A model to predict the elastic properties of gas hydrate-bearing sediments

A simple and accurate model for predicting the elastic properties of gas hydrate-bearing sediment (GHBS) is proposed and validated against experimental data. It is developed on the basis of the homogenization theory for multi-phases composite. Unlike the classical homogenization techniques those fix a homogenization scheme (e.g. self-consistent, Mori-Tanaka, DEM, etc.) for a given microstructure, the proposed model considers a flexible homogenization scheme that adapts with the change of the microstructure of the material. The idea is to modify the elastic properties of the reference matrix with respect to the microstructure change of the mixture. Such modification is ensured by adapting the theoretical method to available experimental data. The derived method is proved to be very powerful as it can fit laboratory measured data on gas hydrate-bearing sand formed by different methods including excess gas and excess water methods and log data taken from various sites. Such feature cannot be satisfied by the existent models those consider the hydrate phase as a cement phase or a pore-filling phase. A very good agreement between the proposed method and experimental data offer a simple and accurate ways to predict the saturation of gas hydrate using sonic log data or 3D seismic data.

本研究提出了一款用于预测含天然气水合物沉积物（gas hydrate-bearing sediment, GHBS）弹性特性的简洁精准模型，并通过实验数据完成了模型验证。该模型基于多相复合材料均匀化理论构建。与传统均匀化技术不同——传统技术会针对特定微观结构固定采用某一均匀化方案（例如自洽模型、Mori-Tanaka模型、DEM模型等），本模型采用了可随材料微观结构变化自适应调整的柔性均匀化方案。其核心思路为：根据混合体系的微观结构变化，对参考基体的弹性特性进行修正。该修正过程通过将理论方法适配现有实验数据得以实现。经推导得到的本模型具备极强的适用性，可拟合不同制备方法（包括过气法、过水法）得到的含天然气水合物砂岩实验室实测数据，以及多类勘探区块的测井数据。仅将水合物相视为胶结相或孔隙充填相的现有模型，均无法实现这一特性。本模型与实验数据间具备极佳的吻合度，可为利用声波测井数据或三维地震数据预测天然气水合物饱和度提供简洁精准的技术途径。