The Effect of Ductile-Lithic Sand Grains, Overpressure and Secondary Dissolution on Porosity and Permeability and Their Relevance to Hydrocarbon Exploration in Aşkale Sub-Basin, East Anatolia, Turkey

Abstract

Ductile lithic grain, secondary porosity, temperature, and overpressure control porosity and permeability in the Mio-Pliocene and Upper Oligocene sandstones of the Aşkale sub-basin in East Anatolia. Ductile lithic grains account for between approximately 60–90% of the original sand grain population. There is a pronounced loss of porosity with increasing bruial depth in this sub-basin. At depths of less than 3000 m, this is due solely to ductile-lithic grain compaction where the rate of porosity loss of with depth increases with increasing ductile-lithic grain content. But at depths greater than 3000 m, the steep porosity increases with depth due to secondary solution activities and overpressure in the Aşkale sub-basin in East Anatolia. Secondary porosity is a common diagenetic feature in the more deeply buried (> 3000 m) sediments in the Aşkale sub-basin. The secondary porosity arises principally from dissolution of feldspar, to a lesser extent, of the quartz (approximately 10–30%). Overpressure is due to tectonic stress. Reservoir quality is thus controlled by secondary solution activities, overpressure, temperature (geothermal gradient) and depth of burial in the Aşkale sub-basin in East Anatolia Basin.