Nonstationary seismic-well tying with time-varying wavelets

Seismic-well tying is an important technique for correlat-ing well-logging curves in depth with seismic traces in time. An appropriate seismic-well tying technique must account for two types of nonstationarity: the nonstationary time errors in the synthetic seismic trace caused by the inaccurate time-depth relationship established based on sonic-logging velocity and the nonstationary seismic signals due to the time-varying wavelets during wave propagation. The nonsta-tionary problems related to the time-depth relationship and the time-varying wavelets are interrelated in seismic-well ty-ing procedure. We implemented a nonstationary seismic-well tying method by iteratively updating the time-depth relation-ship and estimating the time-varying wavelets. From the esti-mated time-varying wavelets, we also estimated a Q -value by assuming that the subsurface medium has a constant Q at depth and used the constant Q to constrain the variation of the seismic wavelet during propagation. Then, we used the improved time-depth relationship and time-varying wavelets with the Q constraint for further iterations. In the iterative pro-cedure, we quantified the accuracy of the seismic-well tying result using the correlation coefficient between the synthetic and the true seismic trace in each iteration and evaluated the reliability using the normalized mean-square errors among the wavelets estimated in different iterations.