Techniques for seismic delineation of complex structure: A case history

Abstract

Techniques for exploring in structurally complex areas were derived from recording and interpreting a single seismic line across the thrust‐faulted west flank of the Casper Arch. Line 306 was recorded to delineate a suspected subthrust prospect. The line was oriented along true dip based on the attitude of outcropping beds. We used short arrays and high‐fold stack, resulting in good data quality, especially in imaging of steep dips from the hanging wall. A two‐dimensional depth model of the structure was constructed. Outcrop dips constrained the interpretation and helped model the hangingwall. A correct model was confirmed when its synthetic time response (time model) matched the real reflections of a near‐offset section. Key to this match was accurate delineation of the hangingwall, which was confirmed when the model’s time response from the subthrust beds matched the static shifts of these same reflections on the real data. A perfect depth model was not achieved, however, due to constraints of the modeling program and the complexity of the thrust‐fault zone. Not all objectives of the project were met: no prospect was found, and proper migration of the data was never achieved. However, the field techniques used did provide good record quality, and the static problems were adequately handled. The final depth model was a reasonably accurate structural picture, although greater confirmation of its accuracy might have been achieved if a crossline had been available. In addition, the model might have been constructed more accurately and in less time using a real‐time, interactive modeling program.