Effective and reliable reservoir monitoring is critically important for optimizing oil/gas production and ensuring safe geologic carbon sequestration. It requires an optimal sensor deployment that uses a minimum number of sensors to record the most significant information resulting from reservoir property changes. Conventional monitoring survey designs are typically based on seismic-wavefield illumination analyses, which cannot alone determine the best receiver locations for effective and reliable monitoring of reservoir property changes. We propose a new approach for designing seismic monitoring surveys by analyzing the sensitivities of elastic waves with respect to reservoir geophysical property changes. The method is based on differentiating the elastic-wave equations with respect to geophysical parameters. The resulting sensitivity equations are solved simultaneously with the elastic-wave equations using a finite-difference scheme. Numerical studies confirm that time-lapse seismic survey designs based on elastic-wave sensitivity analysis can be totally different from those based on elastic-wavefield illuminations. For time-lapse seismic monitoring, receivers should be placed at locations where elastic-wave sensitivities are significant. Modeling of elastic-wave sensitivity propagation provides a fundamental tool for effective seismic monitoring survey designs.
We review recent advances in the area of composite sandwich modeling, sensitivity analyses, optimization techniques and applications, with the focus on structuralacoustic problems. The optimization of sandwich structures is with respect to passive design parameters, such as material constants, geometric parameters, cellular core geometry and boundary conditions.
The purpose of this research is to design optimal boundary supports for minimum structural sound radiation. The influence of the boundary conditions on the structural dynamics of a cantilever beam is first examined to motivate the research. The boundary supports constraining both the in- and out-of-plane degrees of freedom of the plate are considered as the design parameters. The fixed and free boundary degrees of freedom are represented by a continuous function with the help of homogenization. Analytical expressions of sensitivity functions are employed in the optimization, leading to more efficient and accurate numerical solutions. The sensitivity expressions are based on the linear equation system obtained with the finite element method. Numerical examples of single frequency and broadband optimizations are presented. The sensitivity of the optimal design parameters with respect to small random perturbations is also studied. The examples demonstrate that an encouraging reduction of sound radiation as measured by the mean square normal velocity can be achieved with the optimal boundary conditions as compared with the base line structure.
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