Reservoir characterizations of the upper cretaceous deep marine turbidites to the close southern part of Sulaimaniyah (Northern Iraq)

In this study reservoir characterization of the low density turbidite sandstones of Upper Cretaceous Tanjero Formation cropping out next to the Arbat town in the southeastern part of Sulaimaniyah city, Northern Iraq was analyzed. The sandstone portion of the unit has been examined by measuring six sections through field and laboratory based studies which their thicknesses are about 40-50 meter, and taking samples from the outcrop. The sections are located on the southern limb of an anticline in the high folded zone which is characterized by intense folding and orogenic uplift with closely packed narrow anticlines and synclines. The outcrops of the formation are characterized by a sequence of sandstones, siltstones and shale. The base of the logs are not clear to see which formation is underlying the logs as they were taken from an outcrop that was brought surface by a small river next to the Arbat road and on an anticline limb. Possibly it was Shranish Formation which is generally comformably underlying the unit around the city. The analysis of lithofacies and architectural elements of the sandstones in the studied area, leads to recognition of three main lithofacies and forty-nine total subfacies of the turbidites in the location. The main facies represent the grain size from fine to coarse grain sandstone. The subfacies are consisting of many types of combinations of the complete Bouma sequence associated with turbidites. These facies point out that the environment of the turbidites is in the transition area between middle fan and outer fan. In the meaning of lobe hierarchy, the turbidite beds in thin and medium thicknesses represent lobe fringe. Only one architectural element recognized in the section is small sandy channel fills in about ten meters length and a few meters thick representing beginning of outer fan or in lobe fringe. For porosity and permeability tests 35 rock samples were taken from the logs for laboratory analyses. Porosity of the studied sandstones range from 4.56% to 16.56% which is poor to III beginning of fair with an average value of 9.2%. The obtained permeability varies between 36.388-623.328 md and their mean value is 426.68 md representing very good permeability. Petrographic works based on modal analysis of the clastic rock fragments and the other components such as cement, opaque minerals ect. show that these turbidites are mainly composed of sedimentary rock fragments such as carbonate, microcrystalline and cryptocrystalline quartz bearing siliceous sedimentary cherts, radiolaria fossil bearing cherts, and released radiolaria from the cherts during a short distance transportation. Quartz and feldspar ratios in the whole thin sections are below two percent. The modal analysis of the sandstones shows calclithite (litharenite) indicating sedimentary source rocks mainly consisting of carbonate rocks and radiolarian and chert rich limestone. The composition of the sandstones suggests a recycled sedimentary sources. Likewise, the Qm,F,L ternary diagram suggests that the sediments are derived lithic recycled provenance which may be the Lower Cretaceous Qulqula Formation. Keywords: Tanjero Formation, turbidite sandstone, reservoir characterization, Arbat southeastern Sulaimaniyah, Northern Iraq.