Analysis of Carbonate Reservoir Characteristics and Main Controlling Factors of Iranian Azadegan Oil Field

Abstract

The carbonate reservoir space types and heterogeneity features, which influence the development of oil field, are comprehensively analyzed, taking carbonate reservoir in Sarvak Formation of Iranian Azadegan oil field as a case study. The rock types of Sarvak Formation are mainly composed of bioclastic grainstone, and the secondary dissolution porosity dominates the reservoir space, with reservoir permeability greatly improved by fractures. The relationship between porosity and permeability, dynamic production tests, and the MDT tests demonstrate that the vertical interbed heterogeneity and planar heterogeneity apparently exist in the carbonate reservoir of Sarvak Formation. The migration of high energy banks that developed on the gentle slope platform margin during Cretaceous Period formed the major part of favorable reservoir of Sarvak Formation. The development of carbonate reservoir is controlled by many factors, such as high frequency sea level change cycles, epidiagenesis that happened along the sequence boundaries, the faults and fracture developmental zones caused by later tectonic activities, as well as the hydrothermal dissolution that occurred along the faults. Sar-3 member and Sar-8 member are corresponded to the top parts of shallower upward cycle of third-order sequences, developing high energy grain banks. Concurrently, their locations near the sequence boundaries are easily exposed and dissoluble, with most developed reservoirs.