Exploring the High Zagros (Iran): a challenge for geophysical integration

The purpose of a combined geological and geophysical study in the High Central Zagros area near the townships of Lordegan and Yasuj was to find answers to the following main questions: ■ Is the High Zagros Fault (HZF) an overthrust fault? ■ Are there vertically separated structural/ tectonic units in the ‘Complex’ Foreland of the Zagros? ■ Are there possible hydrocarbon exploration targets beyond the HZF? While Bosold et al.(2005) have published the results of a geological study, this paper focuses on the geophysical contribution to the above questions. Integration of seismic and potential field geophysical methods played a key role in this study. The area of investigation is located in the Zagros Fold-Belt (‘Complex’ Zagros Foreland), close to one of the oldest and richest oil and gas provinces in the world and the Zagros Thrust-Belt (High Zagros). Most of the oil and gas fields were discovered in the ‘Simple’ Zagros Fold-Belt in front of the Mountain Front Fault (MFF), which marks the front of the ‘Complex’ Zagros Foreland. Decades of successful activity of the petroleum industry have led to the acquisition of extensive knowledge of this area, whereas the orogenic zones further into the interior of the Zagros have been studied to a much lesser extent. The higher degree of structural complexity in combination with rugged surface topography is one of the main reasons. In the area between the Mountain Front Fault (MFF) and the High Zagros Fault (HZF) little seismic has been acquired previously and few wells have been drilled. These wells are often based exclusively on surface geology without seismic control, many of them having resulted in petroleum discoveries. North of the HZF, however, no data other than detailed surface geological mapping have ever been acquired prior to this study. In 2000, the exploration team of RWE Dea realized that new or previously undetected exploration plays could be present in the ‘Complex’ Zagros Foreland or even in the High Zagros adjacent to the established petroleum province. In 2001 a profirst posed two and a half year joint study programme in the Lordegan-Yasuj area was agreed with NIOC.