Source rock potential and reservoir characterization of the Lower Cretaceous Sarmord Formation in selected sections in Kurdistan Region-Iraq

Abstract

The Sarmord Formation is underlain by the most important source rocks and overlain by several major reservoirs in the Kurdistan Region. Two sections including a subsurface (well from Kirkuk oilfield) and a surface (outcrop at Bekhme Gorge) of the Sarmord Formation were studied to identify and describe the role of the Sarmord Formation within petroleum systems in the region. Thus, organic geochemistry and petrophysical characteristics of the Sarmord Formation have been studied using Rock-Eval, log data, core analysis and thin section studies. Results showed different lithologies between the studied sections of the Sarmord Formation; an intercalating of yellowish-gray marl (calcareous mudstone) and dark brownish to dark-gray shale was observed at outcrop, and subsurface section was mostly composed of clays with a composition of limestone and dolomite. The source rock potential of the shale layers of the Sarmord Formation reveals that the total organic carbon (TOC wt%) of subsurface section is 0.22 wt% on average which is regarded as poor organic carbon content. The average of Tmax value is 426 °C that shows the formation is thermally immature. The capability of formation in generating of hydrocarbons is poor at subsurface section. Whereas the surface (outcrop) samples show fair to good content of organic carbon (0.83 TOC wt% on average), and they are thermally mature (Tmax is 440 °C on average). The hydrocarbon generative potential of outcrop seems to be poor to good. The petrophysical study of the subsurface section displays low porosity and permeability (0.04% and 0.04 mD on average respectively). These values are generally considered as poor reservoir quality. Likewise, measurement values of porosity and permeability from outcrop are 6.425% and 0.108 mD on average, respectively, showing poor reservoir quality. The microscopic study also shows that the matrix material is largely comprised of lime mud and allomicrite types, and its porosity types (particularly of vague and fracture types) indicate the low percentage of porosity (not exceeding 1%). On the other hand, presence of bitumen seeps along fractures at the outcrop section may reveal that the formation can be regarded as a fractured-reservoir.