Open Journal of Geology, 2016, 6, 399-409 Published Online June 2016 in SciRes. http://www.scirp.org/journal/ojg http://dx.doi.org/10.4236/ojg.2016.66035 How to cite this paper: Irajian, A.-A., Bazargani-Guilani, K., Mahari, R. and Solgi, A. (2016) Porosity and Rock-Typing in Hy- drocarbon Reservoirs Case Study in Upper Member of Dalan Formation in Kish Gas Field, South of Zagros, Iran. Open Jour- nal of Geology, 6, 399-409. http://dx.doi.org/10.4236/ojg.2016.66035 Porosity and Rock-Typing in Hydrocarbon Reservoirs Case Study in Upper Member of Dalan Formation in Kish Gas Field, South of Zagros, Iran Ali-Akbar Irajian 1 , Kamaladdin Bazargani-Guilani 2* , Rahim Mahari 3 , Ali Solgi 1 1 Department of Geology, College of Science, Science and Research Branch, Islamic Azad University, Tehran, Iran 2 School of geology, University College of Science, University of Tehran, Tehran, Iran 3 Department of Geology, Faculty of Science, Tabriz Branch, Islamic Azad University, Tabriz, Iran Received 17 May 2016; accepted 21 June 2016; published 24 June 2016 Copyright © 2016 by authors and Scientific Research Publishing Inc. This work is licensed under the Creative Commons Attribution International License (CC BY). http://creativecommons.org/licenses/by/4.0/ Abstract To estimate the volume of oil and gas in the hydrocarbon reservoirs, the rock-typing must be con- sidered. The volume and type of available space in the reservoir rocks (porosity) and the ease of hydrocarbons flow (permeability) are important in the classification of rock-types. In the field study, touching-vug Porosities (intergranular, intercrystalline and brecciate) increase the total porosity and form high quality rock-types, on the other side, separated-vug porosities (such as moldic, intraparticle and vuggy) increase the total porosity but do not play a large role in the pro- duction of hydrocarbon. In this paper, based on the SCAL data (Special Core Analysis) and accord- ing to amount of irreducible water saturation (Swir) and capillary pressure, the reservoir rocks are divided into 4 classes including Reservoir Rock-Types 1 to Reservoir Rock-Types 4 (RRTs-1 to RRTs-4). By study of the prepared thin sections, we investigated the role of porosity in the rock-typing. Among the rock-types, category 1 is the best type-reservoir and category 4 is non-re- servoir. Probably, the latest diagenetic process determines the quality rocks, not sedimentary en- vironments. Keywords Porosity, Rock-Typing, Hydrocarbon Reservoirs, Dalan Formation, Zagros * Corresponding author.