基于三相Biot速度应力波动方程的水合物储层波场数值模拟

Numerical simulation of hydrate reservoir based on three-phase Biot velocity-stress wave equaiton

天然气水合物储层可以看作由骨架、水合物和孔隙水构成的三相孔隙介质。以三相Biot一阶速度应力波动方程作为声波在水合物储层传播的控制方程,用有限差分法(FDTD)进行数值模拟。波场快照可以清楚展现3个纵波和两个横波,与Biot理论相符。根据实测速度优化控制方程参数,使数值速度与实测速度相符。结果表明:孔隙度对水合物剪应力分量影响最显著,对水合物、孔隙水和骨架速度分量的影响次之,所以储层中孔隙度最适合用水合物剪应力分量来分析。骨架速度分量和应力分量受饱和度的影响较小,水合物剪应力分量受饱和度的影响最大,所以分析储层中水合物饱和度的最佳选择是水合物剪应力分量。

Natural gas hydrate reservoirs are considered as three-phase porous media,comprising skeleton,hydrate,and pore water.Utilizing the three-phase Biot first-order velocity stress wave equation as the governing equation for sound wave propagation in gas hydrate reservoirs,numerical simulations are conducted employing the finite difference time domain(FDTD) method.The wavefield snapshots vividly illustrate three compressional waves and two shear waves,consistent with Biot's theory.Through parameter optimization of the control equation based on measured velocities,numerical velocities are aligned with measured velocities.The results highlight porosity as the most influential factor on the shear stress component of gas hydrates,followed by impacts on hydrates,pore water,and skeleton velocities.Consequently,porosity is best analyzed using the shear stress component of gas hydrates in reservoirs.The skeleton velocity and stress components are less affected by saturation,while the shear stress component of gas hydrates is most affected.Therefore,the optimal choice for analyzing gas hydrate saturation in reservoirs is the shear stress component of gas hydrates.