Petrography and Petrophysical Characterization of the Precambriam Hydrocarbon-Bearing Reservoirs, Gulf of Suez, Egypt

By

Amr H. Elewa¹, Mohamed A. EL-Sharkawy², Mohamed Darwish²

(1) PETROBEL, Cairo, Egypt (2) Cairo University, Cairo, Egypt

 The present work deals with the geology and petrophysical characteristics of the Precambrian basement rocks and their hydrocarbon potentialities in the southern subprovince, Gulf of Suez. The available data are wireline logs, ditch cuttings and selected core samples of 13 wells; ten of which represent two oil fields: Ashrafi and Zeit Bay.

The petrography revealed coarse to medium crystalline granites with some exceptions in Abu Nigar-C-1 well where granodiorites are recorded. In Umm Agawish-1 well some diabase occurs across the granitic suits. Microfractures are found in two types: oriented sets along crystal contacts and cleavage planes and random sets crossing the crystals and framework. Secondary minerals filling these fractures are: carbonates, sulphides. iron oxides and sulphates. Some of these rock suites were differentially affected by alteration being manifested along cleavage planes and/or fractures. Three alteration stages could be deduced: the first during the Precambrian uplift and erosion phase; the second during the pre-Carboniferous uplift and erosion phase and the third was Pre-Miocene.

The integration between petrophysical and petrographical interpretation revealed the following main results: 1.The leaching of the alteration products of the feldspars in the granitic rocks led to the decrease of Gamma Ray and an increase of effective porosity. These also enhanced the calculated rock permeability. 2. Alteration along crystal margins is more effective for the reservoir performance. 3. The granitic suites being subjected to partial alteration under the effect of acidic water have a lower reservoir quality than those being affected by alkaline water.