Print this pageAAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Application of Illumination Compensation to Irregular Surface Areas Imaging
(1) PetroChina Hangzhou Research Institute of Geology, Hangzhou, China.
(2) Modeling and Imaging Laboratory, IGPP, University of California, Santa Cruz,, Santa Cruz, CA.
Lots of oil and gas reservoirs are located in the areas with irregular topography which offers a big challenge for traditional horizon-based depth migration algorithms in the mountain areas. The limited acquisition aperture widely exists in the real seismic acquisition system. It would be more serious in the area with irregular topography. Based on our previous study, in this paper, we have done some further study and analysis about acquisition-aperture correction to improve the image quality in irregular surface area.
Pre-stack depth migration turns out to be a valid way to get better image of these area. Migration with data acquired on surface with irregular topography can be extrapolated from the highest surface based on one-way wavefield propagator. We fill the area (fictitious layers) between the highest surface level and the irregular surface with near surface velocity. At every depth, the corresponding seismic data are added if receivers or source exist. Also, a filter was introduced to eliminate the migration noise in the fictitious layers. We use the local-cosine-bases (LCB) beamlet propagator which improves the image quality at the near irregular surface area because of its windowed reference velocity. We apply the local exponential frame (LEF) decomposition to obtain the image and amplitude correction factor in local wavenumber domain and then transform them into local angle domain after all the shot summation. The influence of irregular topography has been eliminated during the continuation process.
We test our method with Canadian overthrust irregular surface model (Model94) which has the highest elevation nearly 1800 meters. Compare with the imaging results without aperture correction and with Auto-vertical gain control (AGC), it has significant improvement in image quality, especially, the deep weak illumination area. Comparison about the amplitude versus angle (AVA) response before and after the acquisition aperture correction also shows the validity of our method.
Because of the local reference velocity used in beamlet propagation, the image near the irregular surface has some improvement. After the aperture correction, the image of deep weak illumination area became clearer. So,acquisition aperture correction can also be a good way for us to improve image quality in area with irregular topography.