Reservoir properties of Karaisalı formation in the Adana Basin, Southern Turkey

Abstract

This paper reports microfacies, diagenesis and reservoir properties of the Lower–Middle Miocene Karaisalı Formation in the Adana Basin, southern Turkey. The Karaisalı Formation reflects the continuous deposition of shallow-shelf carbonates; periodic rises in sea level led to episodes of deeper water sedimentation. The formation was studied using outcrop samples from the Karaisalı region. Karaisalı Formation carbonates are up to 500 m thick. Abundant bioclasts include corals, red algae, bryozoans and benthonic and planktonic foraminifera. The best reservoir conditions in the Karaisalı Formation occur in grain-supported facies such as Foraminiferal–Algal packstones. Secondary vuggy and moldic porosity, which are common in the Foraminiferal/Algal Packstones, resulted from micritic cement and the dissolution of skeletal grains during early diagenesis. Foraminiferal/Algal Packstones are characterised by porosities of > 20% and by permeabilities between 7 mD and 18 mD. Other carbonate facies, such as planktonic wackestones and coralgal boundstones have poorer reservoir characteristics. Most pore throats (50% or more) range between 1 and 2 µm, and only a small percentage of pore throats are less than 1 µ. These results indicate that the Karaisalı limestones have intermediate – good reservoir characteristics. The carbonates were affected by a range of diagenetic processes, including grain dissolution which led to the formation of secondary porosity reduced by calcite cementation. The wackestone and boundstone facies of the Karaisalı limestones are not suitable targets for hydrocarbon exploration in the Adana Basin. However, the Foraminiferal/Algal packestone facies may have a higher exploration success.