Improvement of seismic structural interpretation of Zagros fold-thrust belt by dip scanning in common diffraction surface imaging method

Abstract

Geological interpretation and seismic imaging on data acquired from complex media, especially when accompanied by a thick layer of salt and/or anhydrate, is always a controversial task. The aim of this study is to introduce a method for seismic imaging of complex structures and study the folding scenario of the Zagros overthrust in SW Iran based on the improved seismic image processed by the proposed method. A diffraction based version of the common reflection surface stack method, called the common diffraction surface (CDS), was selected to enhance quality of seismic image from the Zagros fold-thrust belt. The 2D CDS method was also developed here to 3D partial CDS. Consequently, three sets of 2D and a set of 3D seismic data were processed with the conventional Kirchhoff prestack time migration and the partial common diffraction surface methods. Geological models released in previous studies of the Zagros overthrust were used as the base model of interpretation. Structural interpretation on seismic sections with new method was in accordance with previous geological models and improved in some parts where the new method could enhance quality of the seismic image. Seismic structural interpretation shows the inner part of the belt was subjected to folding, uplift and erosion. This mechanism constituted a resistant mass in the Dezful Embayment in front of the SW moving thrust and folds. This resistant mass formed tightly folded or thrusted and highly shortened structures in the Izeh zone and High Zagros area. In the oil rich zone of the Dezful Embayment, the thick evaporate—rich Gachsaran Formation, decouples the folding above it from the folding below, making seismic imaging of potential traps beneath the detachment horizons extremely difficult.