Overview
ISO 20676:2018 specifies a method to determine hydrogen sulfide (H2S) content in upstream-area natural gas using laser absorption spectroscopy. The standard covers instrument selection, calibration, sampling, measurement procedure and uncertainty evaluation. The analytical range is 10 × 10−6 to 20 % (mole fraction) and can be expanded with specific instrument requirements. ISO 20676:2018 is intended for working-field natural gas analysis in upstream operations.
Key topics and technical requirements
- Measurement principle: Semiconductor laser beam transmitted through the sample; absorbance follows the Lambert–Beer law.
- Analytical range: 10 × 10−6 to 20 % (mole fraction); expandable with instrument-specific capabilities.
- Instrument requirements:
- Signal/noise ratio greater than 2:1 across analytical range.
- Light transmission > 10 % before sample introduction.
- Laser generator warm-up: follow manufacturer instructions; if unspecified, 48 h before first use and 1 h after power-on.
- Gas pressure at analyser inlet: 0.2 MPa to 0.4 MPa (use regulator with minimal internal volume, stainless steel or deactivated materials).
- Calibration:
- Use certified H2S calibration gas with methane as balance gas.
- Methane purity > 999 mmol/mol, H2S impurity ≤ 0.1 μmol/mol.
- Calibration frequency: user-defined but at least annually.
- Accepted calibration methods (per ISO 11095): bracketing, response formula simulation (≥3 calibration gases), one-point (with ≤20 % relative difference requirement).
- Sampling:
- Follow ISO 10715 sampling guidelines.
- Use materials inert to sulfur compounds; condition samples to remove liquid water, dust and liquid hydrocarbons.
- Reagents and absorbers:
- 10 % (mass fraction) NaOH solution recommended for H2S absorption (other absorbing compounds allowed).
- Quality and reporting:
- Includes sections on repeatability and uncertainty evaluation to support data quality.
- Safety: H2S is poisonous; implement appropriate health and safety measures.
Applications and users
ISO 20676:2018 is practical for:
- Upstream oil & gas operators conducting wellhead and field gas testing
- On-site and portable analyser manufacturers designing laser H2S analysers
- Field technicians and lab analysts responsible for process control, safety monitoring, and regulatory compliance
- Pipeline and custody-transfer personnel requiring reliable H2S quantification
Typical uses: continuous monitoring, spot-checks, process optimization, H2S mitigation, environmental and personnel safety controls.
Related standards
- ISO 10715 - Natural gas - Sampling guidelines (normative reference)
- ISO 11095 - Linear calibration using reference materials (normative reference)
- Other sulfur analysis standards referenced in ISO introduction:
Keywords: ISO 20676:2018, hydrogen sulfide, H2S, natural gas, upstream area, laser absorption spectroscopy, calibration, sampling, ISO 10715, ISO 11095.