ISO 23978:2020

INTERNATIONAL ISO
STANDARD 23978
First edition
2020-09
Natural gas — Upstream area —
Determination of composition by
Laser Raman spectroscopy
Reference number
©
ISO 2020
© ISO 2020
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ii © ISO 2020 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 2
4.1 Working principle of the laser Raman analyser . 2
4.2 Calculation . 3
5 Instruments . 3
5.1 Laser Raman gas analyser . 3
5.2 Laser specifications . . 4
5.3 Detection module . 4
5.4 Signal processing and user interface . 4
5.5 Sample filtration and probe . 4
5.6 Gas pressure regulator . 4
5.7 Sulfur compound absorber. 5
6 Reagents and materials . 5
6.1 Zero gas . 5
6.2 Base span calibration gases . 5
6.3 Working span calibration gases. 5
7 Measurement procedures . 5
7.1 preparation . 5
7.2 Calibration . 6
7.2.1 Calibration frequency . 6
7.2.2 Calibration procedure . 6
7.2.3 Zero calibration . 6
7.2.4 Base span calibration . 6
7.2.5 Working span calibration . 6
7.3 Sampling and sample analysis . 6
7.4 Data record . 7
8 Repeatability . 7
9 Uncertainty evaluation . 7
9.1 General . 7
9.2 Uncertainty of I and I . 7
i Ri
9.3 Uncertainty of C . 8
Ri
9.4 Uncertainty of result . 8
10 Test report . 9
Annex A (informative) Statistical procedure for estimation of the repeatability .10
Bibliography .17
Foreword
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This document was prepared by Technical Committee ISO/TC 193, Natural gas, Subcommittee SC 3,
Upstream area.
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iv © ISO 2020 – All rights reserved

Introduction
Gas chromatography methods for determination of composition in natural gas already exist as
ISO 6974-1 to ISO 6974-6 or ISO/TR 14749.
Gas laser Raman spectrometry is a simpler and more direct analysis method than gas chromatography.
Gas laser Raman offers a faster and more convenient means of determining composition of upstream
area natural gas because it is an entirely optical method operating at the speed of light with no moving
parts. Natural gas exploration and development benefits from fast determination of gas composition
and real-time monitoring of gas composition better optimizes natural gas treatment processes.
Gas laser Raman spectrometry enables rapid and simultaneous analysis of multiple gas species
because each type of gas molecule emits unique light frequencies shifted from the frequency of laser
light striking it. This "Raman scattering" is instantaneous and directly proportional to the number of
molecules the light impacts. This simple principle allows continuous on-site real-time data monitoring
and control, it will bring tremendous improvements to gas exploration, well operations, transport, and
processing.
INTERNATIONAL STANDARD ISO 23978:2020(E)
Natural gas — Upstream area — Determination of
composition by Laser Raman spectroscopy
1 Scope
This document describes a laser Raman spectroscopy method for the quantitative determination of
chemical composition of natural gas in upstream area.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 6142-1, Gas analysis — Preparation of calibration gas mixtures — Part 1: Gravimetric method for Class
I mixtures
ISO 6144, Gas analysis — Preparation of calibration gas mixtures — Static volumetric method
ISO 6145, Gas analysis — Preparation of calibration gas mixtures using dynamic methods
ISO 10715, Natural gas — Sampling guidelines
ISO 11095, Linear calibration using reference materials
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
Raman effect
process, in which photons from a light source are absorbed by the electrons surrounding polyatomic
molecules and result in a new photons being emitted at wavelengths higher or lower than the source
photon wavelength
Note 1 to entry: The resulting wavelength changes are called Raman shifts. The Raman shifts are determined by
the vibrational and rotational frequencies of the atomic bonds within each molecule.
3.2
multichannel photodetector
photosensitive semiconductor device that transports electric charge from one capacitor to another,
allowing serial output of parallel data, typically used for digital image capture
3.3
avalanche photodiode
APD
diode with an internal gain mechanism
Note 1 to entry: As in the case of standard diodes, photons generate electron-hole pairs, which are accelerated
by the applied external voltage such that further electrons are introduced to the conduction band by means of
impact ionization. These secondary el
...