115 J. Adv. Appl. Geol. Summer, 2019, No: 32 Hydrocarbon continuity investigation of Sarvak and Ilam reservoirs in Azadegan oilfield using integration of geochemical, geological and reservoir engineering data Bahram Alizadeh 1,2 , Mehrab Rashidi 1,3 , Alireza Zarasvandi 1,2 , Seyed Rasoul Seyedali 1,2 , Mohammad Hasan Aliee 4 1- Department of Geology, Faculty of Earth Sciences, Shahid Chamran University of Ahvaz (SCU), Ahvaz, Iran 2- Petroleum Geology and Geochemistry Research Center (PGGRC), SCU, Ahvaz, Iran 3-Geochemistry Department, Exploration Directorate, National Iranian Oil Company (NIOC), Tehran, Iran 4-Geophysics Department, Exploration Directorate, National Iranian Oil Company (NIOC), Tehran, Iran Keywords: Reservoir geochemistry, Reservoir connectivity, Cretaceous reservoirs, Abadan Plain, Azadegan oilfield 1-Introduction The N-S trending Azadegan oilfield has been located in Abadan Plain, SW Iran, near the Iraq border. It considered being one of the largest undeveloped oilfields in the world. The Upper Cretaceous Sarvak (Turonian) and Ilam (Santonian) reservoirs, dominated by carbonate lithology, contain heavy oil and separated from each other by Shaly Lafan (Coniacian) Formation (Alizadeh et al., 2012, 2016; Du et al., 2016; Abdollahie Fard et al., 2006). The vertical continuity of Calcareous Sarvak and Ilam formations in Azadegan oilfield is unidentified. Therefore, in this study, organic geochemical methods were first used to specify geochemical and genetic characteristics of the Sarvak and Ilam reservoir oils. Subsequently, vertical continuity of these reservoirs was investigated using the integration of the results obtained from reservoir geochemical methods (England, 2007) with lithological information and reservoir pressure data. 2-Methodology A variety of geochemical analyses including liquid chromatography (LC), gas chromatography (GC), gas chromatography-mass spectrometry (GC-MS) and 13C stable isotope analysis were carried out on the Sarvak and Ilam reservoir oils. Also, C7 light hydrocarbon analysis was done to investigate the reservoirs continuity by detecting the compounds in the range of C5 to C9 using GC8000 instrument equipped with a flame ionization detector (FID). Measuring nickel (Ni) and vanadium (V) elements in the oil samples were performed using inductively coupled plasma-mass spectrometry (ICP-MS). Also, geological and lithological information of the studied reservoirs were extracted from the available reports and interpretation of the well logs, while the reservoir pressure data obtained from pressure measurements in the well test operation. 3-Results and discussion The data obtained from liquid chromatography analysis shows that a significant portion of the studied samples contains polar (resins/asphaltenes) and aromatic compounds. The gas chromatograph patterns of the oil samples are identical. However, the higher degree of biodegradation for the Ilam reservoir oil sample can be inferred from a larger unresolved hump in its chromatogram (Peters et al., 2005; Volkman et al., 1986; Connan, 1984). Tissot and Welte’s (1984) ternary diagram, which is constructed based on the amounts of saturated, aromatic and polar compounds, introduces the studied samples as paraffinic- naphthenic oils. The relationship between pristane/n-C17 and phytane/n-C18 ratios as well as the low values of terrigenous to aquatic ratio (TAR) and pristine/phytane < 1 (Table 1) all indicate a marine carbonate source rock for the oil samples, deposited in an actively reducing environment (Peters et al., 2005).  Alizadeh@scu.ac.ir