Research teams from Hokkaido University and Ibaraki University have found that carbonate concretion, which is widely distributed around the Izura coast in Kitaibaraki City, Ibaraki Prefecture, leaked from a deep underground oil and gas field about 1,650 million years ago. It was clarified that the gas was chemically changed and formed.
The Izura coast is a scenic spot with strange rocks and reefs.The reef consists of hard lumpy and layered sedimentary rocks made of carbonate concretion (calcium carbonate-based rock mass).It is thought to be derived from methane associated with cold spring water on the seafloor, but the origin and origin of methane were unknown.
The research team observed samples taken from carbonate concretions, measured gas components, measured residual gas and isotope compositions of carbonates, and anaerobic methane-oxidized archia (paleobacteria) involved in chemical changes in methane. Molecular fossils were analyzed.As a result, it was found that most of the carbonate carbon was derived from natural gas, and bicarbonate ions generated from methane, which is a natural gas component, combined with calcium ions in seawater to form carbonate concretion.
About 1650 million years ago, crustal movements caused cracks in oil and gas fields on the seabed, and natural gas continuously spouted for tens of thousands of years.The volume of carbonate formed as a result is more than 600 million cubic meters, which is one of the largest in the world.Since only a part of the natural gas that springs to the seabed forms carbonate, the amount of natural gas that is actually washed away is enormous.This indicates that there was an oil and gas field (recoverable reserves of 950 billion cubic meters or more) comparable to a huge gas field in the Izura area.It is said that crude oil also existed in the phantom "Izura oil and gas field", and the possibility that oil and natural gas resources existed off the coast of Ibaraki Prefecture increased at once.
From 2019, Japan's new XNUMXD geophysical exploration vessel "Tansa" will carry out underground resource exploration in the waters around Japan.Off the coast of Ibaraki Prefecture is also an important survey target, and future progress is expected.
