PRE STACK DEPTH MIGRATION ANISOTROPI UNTUK PENCITRAAN STRUKTUR BAWAH PERMUKAAN

Abstract

Anisotropic Pre Stack Depth Migration method has been carried out for 2D seismic reflection data on Line SP-2043. This method was chosen to construct geologic features and the subsurface structure. The aim of This research is applying an assumption of the anisotropic media by velocities variation vs angle in Pre Stack Depth Migration to get a better structure imaging. The simplest form of anisotropic media (VTI (Vertical Transverse Isotropy) was used. Theoretically, this form requires two parameters to describe the media, those are δ and ε. δ is an anisotropy parameter that describe velocity variation near to vertical while ε is an anisotropy parameter that describe velocity variation near to horizontal. Combination of δ and ε describes the non hyperbolic component of moveout and δ also controls the true depth. The anisotropic velocity interval is derived from transformation of isotropic velocity interval and δ anisotropic parameters. The anisotropic velocity is used for Pre Stack Depth Migration, and then refines on anisotropic interval velocity, ε interval. The process should be done until getting flattened event on every CRP (Common Reflection Point) gathers. In this research, the P wave anisotropy depth imaging is applied on real data set. The section resulted from anisotropic Pre Stack Depth Migration method shows a pattern of reflector to be more continuity rather than isotropic Pre Stack Depth Migration. The anisotropic Pre Stack Depth Migration produce a section which has clearer fault image and has change to be the true of reflector position. Base on well and seismic data calculation process, an anisotropic parameter is in the range of -0,1 – 0,09. Generally, Anisotropy Pre Stack Depth Migration method gave better result than isotropy Pre Stack Depth Migration.