西南太平洋天然气水合物形成与分布的地热背景

GEOTHERMAL BACKGROUND FOR GAS HYDRATES FORMATION AND DISTRIBUTION IN THE SW PACIFIC REGION

天然气水合物广泛分布于海底和永久冻土带。自20世纪末以来,新西兰北岛东坡希古朗基陆架和澳大利亚新喀里多尼亚盆地相继被科学家发现了天然气水合物标志BSR(BottomSimulatingReflector),这引起世界广泛关注,文章结合以前的研究工作,从地热角度剖析天然气水合物赋藏状况。依据国际热流委员会(IHFC)提供的西南太平洋地热数据,经过统计确定出该区域的热流分布;计算得出该区域热流平均值为80.1mW/m2,低于全球大洋边缘盆地地区平均热流值101±2.2mW/m2;结合天然气水合物温压方程,计算结果表明西南太平洋天然气水合物稳定带厚度平均值为274±20m,薄于其他已经发现的海洋天然气水合物稳定带平均厚度(约400m)。文章还定量分析了温度参数对天然气水合物稳定带的影响。

Gas hydrates are distributed widely in marine sediments and permafrosts. Since the end of last century, the existence of prominent hydrate-linked BSRs in both the Hikurang Margin off the east coast of the New Zealand＇s North Island and the Australian New Caledonia Basin has been conformed and were followed by great concerns from all over the world. With the previous research advancements about gas hydrates in the SW pacific region, we explored the thermal data provided by International Heat Flow Committee （IHFC） to analyze the occurrence of marine gas hydrates. Geothermal data in the SW Pacific region displayed the heat flow pattern. After we properly handled the data through applied statistics, 129 heat flow station measurements showed that the average heat flow in the region studied is 80.1mW/m^2, which is lower than the average heat flow of global oceanic basins （101±2.2mW/m^2）. By using phase equilibrium diagram, the thickness of gas hydrates stability zone （GHSZ） was calculated. Results exhibited that average thickness of the GHSZ in the region is 274±20m, which is thinner than that of the GHSZ （about 400m） in other sites of natural gas hydrates occurrence in the world. The effect of temperature parameter on GHSZ is also discussed in this paper.