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Retention Improvement Of Sulfonic Acid Based Scale Inhibitor On Sandstone Formations At HTHP Conditions

Oilfield waters have a complex composition depending on reservoir rock at different geographical locations that can be carried into the production water1. The alteration in environmental conditions such as pressure, temperature, salt content or pH can cause the liquid to oversaturate and the contained ions to form complexes. These will precipitate out of the solution, deposit and grow on contacting surfaces such as reservoirs, upstream production tubing, sub-surface safety valves, water injection lines to top side refining equipment namely heat exchangers and transport lines 2–4. Scaling can also be induced by incompatible mixing of fluids. For example CaCO3 and /or BaSO4  form through typical mixing of SO4 2- containing sea water with the formation water that carries high concentrations of divalent cations such as Ca2+and Ba2+2. Similarly, sulfide scales form upon mixing with H2S-containing  formation water enriched with Fe, Zn or Pb ions 5. ZnS and PbS have been observed to form in presence of only 25 ppm H2S at gulf of Mexico containing 50 ppm Zn and 5 ppm Pb , due to their low solubility constant Ksp 6,7.  

Product Number: 51322-17875-SG
Author: Yasmin Hayatgheib, Salima Baraka-Lokmane, Thibaut Charpentier, Wassim Taleb, Paul Thornton, John-Richard Ordonez-Varela, Richard Barker, Wassim Taleb, Anne Neville
Publication Date: 2022
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Recent environmental legislation has pushed many fields especially the Netherlands and UK continentals to phase out phosphorous based scale inhibitors (SI). However, remaining chemistries have mostly shown low tolerance to high salinity formation water (HS) or poor retention properties on the sandstone reservoir, rendering them unsuitable candidates for squeeze treatment. On the other hand, the high temperatures and pressures (HTHP) gas condensate wells require thermostable and compatible SI with HS that could suppress the full range of forming scales including: barium sulfate, calcium carbonate (BaSO4/ CaCO3), mixed zinc, lead and iron sulfide (ZnS/PbS/FeS). 

This work presents a thermally stable sulfonic acid base structure (phosphorous free) SI that provides adequate affinity to sandstone rock for squeeze treatment purposes up to 385°C. The designed inhibitor has high performance in HTHP conditions and is completely compatible with HS (200 g/L salinity), as well as high levels of calcium (20 g/L) and barium (3 g/L). At minimum concentration of 5 mg/L, scanning electron microscopy and energy dispersive x-ray results reveal disrupted sulfide scales and BaSO4 crystal growth and no traces of CaCO3 crystals. The adsorption isotherm analysis on sandstone, indicates pure adsorption for [SI] <100 mg/L and combined precipitation/adsorption behaviour for 100 mg/L< [SI] <1000 mg/L.  

Recent environmental legislation has pushed many fields especially the Netherlands and UK continentals to phase out phosphorous based scale inhibitors (SI). However, remaining chemistries have mostly shown low tolerance to high salinity formation water (HS) or poor retention properties on the sandstone reservoir, rendering them unsuitable candidates for squeeze treatment. On the other hand, the high temperatures and pressures (HTHP) gas condensate wells require thermostable and compatible SI with HS that could suppress the full range of forming scales including: barium sulfate, calcium carbonate (BaSO4/ CaCO3), mixed zinc, lead and iron sulfide (ZnS/PbS/FeS). 

This work presents a thermally stable sulfonic acid base structure (phosphorous free) SI that provides adequate affinity to sandstone rock for squeeze treatment purposes up to 385°C. The designed inhibitor has high performance in HTHP conditions and is completely compatible with HS (200 g/L salinity), as well as high levels of calcium (20 g/L) and barium (3 g/L). At minimum concentration of 5 mg/L, scanning electron microscopy and energy dispersive x-ray results reveal disrupted sulfide scales and BaSO4 crystal growth and no traces of CaCO3 crystals. The adsorption isotherm analysis on sandstone, indicates pure adsorption for [SI] <100 mg/L and combined precipitation/adsorption behaviour for 100 mg/L< [SI] <1000 mg/L.  

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