Rock-Eval analysis of source rock parameters in the Aryskum depression of the South Turgay Basin, Kazakhstan

The study is aimed at identifying potential oil and gas source strata at the Upper–Middle Jurassic clay deposits based on Rock-Eval pyrolysis data on samples taken at the East and Central Akshabulak deposits (Aryskum depression, South Turgay Basin, Kazakhstan). The data on the total organic carbon content (TOC), residual generation potential of organic matter (S2) on the pyrogram, productivity index (PI), oxygen and hydrogen indicators (HI & OI) and maximum pyrolysis temperature (Tmax) are summarized. However, only the East Akshabulak samples were used to assess hydrocarbon potential as the TOC of the Central Akshabulak rocks was less than 0.3%. The analysis results of the East Akshabulak rocks show that the S2 parameter of generation potential varied from satisfactory (0.58 and 2.48 mg HC/g) to very good (3.84 mg HC/g). In addition, it was found that the concentration of TOC 0.78 has a satisfactory generation potential, and the samples taken at the depths of 1960.9 and 1967.65 m have a very good oil and gas generation potential. The type of organic matter was also evaluated using the HI and the Tmax, which allowed concluding that the test samples contained type III kerogen, characterized by the release of mostly gaseous hydrocarbons. The thermal maturity of organic matter was also determined based on the values of Tmax and PI: by PI the test rocks were classified as immature, however the temperature values of the samples taken at the depths of 1960.9 and 1965.98 m pointed at their early stage of maturity. The research was supported by the Science Committee of the Ministry of Science and Higher Education of the Republic of Kazakhstan, Grant Agreement No. AP13268843.