Zhang, Y.; Di, B.; Gao, F.; Li, L. Effects of Background Porosity on Seismic Anisotropy in Fractured Rocks: An Experimental Study. Appl. Sci.2023, 13, 8379.
Zhang, Y.; Di, B.; Gao, F.; Li, L. Effects of Background Porosity on Seismic Anisotropy in Fractured Rocks: An Experimental Study. Appl. Sci. 2023, 13, 8379.
Zhang, Y.; Di, B.; Gao, F.; Li, L. Effects of Background Porosity on Seismic Anisotropy in Fractured Rocks: An Experimental Study. Appl. Sci.2023, 13, 8379.
Zhang, Y.; Di, B.; Gao, F.; Li, L. Effects of Background Porosity on Seismic Anisotropy in Fractured Rocks: An Experimental Study. Appl. Sci. 2023, 13, 8379.
Abstract
Fractures are present in hydrocarbon reservoirs of different porosity ranges. Seismic anisotropy has been widely used in fracture characterization and shown to be sensitive to background matrix porosities in theoretical studies. An understanding of the effects of background porosity on seismic anisotropy could improve seismic characterization in different fractured reservoirs. Based on synthetic rocks with controlled fractures, we conducted laboratory experiments to investigate the influence background porosity has on P wave anisotropy and shear wave splitting. A set of rocks containing the same fracture density (0.06) with varying porosities of 15.3%, 22.1%, and 30.8% were constructed. P and S wave velocities were measured at 0.5 MHz as rocks were water saturated. Results show that when porosity increased from 15.3% to 22.1%, P wave anisotropy and shear wave splitting exhibit slight fluctuations. However, when porosity continued to increase to 30.8%, P wave anisotropy declined sharply while shear wave splitting stayed nearly constant. The measured results were compared with predictions from equivalent medium theories. Qualitative agreements were found between theoretical predictions and measured results. In Eshelby-Cheng model, the increase of porosity reduces the fracture-induced perturbation in the fracture normal direction, resulting in a lower P wave anisotropy. In Gurevich(2003) model, the increase of porosity can reduce the compressional stiffness in parallel direction to a larger extent than that in perpendicular direction, thus leading to lower P wave anisotropy.
Keywords
Anisotropy; Fractures; Porosity; Rock physics
Subject
Environmental and Earth Sciences, Geophysics and Geology
Copyright:
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