Southwestern Part of Mt. Chookai where is covered with its lavas and detritus, has been explorated by geophysic methods and wells these few years. Results of exploration are outlinedin followings;
(1) Oil accumulation and reservoir conditions in Fukra field were controlled by sea bottom high which had existed during Tentokuji grey mudstone depoisted.
(2) At Masukawa, Katsurane alternated facies quickly change its thickness from north to south. It is presumable that warping or arching actions occurred in late Tentokuji in this district.
(3) From studies of stratigraphic sections, it is reasonably expected that oil have accumulated in Katsurane formation at Higashi-Fukura, westside of Masukawa, and in Katsurane, Funakawa and Onnagawa formations near nakamura, eastside of Masukawa.
