Time-Lapse Inversion of Velocity and Q Factor

Abstract

Abstract Rock properties play a crucial role in influencing the propagation of seismic waves within the Earth, providing valuable insights into various aspects such as the presence of hydrocarbons, porosity, saturation, and permeability variations. Seismic imaging serves two main purposes: mapping the heterogeneity of underground reservoirs and monitoring recovery processes on-site (Nur, 1989). Over time, both production and injection activities alter the response of the reservoir. Time-lapse (or 4-D) seismic monitoring is an essential tool for reservoir management, enabling the tracking of displacement processes. Changes in seismic properties, such as velocity and quality factor Q, can offer quantitative estimates of fluid changes. Some rock properties related to fluid saturation in the reservoir, such as anelastic absorption quantified by the quality factor Q, can undergo more significant changes than others, such as oil and gas mixed with brine or CO2. To estimate the quality factor Q from seismic reflections, we utilize a tomographic inversion algorithm based on the frequency shift method (Quan and Harris, 1997). This algorithm generates a macro-model for anelastic attenuation. In order to enhance resolution and obtain a micro-model, Poggiagliolmi and Vesnaver (2014) propose a new algorithm that is stable and reliable for computing the instantaneous frequency, which represents the centroid of the instantaneous spectrum. This algorithm improves the stability of calculating the instantaneous frequency and provides a high-resolution image of anelastic absorption. By utilizing this approach, the resulting broadband image of anelastic absorption in depth can offer superior monitoring of reservoir changes compared to conventional methods.