Abstract
Reservoir parameter estimation is one of the goals of amplitude-versus-angle (AVA) inversion and angle-domain common image gathers are the basis of AVA inversion. Therefore, the accuracy of kinematic and kinetic information on angle gathers is very important for reservoir characterization. Reverse time migration is one of the most physically accurate migration method. Generating angle gathers from reverse time migration with the Poynting vector method is very efficient. However, due to inaccurate angle measurement and uneven illumination, angle gathers calculated by the Poynting vector method are often not suitable for AVA inversion. In this paper, we propose an efficient method of angle gathers with accurate angular information and amplitude from reverse time migration. We firstly decompose source and receiver wavefield to their up-going and down-going parts by using analytic wavefield. We calculate propagation directions for source down-going wavefield and receiver up-going wavefield by the Poynting vector method and form the angle gathers with these angle information and decomposed wavefield. To reduce memory storage and improve computational efficiency, we decompose wavefield at excitation amplitude time by using a local spatial Fourier transform. We also use a spatial smoothed Poynting vector to improve the stability of angle measurement. We apply an illumination compensation image condition to recover the true amplitude. Numerical examples on Marmousi model and the SEAM two-dimensional (2D) model demonstrate the advantages of our proposed method. The angle gathers based on our method are cleaner with more focus on events energy and better continuity, suffering from less low-frequency noise in the shallow parts and with a distinct cutoff at large angle where reflection terminates. At last, we demonstrate the effectiveness of proposed method on a 2D marine field data example.
Highlights
The technology of amplitude versus angle (AVA) has been widely used to estimate subsurface petrophysical properties and predict fluid in the reservoirs for decades [1,2,3]
We propose a new method to generate angle gathers under the reverse time migration frame, in which the angle information is calculated by a hybrid method
A simple We twocalculate layer model is shown in Figure to with compare different angle measurement anglewhich gathers of one point (x = 31a km) one shot (x = 2.4 km)
Summary
The technology of amplitude versus angle (AVA) has been widely used to estimate subsurface petrophysical properties and predict fluid in the reservoirs for decades [1,2,3]. The input data for AVA analysis are angle gathers which are generated during the seismic migration process. Traditional approaches of calculating angle gathers are commonly implemented in ray-based migration methods since the ray-based propagator naturally provides angle information. The ray-based methods are limited by the high-frequency asymptotic approximation [4,5], the wave equation based methods [6] were adopted for the angle gathers calculation. As the wave equation-based methods do not provide propagation direction explicitly, several methods were proposed to extract angle information from wavefield. These methods can be Energies 2020, 13, 6204; doi:10.3390/en13236204 www.mdpi.com/journal/energies
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