Detailed Seal Analysis, Lower Cretaceous Rocks of the North Sinai Basin, Egypt: Effects on Hydrocarbon Migration and Accumulation in Overpressured Regimes

NASHAAT, M., Egyptian General Petroleum Corporation, Cairo, Egypt

The filling mechanism of petroleum traps in the North Sinai basin has been studied, taking into account the area's maturation history, the hydrodynamic parameters, and the seal efficiencies. The purpose of this study was to ascertain whether or not sizeable accumulations of hydrocarbons could be expected and to investigate the origin of the oil discovered to date.

Formation pressure regimes in the North Sinai basin include highly overpressured reservoirs with undercompacted shale, starting at relatively shallow depths. The occurrence of overpressure is proposed to be dynamically induced by the very high subsidence rate during Upper Cretaceous/Eocene and Miocene to Recent. The high heat flow regime during the Syrian arc thrusting event (Upper Cretaceous/Eocene time) could have also contributed to the creation of overpressure.

In particular, the deeper closed hydraulic systems usually exhibit abnormally pressured regimes in individual fluid compartments. The pressure regimes are separated from each other by seals that are of particular interest to explorationists, as they frequently support oil and gas pools.

The fracture pressures as well as the formation pore pressures were used together in some wells to evaluate seal quality. This detailed seal analysis has identified many regional seals and pressure compartments and their lateral and areal extent. These seals seem to control the hydrodynamic regime in the underlying permeable Lower Cretaceous reservoirs, and along with source maturation strongly affect the migration of hydrocarbons from source rocks and their accumulation in reservoirs.

The water chemistry of the undercompacted sediments and overpressured reservoirs agrees with the different hydrodynamic systems mapped. Water chemistry zones clearly define different hydraulic systems. Originally, they are the freshwater aquifer of Lower Cretaceous overlain by higher salinity formations.

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)