東山油田周辺における原油の地球化学と移動・集積

抄録

Crude oils from five oil and/or gas fields and five wells in the region of the Higashiyama oil field, Niigata Prefecture, Japan, are divided into three groups (A, B, C) based on their geochemical characteristics:

Group A : the Higashiyama and Nagaoka oils, which are Niitsu-type with relatively low maturity.

Group B : the Mitsuke and Ohmo oils, which are Niitsu-type with relatively high maturity, and oils from the Shimodori and Shin-nishinagaoka wells.

Group C : the Nishi-nagaoka oil, and oil from the Kurosaka well, which are Kubiki-type. Similar oils include those from the Teradomari Formation in the Katakai gas field, including the Asahihara well.

Oils of groups A and B were probably generated in a depression between the Higashiyama and Mitsuke fields, as inferred from the geographic distribution and cumulative production of oil fields, the distribution of oil reservoirs in the Higashiyama field, and other factors. The oil maturity indicates that the Higashiyama oil migrated before the Mitsuke and Ohmo oils.

The Nishi-nagaoka oil was probably generated within the same depression as oils from the Katakai field, whose place may be located east to the Katakai field, given the geologic structure in the field.

This paper shows that geochemical analysis of crude oils stored for a long time provides valuable information on the classification and maturity of oils and the source rock.