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Anisotropic elastic least-squares reverse time migration with density variations in vertical transverse isotropic media

Zhong Yu, Gu Hanming, Liu Yangting, Luo Xia, Mao Qinghui, Xu Kai

Acta Geophysica

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2024

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Vol. 72, no. 1

67--83

EN

Elastic least-squares reverse time migration (ELSRTM) has the potential to provide higher-quality migration images related to the lithology and fluid by imaging multi-component seismic data than conventional elastic reverse time migration (ERTM). Oil and gas are widely stored in fractures and sedimentary rocks. The sedimentary rocks and the rocks with fractures will produce anisotropy. The anisotropy effect should be corrected in migration. In order to correct the anisotropic effect to the images of ELSRTM, a new anisotropic ELSRTM scheme is developed to image the multi-component seismic data in vertical transverse isotropic (VTI) media. This new ELSRTM method can invert high-quality images and correct the anisotropic effect in VTI media. Many ELSRTM methods assume that the density is constant. However, the constant-density assumption will generate false migration results when the density of media is variation. We derive the elastic VTI de-migration operator in the media with density variations based on Born approximation. The adjoint state equations and gradient formulas with respect to medium images in VTI media with density variations are also derived by the adjoint state method. Using the new elastic de-migration operator, adjoint state equations, and gradients in VTI media with density variations, we can produce high-resolution subsurface elastic reflectivity images. Numerical examples from the graben VTI model and modified HESS VTI model demonstrate that the proposed ELSRTM can not only generate the images with high quality but also correct the anisotropic effect in VTI media with density variations.

2

Effect of Variable-Density and Constant-Density Representations of Flow on Simulating Terrestrial Groundwater Discharge into a Coastal Lagoon

Al-Taliby Wissam, Dekhn Hadeel

Journal of Ecological Engineering

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2021

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Vol. 22, nr 11

188--197

EN

Terrestrial groundwater discharge (TGWD) can be an important pathway for pollutants into coastal water bodies. Thus, a reliable way to quantify it is essential for efficient coastal management practices. This study evaluated the feasibility of using constant-density models for estimating TGWD amounts into the Indian River Lagoon, which is a variable-density estuarine environment. Constant-density models were developed using MODFLOW, while variable-density models were developed using SEAWAT. The numerical models were calibrated to match the field measured head data under the lagoon. The amounts of TGWD into the IRL and hydraulic head distributions calculated by the two codes were compared over eight pairs of numerical experiments. Two of those numerical experiments used the calibrated model and field measured conditions, while the rest of them used modified versions of the calibrated models, including variable anisotropy ratio k, variable lagoon salinity LS, and increased water table elevation by 5%. The results showed that the constant-density model is fairly accurate in estimating TGWD and head distributions at the calibrated k in the range of 1000–20,000 with an error not exceeding 9.4% under the actual measured field conditions. Even when LS was assumed to increase to ocean salinity value of 1.0, a case that rarely occurs in IRL, the calibrated constant-density model’s accuracy was not affected substantially. However, the constant-density model failed to represent the physics of the variable-density environment at k values lower than 1000, where the error exceeded 129%. Generally, the accuracy of the constant-density model was found to increase substantially at lower LS and higher water table elevations.

3

Surface waves in non-homogeneous, general magnetothermo, viscoelastic media of higher order

Sethi M., Gupta K. C., Rani M.

International Journal of Applied Mechanics and Engineering

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2013

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Vol. 18, no. 4

1221--1236

EN

The aim of the present paper is to investigate surface waves in a non-homogeneous, isotropic, visco-elastic solid medium of n-th order including the time rate of strain. The theory of generalised surface waves has firstly been developed and then it has been employed to investigate particular cases of waves, viz., Stoneley, Rayleigh and Love type. The wave velocity equations have been obtained for different cases and are in well agreement with the corresponding classical result, when the effects of viscosity, temperature, magnetism as well as nonhomogeneity of the material medium are ignored.