ABSTRACT

Based on a large quantity of laboratory ultrasonic measurement data of sedimentary rocks and using Monte Carlo simulation and Backus averaging, we have analyzed the layering effects on seismic anisotropy more realistically than in previous studies. The layering effects are studied for different types of rocks under different saturation conditions. If the sedimentary strata consist of only isotropic sedimentary layers and are brine-saturated, the δ value for the effective transversely isotropic (TI) medium is usually negative. The δ value will increase noticeably and can be mostly positive if the sedimentary strata are gas bearing. Based on simulation results, c13 can be determined by other TI elastic constants for a layered medium consisting of isotropic layers. Therefore, δ can be predicted from the other Thomsen parameters with confidence. The theoretical expression of δ for an effective TI medium consisting of isotropic sedimentary rocks can be simplified with excellent accuracy into a neat form. The anisotropic properties of the interbedding system of shales and isotropic sedimentary rocks are primarily influenced by the intrinsic anisotropy of shales. There are moderate to strong correlations among the Thomson anisotropy parameters.

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