Abstract: The Middle-Upper Cretaceous carbonate reservoirs are the main pay zones in Halfaya oilfield of Iraq.Comprehensive analyses of cores,thin sections,physical property test results,mercury injection data and scanning electron microscopy (SEM) images were carried out on samples from typical coring wells in the reservoirs of the field to figure out rock types and characteristics in them.The results show that the mineralogy of the rocks is dominated by calcite and clay,with small amount of dolomite scattered locally.Components and their relatively contents in rocks vary greatly.Based on rock component types and characteristics,we constructed a three end-member framework with micritic matrix,foraminifera skeleton and bioclast/calcarenite limestone as each end-member,respectively,and proposed a classification scheme for rock types in the field.According to the scheme,the rocks can be categorized into three major classes (micrite,foraminifer limestone and bioclastic limestone/calcarenite) and nine sub-classes based on the contents of certain grains in the rocks.Different types of the rocks are observed to have various pore structure and physical characteristics-footprints of different sedimentary settings.Horizontally,the distribution of different types of rocks shows clear evidence of being controlled by sedimentary settings.And vertically,foraminifera limestone of greater thickness seems to be concentrating more on the Upper Cretaceous carbonate reservoirs.Bioclastic limestone/calcarenite was rather confined within certain areas and the Middle Cretaceous carbonate reservoirs contained mostly bioclastic limestone/calcarenite.Micrite is seen interbedded as thin layers in bioclast/calcarenite.And foraminifera limestone is rare.

Key words: rock type, carbonate, Middle-Upper Cretaceous, Halfaya oilfield, Iraq