Prospect evaluation based on integrated petroleum system analysis: Block E case study, south-eastern edge of Precaspian Basin (Kazakhstan)

Abstract

Generative potential and thermal maturity for Upper Palaeozoic source rocks from the south-eastern edge of Precaspian Basin were determined using Rock–Eval. A high hydrocarbon source rock generative potential and high degree of thermal maturity for the Lower Permian, Mid-Carboniferous strata have been revealed based on 39 rock samples. TOC values of 0.4–5.5% have been obtained for mature source rocks. Integrated geochemical analysis determined from Rock–Eval studies combined with 1D basin modelling was utilized in order to reconstruct thermal evolution for the Upper Palaeozoic source rocks. Calibrated 1D models for three wells had been constructed to understand petroleum system. For two deep exploration wells (Nur-1 and Tassym SE-1), which penetrated pre-salt strata at the depths of 5.7 and 7 km, respectively, the impact of salt diapirism on timing of maturation was modelled. Type II kerogen was used, which is based on previous palaeogeographic studies. The stratigraphic framework and major stages of geodynamic evolution were analysed. Salt-related structural traps in post-salt strata have been described based on 3D seismic data, and additional intra-salt sediment packages have been delineated. Discovered producing oil fields in the Upper Triassic and Jurassic–Cretaceous stratigraphic sections are mainly confined to the four-way dip structural closures above the steep flanks of salt structures. Based on burial and thermal modelling, the maturation and generation behaviour of kerogen Type II below salt-related minibasins and close to thick salt diapirs were inferred. For Lower Permian SR with type II kerogen, the generation peak (maturity over 50%) occurs in Middle to Late Jurassic. For predominantly carbonate and terrigenous-carbonate Mid-Carboniferous marine SR, generation peak occurs earlier below salt withdrawal minibasins. Implications for deeper hydrocarbon prospectivity were made for the study area, and methodology for evaluating hydrocarbon potential adopting 1D basin modelling technique and geochemical data is presented.