Microfacies analysis and sedimentary environment of the Sarvak Formation in one of the oil fields in SW Iran

Introdaction Generally, sedimentary facies is a primary factor controlling framework and geometry of pores in reservoir rocks. However, in carbonate reservoirs, many of primary properties are changed due to the effect of diagenesis (Mazzullo 1994; Lucia, 2007; Ahr, 2008; Moore and Wade 2013). Microfacies and sedimentary environment of the Sarvak Formation have been vastly studied in different parts of the Zagros and Persian Gulf (Taghavi et al. 2006; Razin et al., 2010; Ghabeishavi et al. 2010; Mehmandosti et al. 2013; RahimpourBonab et al. 2012;). Nevertheless, there is less information about facies architecture and paleo-environment of the formation in the Abadan Plain, as one of the important exploration regions of SW Iran. The main parts of this paper is related to Facies description and depositional environment interpretation of the Sarvak Formation in two key wells of one of the giant oil field in the Abadan Plain region.

Materials and Methods The data used in this study includes a collection of information derived from cores and thin sections belonging to two key wells of one of the giant oil field in the Abadan Plain (430 m core and 1116 thin sections). The results from core description and thin section study were used for facies analysis. In this regard, some sedimentary properties such as lithology, texture, sedimentary structure and types of skeletal and non-skeletal grains were taken into account. Also, to reach a better understanding of sedimentary characteristics in thin sections, all of them were scanned using a CREO-IQSMART3 scanner at the Research Institute of Petroleum Industry (RIPI). The apparatus is a powerful scanner, which can be used for achieving high resolution images up to 10000 DPI.

Result and discussion Based on the results from the core descriptions and petrographic studies, the sedimentary texture, grain size, type and frequency of allochems, fossil content and other sedimentary parameters for the Sarvak Formation in the key wells were identified. Then, using this information and comparison with previous studies (Razin et al., 2010; Hollis, 2011; Mehmandosti et al., 2013; Rahimpour-Bonab et al., 2012, 2013) and standard models (Wilson 1975; Flugel 2010), 15 facies were recognized. The defined facies are representative of five facies belts including distal open marine, proximal open marine, slope, rudist biostrome-shoal and lagoon. The lagoon facies belt based on diversity of components and texture can be subdivided into open and restricted lagoon. On the basis of such evidences as facies association, rudist distribution as well as tectonic setting a shelf carbonate platform for deposition of reservoir part of the Sarvak Formation in an oil field in the Abadan plain (equivalent of Mishrif Formation in Mesopotamian Basin) has been proposed. With regard to reservoir potential of the area, the findings from facies analysis is thought to be valuable for better reservoir characterization and development