SEQUENCE STRATIGRAPHY AND HYDROCARBON POTENTIALITIES OF THE NEOGENE-QUATERNARY OFFSHORE SUBSURFACE SEDIMENTS, NORTHWEST OF SINAI, EGYPT

Abstract

The study area lies 50 km in the offshore part of the Mediterranean sea, northwest of Sinai between latitudes 31o 201 and 31o 581 N and longitudes 32° and 32° 50' E. The subsurface data of the study include 34 seismic reflection profiles and data of about 15 wells penetrated the study area. The Neogene-Quaternary offshore sediments northwest of Sinai are composed of five rock units namely from base to top; Wakar (Upper Miocene), Rosetta (Messinian), Kafr EI-Sheikh (Pliocene), Wastani (Upper Pliocene) and Mit-Ghamr (Plio- Pleistocene) formations. The constructed seismic velocity maps for the examined rock units indicated that the increasing in average velocity value with depth is clearly detected. On the other hand, the interval velocity graphs demonstrated the vertical variations between the examined rock units as a result of the lithofl:)gical differences between these rock units. The detailed investigations carried out on the seismic reflection profiles have shown that the Neogene-Quaternary subsurface succession of the study area is essentially affected by different types of faults {normal, strike-slip and growth faults) and shale diapers. Some other structural features are present associated to the present faults, including; tilted strata, rollover anticlines, synthetic and antithetic structures. The structural time contour maps of the studied succession reflect the dominance of three fault trends; the WNW-ESE, the ENE-WSW and the E-W trends. Detailed analyses of the examined data have enabled to determine six seismic facies forming the whole succession representing the progressive cyclic evolution of the examined succession. Two seismic facies (MSF-1 and MSF-2) are found constituting the Upper Miocene sediments related to a marked fall in the Mediterranean Sea level whereas the Pliocene rocks are represented by three seismic facies (PSF-1, PSF-2 and PSF-3) n lated to one complete sea level cycle. The Pleistocene sediments are represented by one laterally continuous seismic facies (GSF) related to the eastward progradation of the Nile Delta into the study area. Detailed sequenr.e stratigraphic analysis has revealed five third-order major depositional sequences bounded by four sequence boundaries (Sb1, Sb2, Sb3 and Sb4). The Late Miocene sequences include two sequences, MSq-1 and MSq-2 whereas the Plio-Pleistocene sediments are represented by the sequences, PSq-1, PSq-2 and P-QSq. The different characteristics of each sequence are discussed in detail including their boundaries, transgressive and maximum flooding surfaces and the seismic features of the enclosing systems tracts. The evolution of the encountered sequences has revealed cyclic fluctuations mainly related to the sea level oscillations of the paleo­ Tethys during the Neogene-Quaternary times. Moreover, the study provides some helpful recommendations for further hydrocarbon prospects in the Egyptian offshore: 1) The exploration should be directed to the stratigraphic traps comprising the sandy levels within the high-stand system tracts (1st priority) and the sand levels within the transgressive systems tracts (2"d priority). 2) The exploration should be directed to the combination traps consisting of the sediments of Pliocene sequence-2 (PSq-2) when only affected by the rollover anticlinal folds.