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Conversion from Gas L to Gas H

In France, there are actually two types of natural gas distributed: gas L and gas H.

  • Gas L is imported from the Netherlands. It is distributed to the north of France.

  • As for gas H, it comes primarily from the northern sea, Russia, and Algeria. It is then distributed to the whole territory.


Mainly composed of methane (CH4) those two gases have however different characteristics.

Natural gas L characteristics

Gases L and H are defined by distinct calorific powers. Thus the power of gas L is lower than gas H’s (around 10kWh per m2 for gas L, and around 11,5 for gas H), because of a higher content in nitrogen for gas L. Moreover, those gases distinguish from one another by different distribution pressure, which is superior for gas L to compensate its lower calorific power (25 mbar vs 20 mbar for gas H).

The gas L market in Europe and the ending of the Groningue gas

In Europe, gas B comes mainly from the Groningue deposit in the Netherlands. It provides gas for about 15 million homes in a field englobing 4 European countries: Netherlands, Germany, Belgium and France.



Map of the deposit zone for gas L in Europe

At the beginning, known as one of the biggest natural gas deposit in western Europe, the Groningue deposit is actually coming out of stock. Before reaching the very end, the production has already been drastically decreased since several years because of the sismic waves created by the exploitation. In this context, contracts for the exportation of gas L won’t be renewed beyond 2029.


In France, the gas L network supplies in natural gas around 1,3 millions of client, among them hundreds of industrials directly linked to the transport network divided into 6 departments: the Nord, Aisne, Pas de calais, Somme, Oise and for a very limited number, the Seine-Maritime. Gas L represents around 10% of the whole French consumption. Therefore, for consumers using gas L, to let them be supplied in natural gas, it is mandatory that French operators achieve a conversion from gas L to gas H by 2029.



Map of the french territory concerned by the conversion

Let the conversion in gas H from the zone supplied in gas L

Currently, infrastructures in gas L are composed of: an entry point for the gas L exported to Taisnières-sur-Hon, an adapter at Loon-Plage which converts gas H in gas L on the transport network, an underground storage site at Gournay-sur-Aronde operated by Storengy, and transportation and distribution networks.


The conversion in gas H of the zone supplied in gas L will need to modify theactual infrastructure as well as to intervene into each client’s home. The switch will be progressively done, following a geographic division into around 20 sectors, at a rate compatible with the necessary operations for each client and according to a scheduling feasible for the flow on the network.

Transport network from gas L to gas H in the zone concerned by the conversion plan


A specific legislative and regulatory framework

The establishing of a specific legal framework was necessary to prepare this conversion, to define the operation schedule, the responsibilities of the different actors and the technical modalities acknowledged.

This framework was initiated by the article 164 of the law n° 2015-992 of August the 17th 2015 related to the energetic transition for the green growth, then completed by the decree n° 2016-348 of March the 23th 2016. It projects the establishment of a piloting phase on the period from 2016 to 2020, the jointed elaboration of a conversion plan project by the network and storage managers, and the establishment of a coordination committee. The urban communities concerned by the piloting phase have been determined by the law of July the 10th 2017.

GRDF, Gazélec Péronne, SICAE Somme et Cambraisis, Storengy and GRTgaz have collaborated very closely under the public authorities to create a conversion plan project, which was submitted to the ministres concerned on September the 23th 2016. This plan will then be established as a law, after a technical and economical evaluation by the CRE.

A progressive conversion plan between 2016 and 2029

The conversion into gas H from the actual gas L consumption zone relies on the division of the transport and distribution networks of gas L into around 20 geographical sectors (as seen on the image). The change in the gas type will be done independently and successively for each sector, letting a progressive conversion of the whole zone by 2029, at a rate compatible with the interventions necessary for each of the 1,3 million clients concerned.

Sectorization of the transport and distribution networks for the establishment of the conversion plan


Focus on the pilot phase (2018-2020)

The pilot phase is within the 2016-2020 period and concerns 47 urban communities determined by the law of July 2017. During this phase, the great principles of the conversion will be implemented on a panel of around 85,000 clients, residential as well as industrial and service sectors, divided into the sectors of Doullens, Gravelines, Grande Synthe and Dunkerque. In 2020, with the conclusions of the experimental pilot phase, the operational modalities will be adapted, before the launch of the deployment phase, in 2021.

Map of the pilot zone

The conversion project from gas L to gas H is a great span operation involving numerous actors on the national territory. The project is necessary to ensure continuity of supply for the gas L consumers. But it will also go beyond by reinforcing the gas procurement security of this part of the network. At last, this operation is also an opportunity to improve the energetic efficiency on a large geographical area, thanks to the interventions which will be achieved into each client’s home.



Sources : Gaz d’aujourd’hui, GRDF, GRTgaz

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