Improving the Image Quality of High-Angle Interfaces and Subsalt Sediments Using High-Order Scattered Seismic Waves

摘要

High-angle or steeply-dipping faults, salt flanks, and subsalt sediments are important structures for many applications such as oil/gas and geothermal energy exploration. However, conventional seismic imaging has poor illuminations in these areas because of using singly scattered waves or primary reflections. By using high-order scattered waves in the reverse time migration (RTM), particularly the secondary scattered waves, we can enhance the seismic illumination for imaging the steep faults and subsalt areas. In our method, we first identify reflection features such as geological layer boundaries and discontinuities, based on the conventional RTM images. We then modify the migration model by adding potential point scatterers into the reflection features. These artificial point scatterers could be randomly placed on and around the reflection features to illuminate the structures where primaries cannot reach. The random placement of the point scatterers differentiates our method from previous methods using duplex or prism waves to image high-angle structures where true reflector locations are particularly identified. In addition, we assign the artificial point scatterers as density perturbations without modifying the velocity model so that they do not affect the spatial position of the imaged reflectors. The proposed method of high-order scattering imaging only requires one additional implementation of RTM but can substantially improve the image quality around high-angle faults and subsalt regions. We verify the effectiveness of our method using two synthetic models, a trapezoidal model and the Sigsbee2B model. And the results demonstrate that our new method produces better images for steep faults and subsalt areas compared with those obtained using conventional RTM.