Messinian Seismic Stratigraphy of the Nile Delta: Identification of the RST (Regressive Systems Tract)
Abdel-Fattah, Mohamed; Pigott, John D.
The Messinian of the Nile Delta (Egypt) has become a major focus for gas exploration and production, but its exploration suffers from a complexity of stratigraphic relations within two major Messinian formations: the Early Messinian Qawasim and the Late Messinian Abu Madi formations. We have identified a new component for optimizing future exploration in the fluvial systems.
Seismic stratigraphic analysis of these two formations reveals the dynamic interplay between global and Mediterranean sea level oscillations. The observation of intradelta fluvial channel terraces on the delta during downstepping relative sea level falls reveal correlatable RST (Regressive Systems Tract) terraces of Pigott et al. (2011) incised by LST (Lowstand Systems Tract) channels and subsequent flooding by TST (Transgressive Systems Tract) delta incised backstepping channel fills culminating in HST (High Systems Tract) deposition.
Recognition of these RST sand geometries can aid in reducing exploration risk and assist in the development of strategies to identify similar high sand quality reservoirs in the Nile Delta distributary channels. The 2-D seismic observations reveal early Qawasim deposition and sedimentation are in response to global sea level changes but as the Mediterranean Sea closes, the Abu Madi responses are antithetic to global sea level changes. Specifically, the RST channels of the Qawasim Formation are represented by fluvial terraces of lateral accretion units in response to downward stepping base levels owing to a slowly falling global sea level base and shale channel fill during a global sea level rise. Good vertical sand reservoir quality but laterally disconnected geometries occur. The RST channels of the Abu Madi Formation are represented by incised valley fluvial channels which eroded most of Qawasim Formation deposits especially in the northward of Nile Delta in response to rapidly falling local sea level as the Mediterranean Sea became restricted and then are capped by a rapid transgression when the Mediterranean Sea suddenly reopened. Both Qawasim and Abu Madi fluvial RST and LST's exhibit good reservoir sand quality and charging potential, and moreover, are confirmed by identified gas wells as major hydrocarbon producers.
The identification of the fluvial RST stages can assist in the exploration of Messinian reservoirs of the Nile Delta and potentially to other coastal plain fluvial reservoirs elsewhere in the world.
AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013