Abstract
The Aga-oki oil and gas field, offshore Niigata, Japan, consists of two parallel anticlinal structures, which are called the West and East structures.
The geochemical data of oils from the Shiiya Formation such as light hydrocarbons and biomarkers indicate that the oil from the West structure is more degraded and less mature than that from the East structure.
The difference in maturity of oils probably reflects a difference in the kitchen area: the geochemical data of oil and condensate from two exploratory wells suggest that the oil from the West structure has migrated from the southwest kitchen area, while the oil from the East structure has migrated from the east kitchen area.
