Influence of patchy saturation on seismic dispersion and attenuation in fractured porous media. Issue 1 (19th April 2018)

• Record Type: Journal Article
• Authors: Zhang, Jinwei; Huang, Handong; Wu, Chunhua; Zhang, Sheng; Wu, Gang; Chen, Fang
• Is Part Of: Geophysical journal international. Volume 214:Issue 1(2018:Jul.)
• Page Start: 583
• Page End: 595
• Publication Date: 2018-04-19
• Subjects: Fracture and flow -- Seismic anisotropy -- Seismic attenuation -- Wave propagation; Geophysics -- Periodicals; 550
• DOI: 10.1093/gji/ggy160
• Languages: English
• ISSNs: 0956-540X

Abstract

SUMMARY: Wave-induced fluid flow due to mesoscopic heterogeneity can explain seismic dispersion and attenuation in the seismic frequency band. The mesoscopic heterogeneity mainly contains lithological variations, patchy saturation and mesoscopic fractures. The patchy saturation models which are locally based on Biot theory for porous media have been deeply studied, but the patchy saturation model for fractured porous media is rarely studied. In this paper, we develop a model to describe the poroelastic characteristics in fractured porous media where the background and fractures are filled with different fluids based on two scales of squirt flow. The seismic dispersion and attenuation in fractured porous media occur in two scales, the microscale due to fluid flow between pores and microcracks and mesoscale due to fluid flow between background and heterogeneities. We derive the complex stiffness tensor through the solution of stress equivalence and fluid conservation. Two new parameters embodying the fluid effects are introduced into the model compared with the single fluid phase model. The model is consistent with Gassmann–Wood equation at low-frequency limit and consistent with the isolated fracture model at high-frequency limit. After the frequency-dependent stiffness tensor is obtained, the variations of velocities and inverse quality factors with frequency are analysed through several numerical examples. We investigated three poroelastic cases: medium including pores and microcracks; media including pores, microcracks and fractures; media including pores and fractures. The frequency-dependent characteristics of patchy saturation model are different with those of single fluid model not only in characteristic frequency but also in the magnitude of the attenuation. Finally, we discuss the results obtained and the special case where the fractures are saturated with gas or dry and the background is filled with water. We also compare our results with those of patchy saturation model and double porosity model. The results will contribute to the actual exploration work to a certain extent, such as the fluid identification in fractured reservoirs.