ABSTRACT: Tectonic Framework and Hydrocarbon Potential of the Back-arc Basins in Northwestern Japan

TSUJI, KOHSUKE, Idemitsu-Oil Development Co., Ltd., Tokyo, Japan

Evolution of the back-arc basins of northeastern Japan is greatly related to the opening of the Sea of Japan, which is believed to have occurred during the period from 19 to 15 Ma based on the results of the Ocean Drilling Program and paleomagnetic data. The opening may be different from the continental break up in the Atlantic in style, as no clear mid-ocean ridge exists and several trends of extensional grabens were formed and filled by extensive volcanic rocks early on. The orientations of these grabens are generally parallel to the today's coast line.

Sedimentation of deep marine fine clastics with good source potential followed in these grabens during Middle to Late Miocene. An increase of turbidite input to the grabens in Early Pliocene may indicate an onset of conversion tectonics from the pull apart in Early to Middle Miocene to ongoing east-west compression. As the axis of the compression varies from perpendicular to the preexisting grabens in Akita to diagonal in Niigata, structural style also varies.

Main reservoirs of oil and gas fields in the area are fractured submarine volcanic rocks of Middle Miocene and turbidite sands of Pliocene. Predicting good quality reservoir is a key issue in both plays. Genetic facies and rock properties as well as diagenesis are controlling factors in volcanic reservoirs, whereas rapid lateral facies change and contamination of fine tuff are main difficulties in turbidite reservoirs. Maturation, timing of generation and entrapment and seal are also critical problems.

AAPG Search and Discovery Article #91015©1992 AAPG International Conference, Sydney, N.S.W., Australia, August 2-5, 1992 (2009)