Publications FATC 2026 · #128

Conference poster · FATC 2026 · #128

Evaluation of Anti-Scaling Additive on CaCO3 Deposition Under Simulated Oil Well Conditions

Fabio de Assis Ressel Pereira1*, Leonardo Venancio Curitiba2, Domenico Andreatta2, Rafael de Paula Cosmo2, Romulo Fieni Fejoli2, Rodrigo Simões Maciel2

1 Industrial Technology Department, Federal University of Espírito Santo (UFES), Brazil · 2 BrazFlow Labs, UFES startup, 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-128/

≈20%less CaCO3 on the coupons with the antiscalant
≈30 bar → 1 atmprecipitation onset delayed until full depressurization
≈7 Nload needed to detach the deposit formed with crude oil
3 testsreference · antiscalant · antiscalant + oil

Analysis

About this work

Objective

To test whether a phosphonate antiscalant controls CaCO3 scaling when precipitation is driven by CO2 degassing — the mechanism behind carbonate scale in pre-salt wells — and how the presence of crude oil changes the result.

Approach

Three runs in our HPHT rotating-cage reactor with the same brine, temperature and depressurization: a reference, one with 20 mg/L of antiscalant, and one with antiscalant plus 300 mL of crude oil. Deposits were evaluated by mass (gravimetry), crystal morphology (optical microscopy) and adhesion (scratch test).

What we found

  • The antiscalant reduced the CaCO3 mass by about 20% on both internal (103.3 → 82.2 mg) and external coupons (59.2 → 47.5 mg), and the cage came out visibly cleaner.
  • It delayed precipitation: without additive, crystals appeared at ≈30 bar during depressurization; with the antiscalant, only after reaching 1 atm.
  • It changed the crystals: smaller, irregular particles instead of the large, well-formed crystals of the reference test.
  • With crude oil, internal coupons collected less CaCO3 (55.7 mg), while external coupons collected 73.6 mg; the deposit formed heterogeneous aggregates and adhered strongly — in the scratch test the film only detached at ≈7 N, whereas the indenter quickly reached the steel in tests 1 and 2.

Why it matters

Antiscalants are usually ranked by how much deposit they prevent. Under realistic HPHT conditions with oil, a smaller deposit mass came together with a deposit that is much harder to remove. Morphology and adhesion should therefore be part of antiscalant qualification — not only mass.

Experimental setup

Experimental conditions and tests performed

Tests performed

TestAntiscalant (20 mg/L)Crude oil (300 mL)CaCO3 internal (mg)CaCO3 external (mg)
1 — Reference——103.359.2
2 — Antiscalant✓—82.247.5
3 — Antiscalant + oil✓✓55.773.6

Average CaCO3 mass per coupon (8 coupons per position), from Figure 3.

Test conditions

Reactor
HPHT rotating-cage reactor
Coupons
16 × AISI 316L (internal and external positions)
Rotation
125 rpm (Re ≈ 37,685)
Temperature
80 °C
Gas
Solution A saturated with 50 bar of CO2
Ca2+ injection
Solution B injected with N2 (+40 bar)
Trigger
1 h depressurization → CO2 degassing → CaCO3 precipitation
Volumes
Solution A 2,750 mL · Solution B 250 mL
Antiscalant
Phosphonate, 20 mg/L
Crude oil
300 mL (test 3)

Solution composition

ReagentSol.Sol. (mg/L)Mixture (mg/L)
NaHCO3A6,8736,301
CaCl2·2H2OB66,1605,513

Final mixture — ions

IonMixture (mg/L)
Na+1,724
HCO3−4,576
Cl−2,659
Ca2+1,503

Analyses

  • Gravimetry — CaCO3 mass on internal and external coupons
  • Optical microscopy — reactor viewing window, solution collected from the reactor and coupon surfaces
  • Scratch test — progressive load from 0.5 to 10.5 N to assess deposit adhesion
  • Precipitation onset — observed through the reactor window during depressurization

From the poster

Poster figures

Select a figure to open it at full size.

Rotating-cage parts after tests 1, 2 and 3.
Figure 1. Rotating-cage parts after tests 1, 2 and 3.
CaCO3 on internal and external coupons.
Figure 2. CaCO3 on internal and external coupons.
Average CaCO3 mass on the 316L coupons (8 coupons per bar).
Figure 3. Average CaCO3 mass on the 316L coupons (8 coupons per bar).
Crystals at the reactor viewing window and in the solution collected from the reactor (25 µm).
Figure 4. Crystals at the reactor viewing window and in the solution collected from the reactor (25 µm).
Crystal morphology on internal and external coupons (25 µm).
Figure 5. Crystal morphology on internal and external coupons (25 µm).
Scratch tracks, load increasing from 0.5 to 10.5 N from right to left (1000 µm). ✸ marks film detachment.
Figure 6. Scratch tracks, load increasing from 0.5 to 10.5 N from right to left (1000 µm). ✸ marks film detachment.

From the lab

More images from the tests

Photographs from two complementary tests run in the same reactor in May 2026 — test 63 (without additive) and test 64 (with antiscalant additive) — at 90 °C, 50 bar CO2 + 50 bar CH4, 125 rpm, with AISI 316L coupons. They are not part of the poster results; they show the same comparison with a CO2/CH4 gas mixture.

Coupons after the test

Test 63 — without additive
Test 63 — without additive
Test 64 — with additive
Test 64 — with additive

Crystals collected from the reactor (50 µm scale bar)

Test 63 — without additive
Test 63 — without additive
Test 64 — with additive
Test 64 — with additive

Internal coupon surface (50 µm scale bar)

Test 63 — without additive
Test 63 — without additive
Test 64 — with additive
Test 64 — with additive

External coupon surface (50 µm scale bar)

Test 63 — without additive
Test 63 — without additive
Test 64 — with additive
Test 64 — with additive

Rotating-cage disc after the test

Test 63 — without additive
Test 63 — without additive
Test 64 — with additive
Test 64 — with additive
Test 63 — coupons before the test.
Test 63 — coupons before the test.
Test 63 — coupons after rinsing: the adhered layer remains.
Test 63 — coupons after rinsing: the adhered layer remains.
Test 63 — crystals seen through the reactor viewing window (25 µm).
Test 63 — crystals seen through the reactor viewing window (25 µm).
Test 64 — base of the rotating cage after the test.
Test 64 — base of the rotating cage after the test.
Test 64 — deposit collected after the test.
Test 64 — deposit collected after the test.

References

  1. Tang, Y. et al., 2008. Investigation of CaCO3 scale inhibition by PAA, ATMP and PAPEMP. Desalination, 228, pp. 55–60.
  2. Wang, Z., Neville, A., Meredith, A. W., 2005. How and why does scale stick? SPE International Symposium on Oilfield Scale.
  3. 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
  4. Maciel, R. S. et al., 2025. Unraveling the hydrodynamic effects on CaCO3 scaling under HTHP CO2 degassing. Petroleum Science, 23, pp. 434–446. doi:10.1016/j.petsci.2025.09.040
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