What is a Sour Environment?
NACE defines a Sour environment as one that contains enough H2S either in the gaseous or aqueous media.
Properties of Hydrogen Sulphide
- Chemical Formula: H2S
- Odour: Rotten Egg
- Boiling point: 60OC
- Specific Gravity: 1.19
- Odour level: 0.13 mg/kg
Fatality of Hydrogen Sulphide (mg/kg)
- Respiratory breakdown: 100
- Nerve paralysis: 150
- Nausea, Dizziness: 200
- Unconsciousness: 500
- Asphyxiant, Fatal: 700
What is Sour Service?
Sour Service is defined as a fluid service containing water as liquid & H2S exceeding the limits defined below:
Sour Gas Service is defined as the gas service
IF Total Pressure of the gas being handled is > = 65 PSIA
AND Partial Pressure of H2S in the gas is > 0.05 PSIA
Then The Environment is SOUR Gas
Sour Oil and Multi-phase
IF Fluid handled is Crude or Crude+Water+Gas
- Gas to Oil Ratio > 5000 (SCF/bbl)
- H2S content in Gas-phase > 15%
- Partial Pressure of H2S in Gas Phase > 10 PSIA
- Surface operating Pressure > 265 PSIA
Then The Environment is SOUR Oil
Sour Scenario in the oil industry as per NACE MR-01-75
Refer to the below image (Fig. 1) which shows a curve segregating the sour and non-sour region as per NACE MR-01-75. The curve denotes the amount of H2S requirement for qualification of being Sour at a given absolute pressure.
Limitations of NACE MR-01-75
- Saltwater wells, injection wells
- Downstream Industries, Petrochemical
- Refineries and Chemical plants
- Low-pressure multiphase systems
HIC Scenario – API Nelson Curves
Refer to Fig. 2 which shows the HIC and Non-HIC regions.
Sour Scenario as per ISO 15156 / EFC 16
Fig. 3 shows the sour service criteria as per ISO 15156/EFC 16.
Sour Service H2S ppm Criteria as per DEP
Shell DEP provides the following H2S criteria for fluid services
- 0 to 49 PPM: Sweet Service
- 0 to 499 PPM: Low-Risk Sour Service
- 500 + PPM: High-Risk Sour Service
Hydrogen Sulphide – What it Can Do!
- Hydrogen- Hydrogen Induced Cracking (HIC)
- Sulphide- Sulphide Stress Cracking (SSC)
Dynamics of Sour Environments
Fig. 4 shows the dynamics of the sour service environment.