南海北部陆坡水合物勘探区典型站位不同类型热流对比

随着南海北部陆坡天然气水合物勘探工作的深入开展,在南海北部陆坡天然气水合物勘探区典型的集中了钻孔、探针和BSR三种测量方式获得的热流数据.为了解海底热流不同测量方式的差异,以及南海北部陆坡水合物勘探区的热流特征,文章以SH-2和SH-5孔作为典型站位,分别介绍三种热流测量方法并对两个站位的不同类型热流进行对比分析,结果表明:(1)在SH-2孔处探针热流与钻孔热流基本一致,但在SH-5孔处探针热流明显低于钻孔热流;采用钻孔实测沉积物平均热导率计算的SH-2和SH-5两个站位处的BSR热流都与相应钻孔热流基本一致.(2)根据地震剖面及相邻位置探针热流特征分析,SH-5站位处探针热流明显偏低,可能是受到流体活动的影响.(3)相对SH-2孔,SH-5孔具有较高的地温梯度和热流特征,可能是SH-5钻孔未钻到水合物的重要原因,而晚期泥底辟侵入可能是造成SH-5孔具有较高的温度场并导致原本赋存的水合物分解的原因.

Comparison of different-type heat flows at typical sites in natural gas hydrate exploration area on the northern slope of the South China Sea

In the natural gas hydrate exploration on the northern slope of the South China Sea,three types of heat flow data were derived from drilling measurement,probe measurement,and BSR measurement.To investigate the differences of different seafloor heat flow measurement methods and the characteristics of natural gas hydrate exploration area on the northern slope of the South China Sea,the paper takes SH-2 and SH-5,the two wells for natural gas hydrate exploration,as the typical sites to describe the three heat flow measurement methods and compare the results at the two sites.The following results were gotten.First,the probe-type heat flow is almost identical with drilling-type heat flow at Site SH-2,but is lower obviously at Site SH-5;BSR-type heat flows calculated with actual average heat-conductivity are almost identical with drilling-type heat flows at both Site SH-2 and Site SH-5.Second,the obviously lower probe-type heat flow than drilling-type heat flow at Site SH-5 might be caused by liquid activities,as indicated by analysis of the characteristics of seismic profile and heat flow of neighboring sites.Third,the Site SH-5 has higher geothermal gradient and heat flow than Site SH-2,which may be an important reason of failure to get hydrate at Site SH-5.Furthermore,it may be the late-stage diapir that brought higher temperature and decomposed the former hydrate at Site SH-5.