Development of a combined geochemical-geophysical approach for quantification of regional submarine gas hydrate inventories

该项目旨在开发一种新的方法，通过互补使用地球化学模型和有效介质理论（EMT）进行地震建模和反演，来量化大陆边缘沉积物中天然气水合物（GH）的数量。反射地震利用迁移速度分析（MVA）提供了纵波层速度变化的二维信息，这些信息将被反转以确定原位GH浓度。相比之下，当与ODP地点的地球化学数据进行校准时，数值模型将提供可靠的甲烷和天然气形成潜力预测。初步结果表明，地震方法预测天然气储量对孔隙度的准确测定具有很高的敏感性。这可能会造成很大的不确定性，可以通过对数值模型进行校准来减少不确定性。基本策略是使用地球化学方法作为ODP地点附近地球物理模型基本参数化的约束。反过来，一个校准良好的地球物理模型将沿着地震线提供有用的模型输入，在没有钻井数据的地方进行地球化学建模。这种方法将产生关于区域变量（例如，沉积物厚度、热流、退化常数）的可靠信息，这些信息可用于对全球暖储量和分布的经验预测。此外，将对高通量情景（例如泥火山）进行选定的关键研究，以改进对其对全球植被总量的比例重要性的估计。

The proposed project aims at developing a new approach to quantify the amount of gas hydrate (GH) in continental margin sediments by the complementary use of geochemical models and the implementation of the effective medium theory (EMT) for seismic modelling and inversion. Reflection seismics provides 2-D information on variations in P-wave interval velocities using migration velocity analysis (MVA), which will be inverted to determine in situ GH concentrations. In contrast, numerical models will provide reliable predictions of the formation potential of methane and GH when calibrated against geochemical data from ODP sites. Preliminary results show that the prediction of GH inventories by seismic methods is highly sensitive to the accurate determination of porosities. This may cause large uncertainties, which can be reduced by calibration against the numerical model. The basic strategy is to use the geochemical approach as constraint for basic parameterisations of the geophysical model in the vicinity of ODP sites. In turn, a well-calibrated geophysical model will then provide useful model inputs along seismic lines where no drilling data are available for geochemical modelling. This approach will yield solid information on regional variables (e.g. sediment thickness, heat flow, degradation constants), which can be used for empirical predictions of the GH inventory and distribution. In addition, selected key studies will be performed for high flux scenarios (e.g. mud volcanoes) to improve estimates of their proportional significance for the total GH inventory.