摘要
从勘探技术和资源评价的角度综述了甲烷水合物生成和聚集的重要特征 ,如地震反射剖面、测井曲线资料、地球化学特点等以及对未知区的地质勘探和选区评价。甲烷水合物在地震剖面上主要表现为BSR(似海底反射 )、振幅变形 (空白反射 )、速度倒置、速度—振幅结构 ( VAMPS)等 ,大规模的甲烷水合物聚集可以通过高电阻率 ( >1 0 0欧姆·米 )声波速度、低体积密度等号数进行直接判读。此项研究实例表明 ,沉积物中典型甲烷水合物具有低渗透性和高毛细管孔隙压力特点 ,地层孔隙水矿化度也呈异常值 ,并具有各自独特的地质特征。现场计算巨型甲烷水合物储层中甲烷资源量的方法可分为 :测井资料计算法公式为 :SW=( ab Rw/m· Rt) 1/ n;地震资料计算法公式为 :ρp=( 1 - ) ρm+ ( 1 - s) ρw+ sρh、VH=λ··S。对全球甲烷水合物总资源量预测的统计达 2 0× 1 0 15m3 以上。甲烷水合物形成需满足高压、低温条件 ,要求海水深度 >30 0 m。因此 ,甲烷水合物的分布严格地局限于两极地区和陆坡以下的深水地区 ,并具有 3种聚集类型 :1 .永久性冻土带 ;2 .浅水环境 ;3.深水环境。深海钻探计划 ( DSDP)和大洋钻探计划 ( ODP)已在下述 1 0个地区发现大规模的甲烷水合物聚集 ,他们是 :秘鲁、哥斯达黎加、危地马拉、?
Gas hydrates have significant characteristics which are easily used to determine their accumulation through the appearances on marine seismic reflection profiles,the changes of well logs and geochemical features etc. The main appearances of gas hydrates in the seismic reflection profiles are the bottom simulating reflections(BSR),reduction of amplitude (amplitude blanking),velocity inversion and Velocity and Amplitude Structures(VAMPS).Large amount of gas hydrate accumulation can be detected from high resistivity(usually>100 Ω·m),sonic velocity,low volumetric density and so forth.Direct measurement of samples of gas hydrates indicates that sediments which typically host gas hydrates have low permeability and high capillary entry pressure and that salinity of pore water in gas hydrate strata is abnormal.The use of seismic data is an important way to calculate the quantity of in situ gas hydrates in a large gas hydrate reservoir.Using the well log data is another useful way to estimate the bulk volume of gas hydrates.The in situ methane quantities in a large gas hydrate reservoir can be directly measured through the Pressure Core Samples(PCS).In China offshore seas,mainly in South China Sea and East China Sea,obvious signs of hydrates have been distinguished in seismic reflection profiles,and high temperature of seawater and high ratio of methane in fluids can be observed.All these signs and observations indicate that it is completely possible there exists a large amount of gas hydrates in China offshore seas.
出处
《海洋地质与第四纪地质》
CAS
CSCD
北大核心
2000年第1期63-72,共10页
Marine Geology & Quaternary Geology
基金
Financed by State Natural Foundation!(No.4973 2 0 0 5 )
