The Study Of P-wave Impedance Inversing Method In Depth Domain

Seismic inversion as the core technology of reservoir prediction, can combine the advantages of both the vertical resolution of log and lateral dense sampling of seismic. It can also estimate the variation of information which contains formation lithology and physical feature and has been widely used in various stages of exploration and development of oil and gas. Despite seismic inversion has achieved tremendous progress in recent years, current conventional method is performed in time domain. Because changing the logging data from depth domain into time domain has the loss of valuable information of high frequency, the limitation of seismic inversion in time domain is its poor ability to recognize the thin-bed. With the development of exploration, seismic inversion in time domain due to its own limitations is unable to meet the requirements of the fine reservoir description.The technology of pre-stack depth migration has a rapid development and gradually mature in recent years, therefore, it is a general trend to carry on seismic interpretation and reservoir inversion in depth domain. Inversion in depth domain is based on the seismic velocity field data which is got from pre-stack depth migration, and completes high-resolution inversion. This overcomes the loss of high-frequency which is generated from resampling, in the process of time-depth conversion, and ensure the high-resolution of inversion. It is significant to improve the success rate of lithologic reservoir exploration.On the basis of previous studies, this paper concretely realizes the method of inversion in depth domain. First, by studying the difference of wavelet in depth domain and time domain, a way which replaces the velocity to achieve convolution in depth domain is found. The main idea is to ensure the inter travel time is constant, transform the velocity and depth, to extract the medium velocity of seismic wavelet as standard velocity, and adjust the velocity of other layers to this standard velocity, interlayer thickness is also regularized. This is called pseudo-depth transform of seismic data. After conversion, wavelet and log in depth domain can achieve convolution, calibrate the mark of using log generated synthetic seismograms in depth domain. Then, by means of analysing and determining the parameters of inversion, the result of inversion in depth domain can be obtained.