Regional Pressure Study in the Deep Nile Delta
Mark W Alberty1, John Dolson2, Javed Ismail3, Sherif Montasser3, James Keggin3
(1) BP Exploration, Middlesex, United Kingdom (2) BP Exploration, Cairo, Egypt (3) BP-Egypt, Cairo, Egypt
Pressure is a key factor in understanding migration, trapping, reservoir fairways, drilling risks and costs. Pressure data from 80 regionally spaced wells and several basin model lines provides insight on regional Nile Delta pressure trends. A regional velocity pressure cube created from seismic interval velocity data shows a strong correlation with depositional facies, depositional rates and structure. Identification of “pressure regressions”, where reservoir pressures are significantly lower than those of the encasing shales, are readily apparent.
Compaction disequilibrium exerts the dominant control on pressure trends in Pliocene strata, with a secondary overprint by facies. The diagenetic conversion of smectite to illite dominated shales with temperature is an important secondary factor in the Lower Pliocene and pre-Miocene.
Pressure regressions to near hydrostatic in Messinian age strata result primarily from pressure release through laterally extensive valley-fill and alluvial plan sandstones that outcrop southward. In shale filled valleys or barren interfluves, high pressure dominates. Pre-Messinian strata show full regressions in delta plain sandstones subcropping the Messinian unconformity. Partial regressions occur in many deep-water slope-channel fairways. Regressions are largely absent in delta slope facies or other condensed intervals, where “hard pressure” is encountered.
The integrated approach used suggests that regional pressure trends may be predictable to depths of up to 4000 meters below mudline. This provides a powerful predictive tool for understanding plays, prospects and drilling hazards.