Linking Diagenesis to Sequence Stratigraphy – An Integrated Approach for Reservoir Characterization of the Coniacian-Santonian Mixed Siliciclastic-Carbonate Matulla Formation, West Central Sinai, Egypt

Abstract

The Coniacian-Santonian Matulla Formation contains both reservoir and source rocks in the Gulf of Suez region, the most prolific oil fields in Egypt. Outcrops of the Matulla Formation at west central Sinai (eastern side of the Gulf of Suez) provide a useful analog to these subsurface reservoirs by providing insight into facies distribution and stacking patterns, as well as porosity development and occlusion. The Matulla Formation was studied in four outcrops in west central Sinai, to determine facies associations, depositional environments, facies stacking patterns, diagenetic history and constrain a high resolution sequence stratigraphic framework. The study revealed that the Matulla Formation is composed of wave and tide influenced mixed siliciclastic-carbonate rocks interbedded with some oolitic ironstone beds. Detailed facies analysis suggests deposition in coastal and shallow marine environments. Vertical and lateral facies successions revealed that the Matulla Formation is composed of three 3rd order depositional sequences made of up higher frequency 4th and 5th order sequences and cycles. Primary facies and diagenetic modification both play key roles in the reservoir potential of the Matulla Formation. Sandstones are characterized by primary intergranular porosity with minor amounts of dissolution porosity, whereas carbonates exhibit dissolution molds, vugs, and some fractures. In both cases, porosity is best developed in particular facies and during preferred sequence stratigraphic positioning. Occlusion of porosity, especially in the carbonates, through both syndepositional marine cementation and extensive meteoric cementation is also linked to facies and sequence stratigratigraphic positioning. Preliminary investigations show that the porosity of sandstones increases in sequence 1 and sequence 2 and with some exceptions, sandstones with higher porosity in these sequences are associated with highstand systems tracts and exhibit some feldspar dissolution and kaolinitization of mica. Occlusion of primary porosity in many sandstone units resulted from the extensive cementation with poikilotopic calcite cement, although some of these units have secondary dissolution porosity.

AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015