晚期泥底辟控制作用导致神狐海域SH5钻位未获水合物的分析  

Analysis of Gas Hydrate Absence Induced by the Late-stage Diapir Domination in the Borehole SH5 of Shenhu Area

作　　者：王力峰[1] 沙志彬[1] 梁金强[1] 陆敬安[1] 

机构地区：[1]广州海洋地质调查局,广东广州510760

出　　处：《现代地质》2010年第3期450-456,共7页Geoscience

基　　金：国家重点基础研究发展计划项目(2009CB219508);国土资源部公益性行业科研专项项目(200811014)

摘　　要：海底泥底辟构造与天然气水合物成藏关系密切,泥底辟既能为水合物提供充分的气源物质,同时又能促使地层温度场改变进而影响水合物成藏稳定性。南海北部神狐海域SH5站位虽然BSR明显,但钻探证实不存在天然气水合物。该钻位温度剖面异常高,温度场上移,同时在其下伏地层中发现泥底辟构造和裂隙通道。根据上述事实并结合泥底辟发育各个阶段中的特点,认为泥底辟构造对天然气水合物成藏具有控制作用。泥底辟发育早期和中期阶段,低热导率和低热量有机气体有利于天然气水合物生成;而在晚期阶段,高热量液体上侵稳定带底界,导致水合物分解迁移。SH5站位很可能由于受到处于晚期阶段的泥底辟上侵而未能获取天然气水合物。There is a close relationship between mud diapirs and occurrences of gas hydrates in the marine sediments.While mud diapirs provide gas hydrates with abundant source material,they control gas hydrates occurrences by disturbing the thermal field.Borehole SH5 located in the Shenhu working area in the northern South China Sea shows a clear BSR in the seismic profile,but it turns out to be a sediment lack of gas hydrates by the evidence of borehole sampling.The thermal field moves upwards with higher equilibrium temperatures in the borehole SH5 below which a mud diapir and associated faults are approaching.Based on the facts above and the mud diapir＇s evolution in each stage,a model is proposed that the occurrence of gas hydrates is very likely to be under the control of mud diapirs in this site.During the early and intermediate stages of mud diapir growth,organic gases with low thermal conductivity and low thermal energy are converted into gas hydrates at the bottom of gas hydrate stability zone.In the late stage of mud diapir growth,fluid with high thermal energy invading the bottom of gas hydrate stability zone,makes the gas hydrate disintegrated.Then the librated free gases will move along the sediment strata and be condensed into gas hydrates again when temperature and pressure favor their formation.The borehole SH5,probably too close to a late-stage mud diapir,captures no gas hydrate.

关 键 词：泥底辟 天然气水合物 神狐海域 南海 

分 类 号：P744.4[天文地球—海洋科学]