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

拟议的项目旨在开发一种新的方法，通过补充使用地球化学模型和实施地震建模和反演的有效介质理论来量化大陆边缘沉积物中的天然气水合物(GH)数量。反射地震利用偏移速度分析(MVA)提供关于P波层速度变化的二维信息，该信息将被反演以确定原位GH浓度。相比之下，数值模型将提供可靠的甲烷和生长激素形成潜力的预测，当根据来自ODP点的地球化学数据进行校准时。初步结果表明，用地震方法预测天然气储量对准确确定孔隙度具有很高的敏感性。这可能会造成很大的不确定性，可以通过对照数值模式进行校准来减少这种不确定性。基本战略是使用地球化学法作为对ODP点附近的地球物理模型的基本参数的约束。反过来，经过良好校准的地球物理模型将沿着地震线提供有用的模型输入，在这些地震线上没有钻井数据可用于地球化学建模。这一方法将产生关于区域变量(例如沉积物厚度、热流、降解常数)的可靠信息，可用于对GH库存和分布进行经验预测。此外，将针对高流量情景(例如泥火山)进行选定的关键研究，以改进对其在全球气候变化总存量中所占比例重要性的估计。

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.