Abstract

Hydrates can agglomerate and block pipelines causing blowouts and serious harm to personnel in addition to stopping production. They may contain as much as 30% H2S. Thermodynamic inhibitor (THI) methanol is the default method for addressing hydrate problems. Methanol can dissolve corrosion inhibitors (CIs), leading to increased corrosion rates. Alternatives are kinetic hydrate inhibitors (KHIs) but their performances are negatively affected by CIs, and they may not be suitable for sour conditions. The objective of this work was to develop anti-agglomerates (AAs) alternatives to THI and KHI that simultaneously provide corrosion protection while functioning in a sour environment.

Gas hydrate analysis was done in a gas hydrate autoclave up to 1915 psi (13,203 KPa) using 1-8% H2S, 3% CO2 and remaining CH4 at 4 °C. AAs were tested with and without alkylpyridine CI (CI-1) and torque values were used to measure performance. Selected AAs were tested to ascertain their effect on corrosion in low, medium and high salinity brine. Also corrosion studies were conducted in a benchtop autoclave at different operating parameters; temperature (22, 30, 50, 80 and 120 °C), H2S composition (4%, 20% and 35%), CO2 (3%, 4% and 10%) at total pressure of 350 psi (2413.2 kPa) and 1000 psi (6894.8 KPa). Testing was performed on 1018 carbon steel using a modified ASTM G170 method.

In hydrates testing, ≤ 2% quaternary compounds AC-1 and AC-2 (with CI-1) gave lower torque values (< 2.8 Ncm) compared to the blank (12.0 Ncm) and control (CI-1 only) (9.2 Ncm). Corrosion rate in 4% H2S, 3% CO2 at 22 °C was 24 and 12.41 mpy for the blank, while AAs (with CI-1) caused decrease in corrosion rate to 0.75 and 0.9 mpy for low and medium salinity brine respectively in the water phase.

For severe conditions at 120 °C, 20% H2S and 10% CO2, the blank gave a corrosion rate of 37.83 mpy with pitting whereas 200 ppm of V-53 (33% AC-1) and V-9 (33% AC-2) provided corrosion rates of 2.26 mpy and 2.62 mpy without pitting in the brine phase. In 35% H2S and 4% CO2, the blank showed a corrosion rate of 45.78 mpy with pitting whereas 200 ppm of CI-1 and specially formulated quaternary compounds (CI-2 and CI-3) provided corrosion rates of 2.57, 2.19 and 8.87 mpy without pitting in the synthetic brine phase.

The compounds presented in this paper were able to control hydrate agglomeration up to 100 % water cut, remained active in the presence of corrosion inhibitor and demonstrated corrosion protection in sour conditions.

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