Sedimentology and reservoir characterization of the Upper Miocene Qawasim Formation, El-Tamad Oil Field onshore Nile Delta, Egypt

摘要

The Upper Miocene Qawasim Formation is an important hydrocarbon reservoir in the Nile Delta Province. This paper presents the diagenetic features and the reservoir characteristics of this formation based on conventional core analysis performed on the El-Tamad-2 well. The Qawasim Formation is consisted of low compacted, poorly cemented, massive, and laminated sandstones with gradual upward facies change to tightly cemented bioclastic and dolomitic sandstones. The sandstones are capped by shallow marine bioclastic limestones followed by the open marine Globigerina wackestone and mudstone facies of the Pliocene Kafr El-Sheikh Formation. The channel-fill massive and laminated sandstones are classified as subarkose arenites with well-preserved primary intergranular porosity and good secondary porosity due to the dissolution of feldspars. In addition, they have low clay volume, well-connected pore spaces, and hence very good reservoir quality. On the other hand, the bioclastic and dolomitic sandstones were affected by the diagenetic alterations. Dolomite cement blocked the intergranular pores and reduced the primary porosity, while the dissolution of bioclasts and feldspars increased the secondary porosity. The reservoir quality decreases dramatically with increasing the marine influence from the channel-fill sandstones to dolomitic and bioclastic sandstones, shallow marine bioclastic limestone, and marine mudstone facies. The massive sandstones at the bottom of the upper part of the Qawasim Formation represent the best reservoir quality interval with excellent porosity and permeability values and have proven to be the main target for future exploration activities.