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A 3-Dimensional Analysis and Assessment of the Natural Gas Hydrate System in the Kumano Forearc Basin, Offshore Japan, from NanTroSEIZE Drilling and 3D Seismic Data

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Title:A 3-Dimensional Analysis and Assessment of the Natural Gas Hydrate System in the Kumano Forearc Basin, Offshore Japan, from NanTroSEIZE Drilling and 3D Seismic Data
Authors:Taladay, Katie
Keywords:gas hydrates
Kumano Basin
heat flow
resource assessment
Date Issued:Aug 2015
Publisher:[Honolulu] : [University of Hawaii at Manoa], [August 2015]
Abstract:Natural gas hydrates are crystalline inclusion compounds that form within the pore space of marine sediments along continental margins worldwide. These hydrate deposits host highly compressed gas molecules, most commonly methane, and are proposed to be the largest dynamic reservoir of organic carbon on this planet. As such, it is tremendously important for both climate scientists and countries in need of energy security to understand the controls on hydrate formation, stability, and decomposition in response to natural and manmade environmental stresses. This study utilizes industry quality 3-dimensional (3D) seismic reflection data combined with Integrated Ocean Drilling Program (IODP) drilling data collected during the NanTroSEIZE project in the Kumano Forearc Basin, offshore Japan. Our aim is to investigate natural gas hydrate occurrence, the 3D distribution and behavior of the base of gas hydrate stability (BGHS) in response to surface and underlying deformation processes, fluid flow patterns, zones of concentrated hydrate deposits, and a gas in place resource estimate for hydrate concentration zones near the BSR.
Three types of BSRs including upper, lower, and a primary gas hydrate related BSRs were identified and mapped a across a region of 27 km by 11 km. The primary BSR, inferred to be the BGHS, is a widespread, continuous feature, and the depths of the primary BSR clearly show the complex controls that underlying basement deformation from compressional tectonics, and surface sedimentation and mass wasting events exert on the BGHS. Upper BSRs mark paleo-BGHS in the seaward regions, as well as the top of hydrate concentration zones above the BSR in two regions of the basin. Mixed gas, BGHS modeling provides compelling evidence that the lower BSRs could mark a Structure-II methane-ethane gas hydrate BGHS below a Structure-I methane hydrate BGHS. While 3D BSR-derived heat flow values were found to range from 42 -54 mWm-2 , which indicates that focused fluid advection is not presently active, drilling and seismic data provide evidence for thermogenic gas migration from depth up into basin sediments. Gas charged fluids are identified in the seismic data as high amplitude reflections (HARS) and low velocity zones beneath the BGHS, and migration appears to proceed as diffuse flow up landward dipping permeable strata, through short-range hydrate recycling in response to BGHS repositioning and up/laterally outward from deep cutting normal faults. Deep fluids potentially charge the four zones of concentrated gas hydrate deposits identified above the BSR. The hydrate concentration zones (HCZs) presented in this study are analogous to the confirmed methane HCZs in the eastern Nankai Trough, and should be considered highly prospective reservoirs.
Description:M.S. University of Hawaii at Manoa 2015.
Includes bibliographical references.
Appears in Collections: M.S. - Geology and Geophysics

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