海域天然气水合物岩石物理建模方法

海域天然气水合物赋存于疏松沉积物中，天然气水合物岩石物理建模之前需要建立疏松沉积物的岩石物理模型。为此，针对传统疏松沉积物岩石物理模型存在横波速度估计误差偏高、建模过程不自洽的问题，考虑海水对沉积物颗粒的润滑作用，引入改进的Hertz-Mindlin方程进行岩石物理建模，提高了建模精度；针对疏松沉积物的建模过程，首先利用改进的Hertz-Mindlin方程计算临界孔隙度条件下沉积物的弹性模量，然后利用Hashine-Shtrikman界限计算疏松沉积物骨架的弹性模量；在讨论不同赋存形态的水合物对沉积物弹性性质的影响及适用模型、判别准则的基础上，针对以颗粒支撑和孔隙流体充填两种赋存状态存在的天然水合物，设计了兼容两种赋存形态的岩石物理建模方法和流程。浅钻井的实测曲线与建模结果吻合度高，证实了该方法的适用性。

Petrophysical modeling for offshore natural gas hydrates

As offshore natural gas hydrates occur in unconsolidated sediments,the petrophysical model of unconsolidated sediments should be built before the petrophysical modeling of natural gas hydrates. The traditional petrophysical model of unconsolidated sediments,however,faces the pro-blems of a high error in the estimation of shear wave velocity and a non-self-consistent modeling process. Taking account of the lubrication effect of brine on sediment particles,this study introduces the modified Hertz-Mindlin equation in the mode-ling process to improve accuracy. During the mo-deling of unconsolidated sediments,the modified Hertz-Mindlin equation is used to calculate the elastic moduli of sediments under critical porosity,and then Hashine-Shtrikman bounds are applied to calculate the elastic moduli of the skeleton of unconsolidated sediments. Furthermore,this paper discusses the influence of different occurrence forms of hydrates on the elastic properties of sediments,as well as the applicable models and discrimination criteria. On this basis,for natural hydrates existing as supporting grains and pore-filling fluids,the petrophysical modeling method and process that suits the two occurrence forms are designed. The modeling results are highly consistent with the measured curves of shallow drilling,which verifies the applicability of this method.