Saturation effects on frequency-dependent seismic anisotropy in fractured porous rocks

Abstract

The response of Earth materials to seismic wave propagation is the most commonly used geophysical method for studying the Earth’s crust. Rocks making up the Earth’s crust are porous, with fluids occupying the pore space. The saturation of the pore space can be multiphase, for example, in gas reservoirs and gas bearing oil reservoirs where gas and liquid occupy the pore space. Additional voids such as aligned fractures are common in the Earth’s crust and are known to cause seismic anisotropy. Knowledge of the effects of pore fluids and of aligned fractures on seismic wave propagation is needed for the interpretation of seismic data in terms of these physical properties. This information is particularly useful for the hydrocarbon industry as the presence of either natural or artificially induced fractures can play a major role in the safe and efficient exploration and production of hydrocarbons. Therefore, it is important to be able to remotely characterise fractures in fluid-filled reservoir rocks.

Theoretical models are used to relate seismic measurements to the physical properties of rocks such as porosity, saturation, and fracture properties. Previous studies have either focused on multiphase saturation effects in non-fractured isotropic rocks or on single fluid phase saturation effects in fractured anisotropic rocks. Therefore, the combined effect of multiphase saturation and aligned fractures is still poorly understood. This thesis focuses on improving the understanding of the effect of saturation on fracture-induced seismic anisotropy

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