摘要：Seismic data from sedimentary rocks usually exhibits attenuation levels than can not be explained by existing theoretical models. An important dissipation mechanism for waves in heterogeneous poroelastic media is the effect of wave-induced fluid flow created by mesoscopic scale heterogeneities, known as mesoscopic loss. Mesoscopic length scales are those larger than pore size but smaller than wavelengths in the seismic range (1- 100 Hz). A typical mesoscopic heterogeneity has a size of tens of centimeters. Mesoscopic heterogeneities can be due to local variations in lithological properties or to patches of immiscible fluids. For example, a fast compressional wave traveling across a porous rock saturated with water and patches of gas induces a greater fluid pressure in the gas patches than in the water saturated parts of the material. This in turn generates fluid flow and slow Biot waves which diffuse away from the gas-water interfaces generating significant losses in the seismic range. In this work an iterative domain decomposition finite element procedure is presented and employed to solve Biot’s equations of motion for saturated poroelastic materials. The domain decomposition procedure is naturally parallelizable, which is a necessity in this type of simulations due to the large number of degrees of freedom needed to accurately represent these attenuation effects. The numerical simulations, run on a parallel computer, were designed to show the effects of the wave-induced fluid flow on the traveling waves in the seismic range of frequencies. The simulated recorded traces show evidence of the mesoscopic loss mechanism in this type of materials.
其他摘要：Seismic data from sedimentary rocks usually exhibits attenuation levels than can not be explained by existing theoretical models. An important dissipation mechanism for waves in heterogeneous poroelastic media is the effect of wave-induced fluid flow created by mesoscopic scale heterogeneities, known as mesoscopic loss. Mesoscopic length scales are those larger than pore size but smaller than wavelengths in the seismic range (1- 100 Hz). A typical mesoscopic heterogeneity has a size of tens of centimeters. Mesoscopic heterogeneities can be due to local variations in lithological properties or to patches of immiscible fluids. For example, a fast compressional wave traveling across a porous rock saturated with water and patches of gas induces a greater fluid pressure in the gas patches than in the water saturated parts of the material. This in turn generates fluid flow and slow Biot waves which diffuse away from the gas-water interfaces generating significant losses in the seismic range. In this work an iterative domain decomposition finite element procedure is presented and employed to solve Biot’s equations of motion for saturated poroelastic materials. The domain decomposition procedure is naturally parallelizable, which is a necessity in this type of simulations due to the large number of degrees of freedom needed to accurately represent these attenuation effects. The numerical simulations, run on a parallel computer, were designed to show the effects of the wave-induced fluid flow on the traveling waves in the seismic range of frequencies. The simulated recorded traces show evidence of the mesoscopic loss mechanism in this type of materials.
