2013 Volume 78 Issue 3 Pages 265-275
Interpretation on radiolarian fossil data of Nakaseko and Sugano (1972) based on Kato and Obuse (2013) shows that oil reservoirs in the Amarume oil field, Yamagata Prefecture, belong to the lower part of the Kitamata Formation and the Kusanagi Formation. This result harmonizes with foraminiferal fossil assemblages in wells around the field.
Oils produced in the field, Amarume oils, are mostly classified into light oil and slightly biodegraded. Medium oils in the southern part of the field are strongly biodegraded due to meteoric waters invaded from the south.
The Amarume oils resemble oils in the Yurihara and Ayukawa fields in geochemical characteristics including relationship between API gravity and sulfur content, carbon isotope compositions of oils, light hydrocarbon compositions and biomarker maturity parameters, but are clearly distinguished from oils in the Kosei area, Akita Prefecture. Relative oil maturity among oils in the Amarume, Yurihara and Ayukawa fields varies depending on maturity parameters used. In addition to oil maturity, gas maturity and Bouguer anomaly map suggest that oil and gas generated in the center of depression near Sakata have migrated into the Amarume field.
