ABSTRACT: Integrated multi-dimensional basin modeling in the Naoetsu Basin, Japan

Okui, Akihiko¹, Masahiro Kida², Tomohisa Nishizuka², Seiji Okamoto²
(1) Japan National Oil Corporation, Chiba, Japan
(2) Idemitsu Oil and Gas Co., Ltd, Tokyo, Japan

The Naoetsu Basin is located in the southern margin of Japanese oil and gas provinces. Oil and gas are mainly produced from the upper Miocene turbiditic sandstones in the onshore area.

Biomarks and carbon isotope data suggest that the oils were generated from the source rocks deposited in marine siliciclastic environment. The dominance of oleanane suggests higher plant input as well as higher maturity of the oils, which is the unique feature comparing with the oils in other Japanese basins. Carbon isotope data also suggest that the gas is thermogenic origin. The analysis of the rocks reveals that these oils are correlated with the middle Miocene shales, which have TOC=1-2% and hydrogen Index=200-400 mgHC/gTOC.

JNOC's SIGMA-2D basin modeling indicates that the oil generation occurred from the Pliocene age. The gas generation has just started in the deepest part of the basin. To calibrate thermal history, we used the FAMM-derived vitrinite reflectance data, since ordinary data appears to be suppressed. The suppression reaches 0.5% reflectance at peak oil generation.

Since the time after the generation is very short, the migration must be efficient to have oil and gas accumulations. The 2D basin modeling indicates that the vertical migration to the upper Miocene and Pliocene sandstones is quick through the tectonic fracture zones in conjunction with the structuring since the Pliocene age. The migration efficiency (accumulation/generation ratio) is about 1% based on the evaluation by 3D ray-trace method.

AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia