Time of Oil and Gas Accumulation in the Nigabo Oil Field

Abstract

In this paper, the writer discusses the time of oil accumulation in the Nigabo oil field. At Kotaki and Kamihama pools of this field, oil accumulated at about the time of the folding of pre-Sasaoka stage. Even though oil had once accumulated to form pools, a greater part of it was driven out of them by erosion, while oil accumulated almost concurrently with the folding of the last tectonic phase of the Shibikawa stage at Innai and Katsurazaka of the same field.Investigation into oil and gas accumulation in the Nigabo oil field arrives at the conclusion that the time of structural movement is another factor which controlled the oil accumulation. The reservoirs in the Funakawa formation at Innai pool is one of such examples. Even though these reservoirs were folded with black shale, oil could not accumulate in them, because the folding was too late to make an oil pool.