Geomorphological-geological-geophysical signatures of high-flux fluid flows in the eastern Pearl River Mouth Basin and effects on gas hydrate accumulation  

作　　者：Zenggui KUANG Yunxin FANG Jinqiang LIANG Jing'an LU Lei WANG 

机构地区：[1]Key Laboratory of Marine Mineral Resources, Ministry of Land and Resources,Guangzhou Marine Geological Survey [2]New Energy Project Department, China National Petroleum Corporation Offshore Engineering Company Limited

出　　处：《Science China Earth Sciences》2018年第7期914-924,共11页中国科学（地球科学英文版）

基　　金：supported by the National Natural Science Foundation of China (Grant No. 41406068)

摘　　要：Marine hydrate reservoirs can be divided into focused high-flux and distributed low-flux gas hydrate systems according to free gas migration control mechanisms. In focused high-flux hydrate reservoirs, fluids easily break through the pressure of overlying sediments and reach the shallows, creating a series of geomorphological-geological-geophysical anomalies at and near the seafloor. Based on detailed interpretation of pre-drilling data in the eastern Pearl River Mouth Basin(PRMB),many anomalies related to the high-flux fluid flow are found, including seafloor mounds with intrusive characteristics, bright spot reflections above the bottom-stimulating reflector(BSR), phase reversals in the superficial layer, and an efficient fluid migration and accumulation system composed of fractures and uplifts. The second hydrate drilling expedition was carried out in the eastern PRMB in 2013 to study these anomalies. The acquired data show that high-flux fluid flow occurred in these sites. Gas hydrate pingoes, bright spot reflection above the BSR, and an efficient fluid migration and accumulation system can be used as identification signatures for high-flux fluid migration. The modes of high flux fluid flow are different in deep and shallow sediments during upward migration of fluid. Gas dissolved within migrating water dominates deep fluid migration and upward migration of a separate gas phase dominates the shallow process. This difference in migration models leads to formation of upper and lower concentrated hydrate reservoirs in the drilling area. The discovery of signatures of high-flux fluid flow and their migration modes will help with site selection and reduce risk in gas hydrate drilling.Marine hydrate reservoirs can be divided into focused high-flux and distributed low-flux gas hydrate systems according to free gas migration control mechanisms. In focused high-flux hydrate reservoirs, fluids easily break through the pressure of overlying sediments and reach the shallows, creating a series of geomorphological-geological-geophysical anomalies at and near the seafloor. Based on detailed interpretation of pre-drilling data in the eastern Pearl River Mouth Basin（PRMB）,many anomalies related to the high-flux fluid flow are found, including seafloor mounds with intrusive characteristics, bright spot reflections above the bottom-stimulating reflector（BSR）, phase reversals in the superficial layer, and an efficient fluid migration and accumulation system composed of fractures and uplifts. The second hydrate drilling expedition was carried out in the eastern PRMB in 2013 to study these anomalies. The acquired data show that high-flux fluid flow occurred in these sites. Gas hydrate pingoes, bright spot reflection above the BSR, and an efficient fluid migration and accumulation system can be used as identification signatures for high-flux fluid migration. The modes of high flux fluid flow are different in deep and shallow sediments during upward migration of fluid. Gas dissolved within migrating water dominates deep fluid migration and upward migration of a separate gas phase dominates the shallow process. This difference in migration models leads to formation of upper and lower concentrated hydrate reservoirs in the drilling area. The discovery of signatures of high-flux fluid flow and their migration modes will help with site selection and reduce risk in gas hydrate drilling.

关 键 词：Eastern Pearl River Mouth Basin Gas hydrate High-flux fluid flow Geomorphological-geological-geophysicalsignatures 

分 类 号：P618.13[天文地球—矿床学]