ISO 20676:2018

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:
  • ISO 6326-3, ISO 6326-5, ISO 16960, ISO 19739, ISO 20729

Keywords: ISO 20676:2018, hydrogen sulfide, H2S, natural gas, upstream area, laser absorption spectroscopy, calibration, sampling, ISO 10715, ISO 11095.