Dear Miguel and Lukas,
The standard heating value for natural gas of 39 MJ/Nm3 refers to the Higher/Gross Heating Value. Although this is meant to be the default assumption for all datasets producing or using natural gas, you are right that there is a number of datasets in which the property “heating value, net” is set to 39 MJ/Nm3. I agree this is confusing and we are therefore doing our best to correct the issue and provide more explicit documentation on the matter.
Values for the density of natural gas originate from ecoinvent version 2, where a density of 0.84kg/Nm3 was defined for sweet gas and of 1 kg/Nm3 for sour gas (see Tab. 3.4, p. 6 in Faist Emmenegger et al. 2007, pdf report 06_V_Erdgas accessible in the report section of ecoinvent version 2). With the standardization of the gas quality to (sweet) gas of 39 MJ/Nm3 gross heating value, the density was standardized to 0.84 kg/m3. The density of 1kg/m3 in the dataset “natural gas production, DE” was hence mistakenly retained from before the introduction of standardized gas quality and stems from the sour nature of natural gas in Germany.
Reference: Faist Emmenegger M., Heck T. and Jungbluth N. (2007) Erdgas. In: Sachbilanzen von Energiesystemen: Grundlagen für den ökologischen Vergleich von Energiesystemen und den Einbezug von Energiesystemen in Ökobilanzen für die Schweiz (ed. Dones R.). Swiss Centre for Life Cycle Inventories, Dübendorf, CHKind regards,Florentine BrunnerData Analyst, ecoinvent