times higher) that the classical organic inhibitors. They are biodegradable (without presence of ethoxylate, nor amines), have a LHB equivalent to that of classical Synthesis, screening and testing for efficiency of bio-sourced inhibitors will continue. because it s worth seeing For the moment, all the products are under Intellectual Property Protection for Trade Secrets. THANK YOU FOR YOUR ATTENTION

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