新潟地域における深部探鉱

Abstract

MITI* & METI* wells in the Niigata basin have been providing invaluable data to consider the conditions of future potential hydrocarbon traps in the deeper part of the basin. In the MITI-Niigata Heiya well, the large amount of core data provided rock properties which are required to consider the standard lithostatic pressure of the basin. The results of the MITI-Mishima well gave us useful indicators concerning maturity level of source rocks as well as realization of difficulties to interpret seismic sections of steep folded zone. The MITI-Higashiyama well, which was drilled in the western part of the Higashiyama anticline, showed the existence of faulted block structures below the thick and steep surface limb. Various in-situ stresses were measured in the METI-Niitsu well to take advantage of the rock mechanics techniques in petroleum geology. Using the MITT & METI wells together with the other wells drilled by private oil companies, this paper presented some assumptions in order to discuss the seal potential, the structural analysis and the fracture distributions in the deeper part of the Niigata basin. Attractive seal potential areas were presumed by superimposing the thicker areas of Teradomari Formation and the comparatively thinner distribution areas of agglomerates in Shiiya-Nishiyama Formations. Breakout analysis, fault pattern analysis of regional outcrops as well as Green-Tuff horizons and lost-mud phenomenon in wells indicate that the sub-surface structuring was controlled by the echelon faults which were constructed by sinistral strikeslip movements. The different ways of fracture development in acidic rock and in mafic rock of the deeper part of the basin support the idea that the ductility contrast of rocks, creates the environment in which remnant stress and the distribution of natural fractures are controlled in deep-sited condition. *MITI: The Ministry of International Trade and Industry, **METI: The Ministry of Economy, Trade and Industry