台西南盆地含天然气水合物沉积层测井响应规律特征及其地质意义

The characteristics of logging response of the gas hydrate formation in Taixinan Basin and its geological significance

文章分析了台西南盆地渗漏型和扩散型天然气水合物沉积层的测井曲线特征,并通过对比DSDP 84航次570号钻孔含天然气水合物层段测井资料,结合研究区的区域地质条件、水合物饱和度、钻井岩心资料以及地震反射剖面特征,总结出台西南盆地天然气水合物沉积层的测井响应规律及其地质意义,结果表明:研究区含水合物沉积层的测井曲线有高电阻率、高声波速度、高中子孔隙度、低补偿密度和低自然伽马的"三高两低"的异常特征,渗漏型水合物层测井曲线"三高两低"特征较扩散型明显,渗漏型水合物沉积层内水合物碳氢气体浓度高,在断层通道内高度聚集形成块状水合物,水合物的饱和度最高达到100%,水合物分解后形成碳酸盐层,部分碳氢气体沿裂隙向上运移后再次形成的水合物层,扩散型水合物主要分布在水合物稳定带的底部,水合物呈分散状存在于沉积物中,水合物分布范围较大,气体容积扩散,碳氢气体浓度下降,水合物的最高饱和度为31%,水合物气源主要为微生物成因气,裂解气可能以生物降解气的形式与微生物气为水合物的形成共同提供气源。研究区断层、断裂和气烟囱等构造发育,地震反射剖面上具有似海底反射(BSR)、振幅空白带、BSR与地层斜交、穹状反射(速度振幅异常而形成的眼球状结构)等水合物响应特征。

This paper analyzes the logging curve feature of the sediments with seepage gas-hydrate and diffuse gas-hydrate of Taixinan Basin,compared with the logging data of gas hydrae formation at Site 570 of DSDP84.In combination with regional geological conditions,hydrate saturation,drilling core data and the characteristics of seismic reflection profile,the logging response characteristics of gas hydrae formation and its geological significance in Taixinan Basin were summed up.The results show that the log of the hydrate bearing sediments have the anomalous characteristics of＂three high,two low＂,i.e.,high resistivity,high acoustic velocity,high neutron porosity,low compensated density,and low natural gamma,and the anomalous characteristics of seepage gas-hydrate is more obvious than that of diffuse gas-hydrate;that seepage gashydrate has high concentration of hydrocarbon gas,and the gas accumulated and formed massive gas hydrate in the fault passage,the saturation of gas-hydrate up to 100%,the hydrates formed carbonate after decomposition,and part of the hydrocarbon gas moved upward along fissures and formed gas-hydrate again;that the diffuse gas-hydrate is mainly distributed in the bottom of the hydrate stability zone,and distributed in disperse states in strata,the distribution range of the diffuse gas-hydrate is much bigger,gas volume spread,hydrocarbon gas concentration declined,and the highest saturation up to 31%;that the gas source of hydrate is bacterial gas,pyrolysis gas（in the form of biodegradation gas）combined with the bacterial gas providing the gas source for the formation of gas hydrate.There are faults,fractures,gas chimney structures,etc.developed in the study area,and there are BSR,amplitude blank tape,BSR oblique crossing strata and＂augen＂phenomenon in the seismic profile.