Attenuation Compensation in Least-Squares Reverse Time Migration Using the Visco-Acoustic Wave Equation
King Abdullah University of Science and Technology
Fluids trapped in overburden structures cause strong attenuation of P-waves which hamper the resolution of migrated images. If the attenuation is too strong, ignoring it during migration can lead to incorrect positioning of reflectors below these layers. Attenuation of P-waves can be quantified by a quality factor, Qp, which accounts for the amplitude attenuation and the phase shift as a function of the frequency content of the propagating waves and the distance travelled. Lower values of Qp imply very high attenuation. The values of Qp for rocks like gas-sandstone and shale are very low which necessitates the need to account for Qp during migration for more accurate images.
Reverse time migration has become the standard migration algorithm for imaging in complex geological settings. Acoustic reverse time migration uses the two-way wave equation for computing the Green’s functions and is more accurate than the integral based Kirchhoff methods. Least-squares reverse time migration can mitigate the artifacts of standard reverse time migration and can produce images of better resolution during the linearized inversion process. However, both of the methods do not implicitly take into account the attenuation effect due to Qp if the standard acoustic wave equation is used for wavefield extrapolation. I use the visco-acoustic wave equation instead of the standard acoustic wave equation and show with numerical tests that least-squares reverse time migration using the linearized visco-acoustic wave equation can compensate for the attenuation loss and can produce images with better balanced amplitudes and accurate positioning of reflectors.
AAPG Search and Discovery Article #90182©2013 AAPG/SEG Student Expo, Houston, Texas, September 16-17, 2013