Total organic carbon (TOC) contents and distribution within Upper Qamchuqa gas condensate reservoir—Kurdistan Region of Iraq

Barham S. Mahmood , Farhad A Khoshnaw, Mardin Abdalqadir, Sina Rezaei Gomari

Research output: Contribution to journalArticlepeer-review


Understanding the origin and distribution of oil/bitumen in reservoirs is crucial for minimizing uncertainty in reservoir volumetric predictions where TOC content affects effective porosity. The initial gas in place volume will be lowered as a result of the reduced porosity generated by TOC porosity filling. In this study, data from three wells with good areal coverage of the Khurmala oilfield were used to investigate the oil/bitumen distribution within the Upper Qamchuqa gas-condensate reservoir: well K-306 and K-436 in the north and well K-441 in the south of the field. Oil and bitumen presence are quantified in the reservoir as TOC content. The results showed that the oil/bitumen distribution in the gas zone is controlled by porosity/permeability and possibly fracturing; however, the relationship is not straightforward. Existing data highlight the variability of TOC content within the pore volume and, therefore, the associated high uncertainty of the pore volume occupied by oil/bitumen in the gas zone. Based on the Litho Scanner log data, it appears that the TOC volume in porosity decreases upwards in the reservoir. This could be related to either the decrease of hydrocarbon density and/or the decrease of oil and bitumen concentration towards the top of the reservoir in the well. The findings also revealed that TOC variations within the Upper Qamchuqa reservoir’s pore volume were significant. TOC occupies 3 to 28% of the pore space in well K-436. These values are significantly higher in well K-441, ranging from 31 to 50%. As a result, the volumetric impact of TOC filling the pore space in the reservoir is significant and must be taken into consideration when estimating hydrocarbon in-place volumes.
Original languageEnglish
Article number689
JournalArabian Journal of Geosciences
Issue number8
Publication statusPublished - 4 Apr 2022


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