The Theoretical Research On Zoeppritz Elastic Impedance Forward And Inversion

Conventional acoustic impedance (AI) inversion is based on an assumption of a P wave striking subsurface interfaces at normal incidence. When the offset range in a CDP gather is small and the reservoir is deep, such assumption is approximately satisfied and the inversion produces reliable results. However, in the presence of amplitude variation with offset (AVO), and particularly at large offsets, reflection coefficients and polarities may differ significantly from those at normal incidence. In such cases, conventional seismic trace inversion needs to be modified by taking the AVO effects into consideration.Several approaches to incorporating AVO effects in seismic inversion were proposed. Connolly (1999) put forward the concept of Elastic Impedance (EI), Although useful and efficient for capturing the AVO effects, this method relies on an unrealistic assumption of an S- to P-wave velocity ratio staying constant throughout the depth column. In order to overcome this limitation, Ma (2003) proposed a generalized, or Reflection Impedance (RI) derived by integrating the reflectivity along a reflection ray path. The S- to P-wave velocity ratio needs no longer remain constant;however, the density is assumed to be functionally related to the 5-wave velocity. Both Elastic Impedance and Reflection Impedance are possible only when the number of independent parameters is reduced to two. Besides, Elastic Impedance and Reflection Impedance also rely on a weak velocity and density contrast across an interface. These assumptions are quite restrictive and their validity is difficult to ascertain. Subsequently, Ma and Igor (2005) put forward the concept of Zoeppritz Elastic Impedance which is based on Zoeppritz equation and so is exact and accurate.In order to use Elastic Impedance and Reflection Impedance more better in practice, this thesis does some works, including:1. On the condition of fluid substitutions of two-layer media and multi-layer media, by comparision of Zoeppritz Elastic Impedance with Elastic Impedance andReflection Impedance, The quality of identifying fluid by Elastic Impedance and Reflection Impedance is analyzed.2. By processing and inverting synthetic seismic data and then by comparision of Zoeppritz Elastic Impedance inversion result with Elastic Impedance inversion result and Reflection Impedance inversion result, the main facters that affact Elastic Impedance inversion result and Reflection Impedance inversion result are found.3. This thesis also discusses how noise affact seismic inversion by processing and inverting synthetic seismic data with various ratios of signal to noise.