Publications FATC 2026 · #129

Conference poster · FATC 2026 · #129

Comparative Analysis of Carbonatic Scaling on DLC-Coated and Bare Hastelloy

Fabio de Assis Ressel Pereira1*, Romulo Fieni Fejoli2, Edson José Soares3, Nathan Fantecelle Strey2, Rubson Mação Camporez2, Leonardo Venâncio Curitiba3, Elisio Caetano Filho4, Marcelo Torres Piza Paes4, Felipe Mauro Rena Cardoso4, Andre Leibsohn Martins4, Giselle Maria Lopes Leite da Silva4

1 Industrial Technology Department, UFES · 2 Graduate Program in Mechanical Engineering, UFES · 3 Graduate Program in Energy, UFES · 4 Petrobras, Rio de Janeiro, Brazil · * fabio.a.pereira@ufes.br

Presented at the SPE Brazil Flow Assurance Technology Congress — FATC 2026 · Rio de Janeiro, November 4–6, 2026

Page link: www.brazflow.com/posters/fatc-129/

−63%CaCO3 mass on internal coupons, DLC vs. bare Hastelloy
−45%CaCO3 mass on external coupons, DLC vs. bare Hastelloy
100 bar · 90 °CCO2 pressure and temperature in the HPHT reactor
Aragonitedominant polymorph (needles), followed by calcite and vaterite

Analysis

About this work

Objective

To find out whether a diamond-like carbon (DLC) coating reduces CaCO3 scaling on Hastelloy C-276 — a corrosion-resistant alloy used in HPHT wells — as a passive alternative to chemical treatment. DLC films are hard, low-friction and stable up to 260 °C.

Approach

Bare and DLC-coated coupons were mounted side by side in the same rotating cage and tested together in our HPHT reactor (100 bar CO2, 90 °C, 125 rpm), so both surfaces saw exactly the same brine, flow and depressurization. Scale was quantified by gravimetry and examined by optical microscopy.

What we found

  • DLC reduced the CaCO3 mass by 63% on internal coupons (38.6 → 14.4 mg) and by 45% on external coupons (51.4 → 28.4 mg).
  • Bare Hastelloy was covered by a uniform layer; on DLC the deposit was sparse and discontinuous.
  • Aragonite needles dominated, followed by calcite and flower-like vaterite. DLC hinders the calcite base layer that anchors aragonite, which results in a less adherent scale.
  • External coupons scaled more than internal ones on both surfaces: flow conditions matter as much as the surface itself.

Why it matters

A coating that roughly halves the scale and weakens how it anchors to the wall is a promising passive mitigation for HPHT wells — especially where continuous chemical treatment is limited.

Experimental setup

Experimental conditions and tests performed

Tests performed

SurfacePositionCaCO3 mass (mg)DLC vs. bare
Bare HastelloyInternal38.6—
Hastelloy + DLCInternal14.4−63%
Bare HastelloyExternal51.4—
Hastelloy + DLCExternal28.4−45%

One test with both surfaces in the same cage; CaCO3 mass from Figure 3.

Test conditions

Reactor
HPHT rotating-cage reactor
Coupons
Hastelloy C-276, bare and DLC-coated, internal and external positions — mounted alternately in the same cage
Gas
100 bar of CO2
Temperature
90 °C
Rotation
125 rpm
Brine
High-salinity NaCl brine with Ca2+ and HCO3− (tables)
Volumes
Solution A 2,750 mL · Solution B 250 mL
Trigger
Depressurization → CO2 flashing → CaCO3 deposition

Solution composition

ReagentSol.Sol. (mg/L)Mixture (mg/L)
NaHCO3A1,5141,387
NaClA140,906129,164
CaCl2·2H2OB296,15624,680

Final mixture — ions

IonMixture (mg/L)
Na+51,190
HCO3−1,008
Cl−90,258
Ca2+6,728

Analyses

  • Gravimetry — CaCO3 mass on bare and DLC-coated coupons
  • Optical microscopy — coupon surfaces, reactor viewing window and solution collected from the reactor
  • Polymorph identification by crystal habit — aragonite, calcite and vaterite

From the poster

Poster figures

Select a figure to open it at full size.

Rotating cage before (a) and after (b) the test.
Figure 1. Rotating cage before (a) and after (b) the test.
Coupons before and after the test (DLC-coated coupons are the bluish ones).
Figure 2. Coupons before and after the test (DLC-coated coupons are the bluish ones).
CaCO3 mass on bare and DLC-coated Hastelloy.
Figure 3. CaCO3 mass on bare and DLC-coated Hastelloy.
CaCO3 polymorphs: (a) reactor viewing window; (b) solution collected from the reactor (50 µm).
Figure 4. CaCO3 polymorphs: (a) reactor viewing window; (b) solution collected from the reactor (50 µm).
Coupon surfaces after the test: bare Hastelloy and Hastelloy + DLC (50 µm).
Figure 5. Coupon surfaces after the test: bare Hastelloy and Hastelloy + DLC (50 µm).

From the lab

More images from the tests

Images from the same test (test 27, August 2025: 90 °C, 100 bar CO2, 125 rpm) that are not shown in the poster — including 3D surface profilometry of the coupons.

3D surface profilometry of coupons after the test, bare Hastelloy (top) and Hastelloy + DLC (bottom), same horizontal scale. Colour indicates surface height.
3D surface profilometry of coupons after the test, bare Hastelloy (top) and Hastelloy + DLC (bottom), same horizontal scale. Colour indicates surface height.
External DLC-coated coupon after the test, optical microscopy (50 µm scale bar).
External DLC-coated coupon after the test, optical microscopy (50 µm scale bar).
Crystals collected from the reactor after the test: aragonite needles and calcite rhombohedra (50 µm).
Crystals collected from the reactor after the test: aragonite needles and calcite rhombohedra (50 µm).
Rotating-cage disc after the test.
Rotating-cage disc after the test.

References

  1. Kamal, M. S. et al., 2018. Oilfield scale formation and chemical removal: a review. J. Pet. Sci. Eng., 171, pp. 127–139.
  2. Cosmo, R. P. et al., 2022. Modeling and validation of the CO2 degassing effect on CaCO3 precipitation using oilfield data. Fuel, 310(B), 122067. doi:10.1016/j.fuel.2021.122067
  3. Zancanella, A. C. B. et al., 2025. Evaluation of the surface finish on 304 stainless steel as a way to mitigate CaCO3 scaling. Surfaces, 8(1), 13.
  4. Tallant, D. R. et al., 1995. The thermal stability of diamond-like carbon. Diamond Relat. Mater., 4(3), pp. 191–199.
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