基于天然气水合物地震数据计算南海北部陆坡海底热流

Estimation of the Heat Flow in the Northern of the South China Sea Based on the Seismic Data of Gas Hydrate

天然气水合物是一种由水的冰晶格架及其间吸附的气体分子 (以甲烷为主 ) 组成的固态化合物, 地震剖面上的似海底反射BSR是天然气水合物赋存的重要地球物理标志。相同气体成分水合物的相对稳定的温压关系是根据BSR的赋存深度计算海底热流的理论基础。选择南海北部陆坡有典型BSR反射的地震剖面, 计算了南海北部陆坡天然气水合物发育区的压力、温度、地温梯度、热导率及热流等地热参数。通过计算热流值与实测热流值的对比可以大致推测,在南海北部陆坡海底运用该方法计算的热流值误差可能在 12%以内。本研究不仅可以为海底热流等理论研究提供一定信度的数据资料, 而且通过实测热流值校正后的热流数据以及经验公式, 可以反过来用于BSR深度的计算以及天然气水合物稳定域的预测, 具有重要的实践意义。

Gas hydrates are ice-like crystalline substances composed of cages of water molecules that host low molecular weight gases mainly methane. Bottom simulating reflector (BSR) in seismic profile is an important seismic indicator for existence of gas hydrates.Because gas hydrates which have different component have relatively stable relationships of temperature and pressure respectively, pressure, temperature and even heat flow in gas hydrate stability zone can be estimated based on the data of existence of gas hydrates consequently. Using the calculating method mentioned above, typical seismic profiles in the northern of the South China Sea, where BSR can be recognized obviously, were chosen to calculate these geothermal data. The contrast between the calculated values and the measured values show that the calculated error can be limited in 12%.To a certain (extent),estimation of the heat flow from seismic data of gas hydrate can provide reliable data of heat flow for (academic) research; Furthermore, the data of heat flow and the experiential formula which were calibrated by measured values of heat flow can be used to predict the depth of BSR and the thickness of gas hydrate stability zone.