3D ray-trace modeling to assess the effects of overburden and acquisition geometry on illumination of pre-evaporite reservoirs in Karachaganak Field, Kazakhstan

Abstract

The specific goal of this study was to gain a clearer understanding of the effects of stratigraphically complicated overburden and acquisition geometry on amplitudes at and close to the Tops of pre-evaporite reservoir reflectors in Karachaganak Field in Kazakhstan (Figure 1). The 3D ray-trace modeling revealed significant irregularities in illumination coverage and considerable amplitude variations at the pre-evaporite reservoir levels. The results demonstrated that these illumination irregularities can be attributed to four discrete causes: thick salt bodies varying in lateral geometry and exhibiting complex boundaries; rapid lateral velocity changes within carbonate and evaporate bodies; steep dip; and rugged topography of reservoir interfaces. The combined effects of these factors resulted in severe raypath bending and distortions. These distortions not only lead to irregularities in the fold-of-coverage and reduced presalt reflection amplitudes but also tend to create traveltime anomalies and artifact...