Preliminary Hydrocarbon Potential Evaluation of Hojedk Formation in Kerman Coaly Syncline (KCS), Iran: Geochemical Approach

To evaluate the hydrocarbon potential of coal seams (D and E horizons) and their country rocks of Hojedk Formation (Middle to Upper Jurassic) at Kerman Coaly Syncline (KCS), 32 coal and 46 shale samples were collected. These samples were studied geochemically, and their quantity, quality and thermal maturity of organic matter were studied as well. According to Rock-Eval pyrolysis data, it was found that the total organic carbon (TOC) content of coal samples is in excellent condition. Such a situation is, more or less, the same for the shales. Genetic potential (GP) also indicated that the majority of the samples have acceptable potential for gas and oil generation. Therefore, the organic matter quality of Hojedk Formation was evaluated as good to excellent generally. The use of hydrogen Index (HI) as one of the most important factors determining the quality of source rocks showed that the coal and shale samples of Hojedk formation have fewer than 50 to over 600 mgHC/g rock, and majority of the samples fall in 50-200 and 200-300 mgHC/g rock category and therefore, it can be stated that the quality of organic matter varies from without potential to gas and oil potential. The existing kerogen types in these samples are mainly of the III and II-III and consequently, gas and oil generation in the region is likely. Relative high values of S2/S3 (3.70 to 402.36) confirmed the above-mentioned products. In order to evaluate the thermal maturity of organic matter, two different methods (Tmax and vitrinite reflectance) were used. Tmax values revealed that most samples of KCS are in the early to late oil generation window conditions. The highest Tmax (overmature condition) is related to the Tikdar stratigraphic section and this is probably due to its proximity to the Kuhbanan fault. Measurements of vitrinite reflectance also showed that Ro% ranges from 0.5 to 2% and the mean value of this factor is 1.18% and therefore, corresponds to the condition of oil generation window. Finally, based on the quantity, quality and thermal maturity of organic matter at KCS, it can be said that the region has adequate potential for gas and to a minor extent oil generation. Moreover, coal seams, because of enough liptinite contents (up to 22%), are in a better condition in general.