Joint inversion of PP- and PS-waves based on the iteration of ratio of S-wave velocity and P-wave velocity
(2.Xinjiang Oilfield Company, PetroChina, Karamay, Xinjiang, China 834000)
【Abstract】If we do not have velocity information when extracting P-wave velocity, S-wave velocity, and density from EI (elastic impedance), k (ratio of S-wave velocity and P-wave velocity) is set to a constant, which is always different from real k. This assumption leads to errors in the inversion results. It is found that inversion of P-wave velocity, S-wave velocity, and density based on EI is unstable due to noise (lack of information of big incident angles). We analyze influences of k on inversion results by the parameter resolution matrix, and have found that P-wave velocity and density are hardly affected by k, and that S-wave velocity is very sensitive to k. Based on this point, we design a nonlinear k value iteration method to obtain first accurate k value, and then accurate S-wave velocity. Then we derive P-SV wave elastic impedance accurate (SEI) formula based on Aki-Richards P-SV wave reflection coefficient approximation formula. Finally we propose a joint iteration of k value to extract P-wave velocity, S-wave velocity, and density from EI and SEI. The proposed join inversion is tested on a four-layer model and Marmousi 2 model. The tests results show that k value can rapidly converge to its real value and inversed P-wave velocity, S-wave velocity and density are more accurate and stable.
【Keywords】 elastic impedance; parameter resolution matrix; shear wave velocity; k value iteration; joint inversion;
Connolly P. Calibration and inversion of non-zero offset seismic. SEG Technical Program Expanded Abstracts, 1998, 8: 182-184.
Connolly P. Elastic impedance. The Leading Edge, 1999, 18(4): 438-452.
Lu S M, McMechan G A. Elastic impedance inversion of multichannel seismic data from unconsolidated sediments containing gas hydrate and free gas. Geophysics, 2004, 69(1): 164-179.
Li C,Yin X Y, Zhang G Z, et al. AVO approximation elastic impedance equation and inversion based on incidence angle. Journal of Jilin University (Edition of Earth Science), 2013, 43(5): 1663-1671. (in Chinese)
Chen T S, Liu Y, Wei X C. Study on method of PP and PS waves joint AVO inversion. Journal of China University of Petroleum (Edition of Natural Science), 2006, 30(1): 33-37. (in Chinese)
Su Y, Cai Q X, Qin G S, et al. Discussion on selection of the k value in the elastic impedance equation. GPP, 2011, 50(4): 350-354. (in Chinese)
Veire H H, Landrø M. Simultaneous inversion of PP and PS seismic data. Geophysics, 2006, 71(3): R1-R10.
Du Q Z, Yan H Z. PP and PS joint AVO inversion and fluid prediction. Journal of Applied Geophysics, 2013, 90(3): 110-118.
Aki K, Richards P G. Quantitative Seismology: Theory and Methods. University Science Books, US(2nd edition), 1997.
Mahmoudian F. Linear AVO inversion of multi-component surface seismic and VSP data. University of Calgary, 2006.
Duffaut K, Alsos T, Rognø H, et al. Shear-wave elastic impedance. The Leading Edge, 2000, 19(11): 1222-1229.