Cenozoic tectonic settings and a current exploration concept in southern central Hokkaido, northern Japan.

要旨

The Yufutsu oil and gas field, Tomakomai City, southern Ishikari Plain, centralHokkaido, has its naturally fractured reservoir in Cretaceous granitoids and overlying Eoceneconglomerates, which form a large horst-complex delineated by normal faults. Stratigraphic andstructural features of the Yufutsu field and its surrounding areas indicate that prominentextensional deformation shaped the horst during the late Oligocene to early Miocene, when the lateCenozoic sedimentary basin in the southern Ishikari Plain originated and subsequently developedstepwise from an extensional-transtensional (?), relatively localized basin to a transpressionalforeland basin of a regional scale. Understanding of these Cenozoic tectonic processes leads to anexploration concept which counts basement horsts for traps with fractured reservoir and deeplyburied coal-bearing strata for hydrocarbon sources. The MITI Umaoi well, drilled 25km north ofthe Yufutsu field, proved this concept practical even in a subthrust setting, as it hit a wellpermeable fractured reservoir within a basement horst. A new lithostratigraphic unit, Minami-naganuma Formation (Upper Oligocene), is formally proposed.

主題