ODP/IODP典型水合物站位稳定带界限和水合物分布的地球化学识别标志

Geochemical indicators of the gas hydrate stable zone and its distribution in the typical drilling sites of ODP/IODP

本文采用ODP/IODP典型站位样品实测和相关数据搜集对比研究的方法,进行了多种游离烃甲烷及相关指标在水合物形成过程中的地质作用和地球化学特征研究,以及酸解烃甲烷与围岩组分和沉积中自生碳酸盐、浊积岩的关系及地球化学特征的研究,据此筛选出判识水合物稳定带(GHSZ)的地球化学标志。结果显示:(1)下伏地层中游离甲烷异常是天然气水合物稳定带孔隙中赋存动态甲烷的反映,由于指标测试方法和沉积物状态的差异,深部水合物稳定带上呈现出特定的两种游离烃甲烷指标HS和VAC正负拆离分隔的异常模式;(2)酸解烃与地层吸附甲烷能力和围岩组分性质密切相关,对应于水合物最佳赋存条件的自生碳酸盐和浊流岩,酸解烃甲烷具有显著的量化异常特征;(3)水合物形成过程中甲烷通量促进了甲烷厌氧氧化反应(AMO)和自生碳酸盐的生成。酸解烃甲烷与浅层自生碳酸盐具有显著的对应关系,弥补了浅部沉积中游离烃甲烷异常具多源和多解性的不足;(4)游离烃甲烷异常组合模式和酸解烃甲烷量化异常分布是GHSZ和有利水合物赋存条件的综合反映,能够为水合物稳定带和带内水合物聚集的判识提供依据。

We analyzed a number of samples from the typical drilling sites of ODP/IODP and by means of correlation of the collected data.We studied the geological process and geochemical characteristics in the formation of various free hydrocarbon and their relevant indicators,and studied the relationship between the acidolysis hydrocarbon,the composition of the surrounding rock,the authigenic carbonate during the sedimentation and the turbidite and the related geochemical features.Based on these,it provides us a new scientific method to find out the exact location of gas hydrate stable zone（GHSZ）.The results show that,（1）The free methane anomaly in the underlying formation reflects that there is dynamic methane in the pores of the gas hydrate stable zone.In the deep gas hydrate stable zone there are two types of specific models of free hydrocarbon index anomaly appeared due to the differences in testing methods and the state of sediments;（2）Acidolysis hydrocarbon is closely related to the methane adsorption ability of the formation and the componental properties of the surrounding rock.Corresponding to the best hydrate occurrence conditions of the authigenic carbonates and turbidites the relation of acidolysis hydrocarbon is characteristic of significantly quantified anomaly;（3）In the process of hydrate formation,methane flux promotes the anaerobic methane oxidation（AMO）and the formation of authigenic carbonates.The acidolysis hydrocarbon is prominently corresponding to the near-surface authigenic carbonate which makes up the deficiency of multiple sources and multiple solutions of free hydrocarbon methane anomaly in shallow sediments;（4）The anomaly patterns of free hydrocarbon methane and the quantitative anomaly distribution of acidolysis hydrocarbon methane are the comprehensive response for the GHSZ and the favorite occurrence conditions of hydrates and can provide the basis for the determination of the gas hydrate stable zone and the hydrate accumulation in the zone.