Detection of gas-saturated and fractured reservoirs by anelastic absorption

Abstract

Fluid saturation and fracture density are key phenomena that determine the quality factor of carbonate reservoirs, and both of them are directly linked to high anelastic absorption of seismic waves. This study estimated the quality factor (Q-value) from seismic reflections by using a tomographic inversion algorithm based on the frequency shift method, which was implemented in the CAT3D software. This tool adopted a modified version of the minimum-time ray-tracing method and the simultaneous iterative reconstruction technique algorithm for the inversion. The frequency analysis was done for the reference pulse and targeted wavelet, which was essential for estimating the Q factor accurately. The Q tomography result provided a macro-model to estimate the anelastic absorption, i.e., the low-frequency spatial component. A new algorithm is adopted for computing the instantaneous frequency. It is based on Ackroyd's theorem, which links the centroid of the instantaneous spectrum of a wavelet to the instantaneous frequency. The algorithm provided by Poggiagliolmi and Vesnaver (2014) is more stable and reliable than those ones available in some popular commercial or public-domain software. This allows improving the computation of the instantaneous frequency. Applying the pre-stack migration to the instantaneous frequency to convert it from time to depth domain, followed by a derivative, I get the high-frequency component of the Q factor. The final anelastic absorption result is obtained by combining the instantaneous frequency micro-model with the Q-tomography macro-model in the depth domain. Such a broadband estimate may benefit reservoir characterization and monitoring.

Date of Award	Dec 2016
Original language	American English
Supervisor	Aldo Vesnaver (Supervisor)