Abstract:Porous and fractured reservoirs can be studied using effective medium theory in seismic low frequency. Fluid saturated porous media with a set of aligned fractures, which is known as Gurevich's model, can be expressed by combing linear-slip model and anisotropic Gassmann's fluid substitution theory. Fractures in Gurevich's quasi-static porous fractured model cannot be simply characterized by normal and tangential weaknesses, and the compliance matrix for the saturated porous fractured medium cannot be represented by the sum of an isotropic matrix and an excess compliance matrix with normal and tangential components. So we propose to use general fracture weaknesses to characterize parallel fractures, which are filled with fluids and hydraulically connected with surrounded pores. We investigate the characterization of general fracture weaknesses and analyze effects of fracture density, fluid infill, and equant porosity on general fracture weaknesses. The investigation shows that general fracture weaknesses are related to the fracture density, fluid saturation, and hydraulic connection between fractures and equant pores. In order to estimate the general fracture weaknesses from seismic data, we express linear reflection coefficients with general fracture weaknesses using Born formula. To understand how the general fracture weaknesses affect PP-reflection coefficients, we investigate the sensitivity of reflection coefficients to general fracture weaknesses. The general fracture weakness turns out to be suitable to characterize saturated fractures with porous isotropic background, and to quantitatively interpret seismic data.
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