メタンハイドレート探査手法とその基本コンセプト

抄録

Methane hydrates, which are ice like materials and constructed with methane and water molecules, are spread widely under permafrost and deep water areas. It is thought that methane hydrates are ones of occurrence type of methane and can be future energy resources.
BSR (bottom simulating reflector) occurs at the basement of GHSZ (gas hydrate stability zone) and therefore it is used to detect occurrences of methane hydrates in deep waters using reflection seismic data. At the same time, BSR is only the first step for methane hydrate exploration because BSR does not provide information about thickness, saturation and type of methane hydrate bearing zone. From the viewpoint of resource exploration, practical methods to analyze details of methane hydrate resource fields have been required.
We constructed an effective strategy to delineate methane hydrate concentrated zones, of which reservoir are turbidite sand bodies, utilizing four following indicators in 3D seismic data: (A) BSR, (B) turbidite sequence (above BSR), (C) strong seismic reflectors and (D) relatively higher interval velocity, suggesting methane hydrate concentrated sand layers. It enabled us to delineate methane hydrate concentrated zones and evaluate their rock volume successfully in the eastern Nankai Trough as similar as prospects and leads in conventional oil and gas fields are delineated by geological and geophysical approaches.