新潟県南部基礎試錐による頸城地域の地化学的評価

根源岩と油•ガスの性状について

抄録

Two stratigraphic test wells, the MITI Takadaheiya and the MITI Kashiwazaki Oki, were drilled in the southwestern part of Niigata prefecture during the 6th term of MITI's Five-Year Plan. Geological studies were made in the Kubiki area using analytical data of above wells and the Kubiki Oil Field.
It is known that thick alternations of sandstone and mudstone from the Nanatani stage to the Lower Teradomari stage, so-called the “Nambayama Facies”, are distributed in the Kubiki area, of which facies are confirmed of existence in the above two wells. However, in the MITI Naoetsuoki Kita, which was located in the offshore Naoetsu, the Nambayama Facies mentioned above are changed into mudstone facies at the Nanatani stage.
The MITI Takadaheiya shows that the top of oil window is about 1, 800m in depth and the gradient of maturity is very large. The source rock of the Kubiki Oil Field has not specified in the section of Kubiki area yet: therefore, the oils are assumed to have come from the northern or eastern part of the areas where kerogens are expected to be matured.
The MITI Kashiwazaki Oki indicates that the top of oil window is about 2, 200m in depth and the gradient of maturity is very gentle as compared with the MITI Takadaheiya. Mudstones in the Nanatani stage are correlated to oils obtained from the Shiiya formation by the biomarker and carbon isotope data. It is interpreted that the oils have moved from the Nanatani formation to the Shiiya formation through thrust faults formed in the middle of Nishiyama age.