タイ沖ガス田における炭酸ガス起源の地質学的予察

抄録

In this paper, the distribution of carbon dioxide in natural gases recovered from the Platong gas field and its origin are discussed on the basis of geological evidences.
Carbon dioxide content in gases of this field is average 15% and partly more than 40%.
Gas bearing Tertiary sediments are dominated by gas-prone woody-coaly organic matters. Main east-dipping faults in the western flank of this structure cut basement complex. Gas reservoirs containing rich carbon dioxide, more than 40%, are locally distributed in the northwestern part of this field. The spatial spread is clearly oblique to stratigraphic markers and is like “conical mass”. This mass is characterized by high density shale more than 2.70gm/cc and very low Cl^- content in formation water.
The above marked features suggest that carbon dioxide has been generated from woody-coaly kerogen in sediments during thermal diagenesis, and also has been supplied from “magmatic origin” through the faults, and/or formed by oxidation of hydrocarbons through contact with mineralized waters, which have ascended into Tertiary sediments along fractures and fault zones.