Analysis of Subsurface Fractures in Cenomanian Carbonates in North Sinai, Egypt

M. Taha, S. El-Kawa, R. Nurmi

The geologic aspects of fractures in Cenomanian carbonates in an exploration well, Raad 1, in northern Sinai, Egypt, have been analyzed to determine their dip, strike, vertical distribution, and origin. This well is located southwest of the Sadot gas field along the same structural trend.

Two major fractures trends, N15°W and N85°W, in the Raad 1 well comprise a shear fracture system. These shear fractures are observed directly using borehole electrical imagery and are also identified using polar plots of fracture orientation. The relationship of these shear fractures to both the local structure, using seismic and dipmeter data, and regional structure, using Landsat imagery and regional geologic maps, suggests that these tectonic shear fractures were initiated by the same complex wrench faulting which formed the Syrian arc. The northwest-southeast bisector of the shear fracture system is parallel to the northwest compressive force which formed the Syrian arc.

Lithology and porosity are the dominant factors controlling fracture density in this well. Shaly zones are relatively fracture free, whereas low-porosity dolomitic zones have the highest density of fractures. Nearly all of the fractures analyzed are open and uncemented. Drilling-induced fractures were identified and excluded from the final fracture analysis. Surprisingly, the fractures are more abundant and closer spaced in more massive beds than in thin-bedded intervals.

AAPG Search and Discovery Article #91032©1988 Mediterranean Basins Conference and Exhibition, Nice, France, 25-28 September 1988.