基于等效介质理论的天然气水合物岩石物理建模方法

Rock physics modeling method of natural gas hydrate based on equivalent medium theory

地震岩石物理建模是将地震信息(地球物理观测值)定量转化为物性信息的桥梁,合理的水合物岩石物理模型可为开展水合物地层地震响应特征分析、饱和度预测、叠前地震反演提供理论基础,但水合物微观赋存方式存在多样性,它既可以作为骨架,又可以作为孔隙填充物存在于地层中,因而具有不确定性。为此,基于等效介质理论,在考虑水合物剪切性质的同时,构建水合物同时赋存于孔隙和基质时的岩石物理模型,将这种水合物的微观赋存模式表达成动态形式,通过实测纵波速度作为约束,以达到不断更新水合物存在于基质和孔隙中的比例的目的。利用某海域SH2井的实测资料验证了模型的合理性,该方法可为水合物地层的横波速度等物性参数预测提供技术支持。

Seismic rock-physics modelling is a bridge used to quantitively convert observed seismic information into the physical properties of reservoir.A reasonable rock-physics model is an important theoretical basis for seismic response analysis,saturation prediction and pre-stack seismic inversion of gas hydrate reservoir.However,gas hydrate can be either a part of rock matrix or a pore-filler,and this complicated composition may cause uncertainty and errors.Based on the equivalent medium theory,this paper presents a rock-physics model,which considers the shear modulus of hydrates and hydrates stored in pores and matrix at the same time.Particularly,the ratio between hydrates stored in pores and matrix is dynamic and can be updated by an iterative process constrained by Pwave velocity form well logging data.This model can be used to support for the prediction of S-wave velocity and saturation in gas hydrate layers,and has been validated by real logging data from well SH2 in a sea area.