Corrosion-Driven Material Selection for ESPs in a Highly Sour HPHT Environment
CMSProdex was invited to perform material selection for an ESP installed in the well producing oil, gas, and water. Based on the CO₂/H₂S partial pressure ratio, the system falls within the sour corrosion regime. Corrosion rates were calculated using Water Chemistry Model – Modul Corrosion. Based on in situ pH and H₂S partial pressure, the system was classified as high-risk – severe sour service (Region 3 environment) in accordance with NACE MR0175/ISO 15156, with susceptibility to SSC and HIC.
Project background
The project was carried out in a mature offshore field in the Gulf of Mexico, producing from a depth of approximately 15000 ft. The relevant data are presented in the table below.
| Common Parameters | Value | API/SI Unit |
|---|---|---|
| Production | Offshore | — |
| H₂S | 0.651 | % mol |
| CO₂ | 3.489 | % mol |
| Chlorides | Could be >100000 | ppm |
| Elemental sulphur pH | Could be present 4.8–5.1 (calculated) | — |
| ESP System | Value | API Unit | Value | SI Unit |
|---|---|---|---|---|
| ESP Depth | 12336 | feet | 3760 | m |
| Pump Intake Pressure | 2826 | psi | 194.8 | bar |
| Pump Discharge Pressure | 4404.3 | psi | 303.7 | bar |
| Bottom Hole Flowing Pressure | 4120 | psi | 284.1 | bar |
| Pump Intake Temperature | 264.4 | °F | 129.1 | °C |
| Pump Discharge Temperature | 301 | °F | 149.4 | °C |
| Bottom Hole Temperature | 301.3 | °F | 149.6 | °C |
| ppH₂S @ Intake Pressure | 18.40 | psi | 1.27 | bar |
| ppH₂S @ Discharge Pressure | 28.67 | psi | 1.98 | bar |
| ppCO₂ @ Intake Pressure | 98.60 | psi | 6.80 | bar |
| ppCO₂ @ Discharge Pressure | 153.67 | psi | 10.59 | bar |
Challenge
The challenge of material selection for this case study was to define and specify suitable materials for ESP components, based on a comprehensive assessment of the classified environment, operating parameters, fluid properties, and the applied artificial lift method. The selected materials had to ensure long-term system integrity, reliability, and performance by effectively mitigating risks associated with corrosion degradation mechanisms. The main challenges can be summarized as: severe sour service, extremely high chlorides content, possible presence of elemental sulfur, mildly acidic environment, HPHT.
Solution
Partial pressures of H₂S and CO₂, pH at the depth of ESP installation, corrosion rates, possibility and impact of FeS and FeCO₃ protective films formation were evaluated using Water Chemistry Model – Modul Corrosion. This model enables estimation of corrosion rates of carbon steel in CO₂, H₂S and combined CO₂/H₂S environments, including the formation of FeCO₃ and FeS films and their impact on the final corrosion rate in the system is included. Materials for ESP components operating in sour environments were selected in accordance with NACE MR0175/ISO 15156 standard.
Results and Impact
- The CO₂/H₂S partial pressures and their ratio classify the studied environment as a high-risk according to NACE MR0175/ISO 15156, with susceptibility to SSC and HIC.
- HPHT conditions combined with severe sour service and extremely high chloride concentrations significantly narrow the range of suitable materials and require strict compliance with NACE MR0175/ISO 15156.
- The expected dominant corrosion degradation mechanisms are summarized as follows:
- Sulfide Stress Cracking (SSC)
- Chloride-induced Stress Corrosion Cracking (SCC)
- Pitting / Crevice Corrosion
- The results indicated dominant precipitation of FeS over FeCO₃ and the formation of stable FeS film. Dominant FeS film formation does not eliminate corrosion risk, as susceptibility to SSC, chloride-induced SCC, and localized corrosion mechanisms remains high.
- Carbon steel and conventional stainless steels are unsuitable for this environment without robust corrosion mitigation or cladding solutions.
Lessons Learned / Key Takeaways
Material selection for ESP components must consider not only corrosion resistance but also long-term integrity, reliability, and failure consequences in high-risk sour environments.
A systematic, model-based approach to material selection reduces uncertainty, minimizes operational risk, and supports sustainable ESP performance throughout the asset life.
Quick Facts
Location
Gulf of Mexico
H₂S:
0.651 mol % - severe sour service
CO₂:
3.489 mol % - moderate
Chlorides:
> 100,000 mg/L - extremely high (very aggressive brine)
Elemental sulfur:
likely, adds severe risk for localized corrosion and pitting
pH:
4.8 - mildly acidic, promotes corrosion