天然气水合物区多相流体运移模型：以南海神狐海域为例

Modeling Multiphase Flow and Transport of Gas Hydrate Zones: A Case Study from the Shenhu Area of the South China Sea

天然气水合物是重要的海洋油气资源,近年来利用孔隙水地球化学手段结合流体反应运移模型对水合物进行勘探已成为研究热点。文章针对南海神狐海域钻探GMGS-1航次的数据资料,用孔隙水溴碘摩尔数比值拟合全新世流体运移速率,构建了二期次非稳态水合物多相流体运移模型,并以SH7站位作为应用,发现自更新世以来研究区水合物成藏系统处于衰退状态。通过模型参数敏感性分析,了解到影响模型输出的参数权重从高到低依次是沉积物孔隙度、有机质含量和沉积埋藏速率。进一步数值分析表明,在水合物成藏系统中,有机质含量与水合物饱和度满足线性相关,其他主要参数与饱和度的关系并非单调函数,且主导水合物稳定区内的甲烷物源是深部外源流体所携带的甲烷。多相流体运移模型对水合物资源勘查具有一定的理论意义。

Gas hydrates are one of the significant offshore petroleum resources.The exploration of hydrates using combined porewater geochemistry and fluid reaction-transport modelling has become an important proxy in researches of recent years.Based on the data of GMGS-1 drilling project from the Shenhu area of the South China Sea,the advection velocity of porewater during the Holocene was fitted by the molar ratio of bromine to iodine,and a two-stage non-steady state multiphase fluid transport model of the gas hydrate zone was constructed.We found that the hydrate accumulation in the study area,i.e.Site SH7,was in decline since the Pleistocene.Through sensitivity analysis of model parameters,it was learned that the parameter weights affecting the output were sediment porosity,organic matter content and sediment burial rate in descending order.Further numerical analysis shows that in the hydrate accumulation system,hydrate saturation is proportional to organic matter content,but shows a non-monotonic dependence on other main parameters.Besides,it is the external methane from deep below dominates the methane source in the hydrate stability zone.The multiphase fluid transport model of this study provides theoretical basis for the exploration of hydrate resources.