Research paperFault block rotation and footwall erosion in the southern Suez rift: Implications for hydrocarbon exploration

- Five major fault blocks dipping 30-40°SW exist in the southern Gulf of Suez rift.
- The major faults in the area include rift initiation, early syn-rift, and main syn-rift faults.
- The rift initiation faults played a major role in the erosion of pre-rift reservoirs and top seals.
- The lowermost syn-rift unit did not cover the eroded updip areas of the tilted fault blocks.

A dataset in the southern Suez rift including 400 km2 of 3D depth-migrated seismic data, thirty six boreholes with geological information and outcrop data from several exposures, was examined and interpreted in order to understand the controls on the erosion of the pre-rift reservoirs at the updip edges of tilted fault blocks and its impact on hydrocarbon exploration. Surface and subsurface mapping demonstrated the existence of five regional major tilted fault blocks bounded by major down to the northeast, rift-parallel normal faults. These blocks are characterized by steep stratal dip (30-40°) and their bounding faults are dipping at 20-30° toward the NE. The major faults in the area have been subdivided into three phases based on their age. The first-phase faults were formed at the early rift opening phase and were contemporaneous with the deposition of the lowermost syn-rift unit (Nukhul Formation). The second-phase faults are contemporaneous with deposition of the Rudeis Formation (main syn-rift unit) while the third-phase faults are the youngest. Detailed study indicates that the first-phase faults controlled the rotation of the tilted fault blocks and played a major role in the erosion of the pre-rift reservoirs and top seal units at the updip edges of these blocks. The lowermost syn-rift unit (Nukhul Formation) was deposited in the downdip areas of the tilted faults blocks and did not cover the updip eroded areas. A proposed model to demonstrate the risk of drilling the crests of tilted fault blocks close to the main block-bounding faults is described in this paper and can be applied in other highly extended rift basins.