南長岡における天然ガス生産, 輸送のライフサイクルインベントリ (LCI) 調査

抄録

The authors investigated life cycle carbon dioxide and methane inventories for the exploration, exploitation and transportation (incl. their capital) of natural gas produced in Minami Nagaoka Natural Gas Field in Japan. Around 22% of total domestic natural gas production was exploited from the field in 2001.
According to the results obtained through the investigation, 5.18g-CO₂-eq. of carbon dioxide and methane is released by the exploration, exploitation and transportation of 1 MJ of the natural gas. The amount is almost 10% of the carbon dioxide emission by the combustion of the natural gas. Hence, the emission data by its production should be counted for precise implementation of LCA.
The largest carbon dioxide emission source is the release of carbon dioxide which is extracted from underground with natural gas and separated from the target gas (CH₄). The next largest emission is released natural gas during its transportation by pipe lines. Because of re-construction of roads or development of the route area, the pipe lines are required to detour. For the diversion process, certain amount of natural gas inside the pipes is released to the environment. These releases are more than 70% of the total GHG emission obtained by this investigation.