Seismic dispersion and attenuation in layered rocks with random orthogonal fractures
As a channel for fluid flow,fractures that are widely distributed in the formation determine the effective permeability of the formation.As a result,the detection of the fractures has a significant impact on the exploration and development of oil and gas.Seismic survey is a common means of detecting the fractures.When seismic waves propagate in the saturated layered porous rocks with intersecting fractures,wave-induced fluid flow can occur between the adjacent layers(interlayer flow),between the fractures and the background pores(FB-WIFF),and within the intersecting fractures(FF-WIFF).Fluid flow inside the rocks makes the elastic parameters of the rocks vary with frequency that accompanies the energy loss,leading to the dispersion and attenuation of seismic waves.This paper develops theoretical models for the dispersion and attenuation of the elastic parameters of layered porous rocks with random orthogonal fractures under the joint influence of interlayer flow,FB-WIFF and FF-WIFF,and analyses the influencing factors and rules of the dispersion and attenuation of the elastic parameter C33.The results show that the dispersion and attenuation of C33 in the interlayer flow stage are directly related to the difference in the elastic moduli between the two adjacent layers.When there is no difference in the elastic moduli between the two adjacent layers,C33 does not disperse and attenuate,and the dispersion and attenuation of C33 are enhanced with the increase of the difference in the elastic moduli between the two adjacent layers and with the decrease of the difference in the layer thickness between the two adjacent layers.The dispersion and attenuation of C33 in the FB-WIFF and FF-WIFF stages are mainly affected by the background pore aspect ratio,background porosity,fracture aspect ratio and fracture density of each layer,in which the dispersion and attenuation of C33 in the FB-WIFF stage are enhanced with the increase of the background pore aspect ratio,the background porosity,the fracture density,and the decrease of the fracture aspect ratio,respectively.The dispersion and attenuation of C33 in the FF-WIFF stage are highlighted with the increase of the background porosity and fracture density and the decrease of the background pore aspect ratio and fracture aspect ratio,respectively.This study improves our understanding of the seismic wave dispersion and attenuation in layered porous rocks with random orthogonal fractures,and provides theoretical support for the quantitative evaluation of the fractured rocks using seismic survey data.
万方数据
维普
