南海北部渗漏型水合物成藏系统的发育特征及其形成演化规律  

Developmental characteristics and evolution of seepage gas hydrate accumulation system in the northern South China Sea

作　　者：陈雨核 任金锋[2] 李廷微 徐梦婕 王笑雪 廖远涛 CHEN Yuhe;REN Jinfeng;LI Tingwei;XU Mengjie;WANG Xiaoxue;LIAO Yuantao(College of Marine Science and Technology,China University of Geosciences(Wuhan),Wuhan 430074,China;National Engineering Research Center of Gas Hydrate Exploration and Development,Guangzhou Marine Geological Survey,Guangzhou 511458,China)

机构地区：[1]中国地质大学(武汉)海洋学院,湖北武汉430074 [2]广州海洋地质调查局天然气水合物勘查开发国家工程研究中心,广东广州511458

出　　处：《地学前缘》2025年第2期77-93,共17页Earth Science Frontiers

基　　金：国家重点研发计划项目(2021YFC2800901);国家自然科学基金项目(42376221,42276083);广州海洋地质调查局局长科研基金项目(2023GMGSJZJJ00030);广东省基础与应用基础研究重大项目(2020B0301030003);中国地质调查局二级项目(DD20230064)。

摘　　要：渗漏型水合物成藏系统往往发育中高饱和度的水合物及其下伏伴生气,是海域广泛分布的一类水合物资源,也是海底灾害、冷泉系统和气候变化的重要研究对象。因此,认识其分布规律和形成机制具有重要意义。本文通过南海北部海底观测、岩心、测井、地震及测试分析资料,系统总结了渗漏型水合物成藏系统发育的地貌、地质、地球物理与地球化学方面的识别标志,发现渗漏型水合物主要分布在渗漏通道内。按照渗漏通道形成的机械失稳方式不同将其分为两类:构造圈闭控制的水力破裂型渗漏通道,呈集群状分布;高角度断层控制的剪切破裂型渗漏通道,呈线状分布。在渗漏型水合物成藏系统中,深部气体沿气烟囱、断层等运移并聚集在甲烷水合物稳定带底部附近。当流体压力大于上覆细粒沉积地层的破裂力时,游离气向上突破形成渗漏通道,在渗漏通道内的高角度裂隙网中形成中高饱和度裂隙充填型水合物,在穿越的薄砂层中形成高饱和度孔隙充填型水合物。游离气在渗漏通道内的长距离运移过程可能受到3种机制的影响,即排盐效应维持的热力学三相平衡、水合物壳的形成使得甲烷扩散受限和高甲烷通量导致的水合物动力学生长速率受限。与活动冷泉相关的渗漏型水合物的形成过程可划分为3个阶段:(1)盖层破裂阶段。在超压作用下可能受水合物动力学生长速率的影响;(2)向上突破阶段。局部升高的盐度和温度维持了热力学三相平衡;(3)当流体到达海底后,地温趋近背景值,进入稳定渗漏阶段。排盐效应和水合物壳导致的甲烷扩散受限控制了水合物的生成。当冷泉停止活动后,盐度随着游离气的不断扩散而降低,渗漏通道的底部逐渐有新的水合物再次形成。Seepage gas hydrate accumulation systems tend to develop medium-to-high saturation gas hydrates and their associated underlying gases,which are widely distributed gas hydrate resources in the ocean.These systems are also important research subjects for submarine disasters,cold seep systems,and climate change.Therefore,understanding their distribution patterns and formation mechanisms is of great significance.Based on seafloor observations,core samples,well logging,seismic data,and test analysis from the northern South China Sea,this study systematically summarizes the geomorphological,geological,geophysical,and geochemical indicators for identifying seepage gas hydrate accumulation systems.The findings reveal that seepage gas hydrates are primarily distributed within escape pipes.Escape pipes can be categorized into two types based on their mechanical failure mechanisms:(1)hydraulic fracturing escape pipes controlled by structural traps,which exhibit clustered distributions,and(2)shear failure escape pipes controlled by high-angle faults,which show aligned distributions.In seepage gas hydrate accumulation systems,deep gas migrates and accumulates near the bottom of the methane gas hydrate stability zone along gas chimneys and faults.When fluid pressure exceeds the fracturing strength of the overlying fine-grained sedimentary layer,free gas breaks through upward to form escape pipes.This process results in medium-to-high saturation fracture-filling gas hydrates within high-angle fracture networks in the escape pipes and high-saturation pore-filling gas hydrates in thin sand layers intersected by the pipes.The long-range migration of free gas within escape pipes is influenced by three mechanisms:(1)thermodynamic three-phase equilibrium maintained by salt exclusion,(2)methane diffusion limited by the formation of gas hydrate shells,and(3)gas hydrate kinetic formation rates constrained by high fluid fluxes.The formation process of seepage gas hydrates associated with active cold seeps can be divided into three stages

关 键 词：渗漏型水合物 渗漏通道 机械失稳 长距离运移 南海北部 

分 类 号：P618.13[天文地球—矿床学]