ABSTRACT
Organic rich sedimentary rocks of the Late Cretaceous Muwaqqar Formation from the Lajjun outcrop in the Lajjun Sub-basin, Western Central Jordan were geochemically analyzed. This study integrates kerogen microscopy of the isolated kerogen from 10 oil shale samples with a new finding from unconventional geochemical methods [i.e., ultimate elemental (CHNS), fourier transform infrared spectroscopy and pyrolysis-gas chromatography (Py-GC)] to decipher the molecular structure of the analyzed isolated kerogen fraction and evaluate the kerogen composition and characteristics. The optical kerogen microscopy shows that the isolated kerogen from the studied oil shales is originated from marine assemblages [i.e., algae, bituminite and fluorescence amorphous organic matter] with minor amounts of plant origin organic matter (i.e., spores). This finding suggests that the studied kerogen is hydrogen-rich kerogen, and has the potential to generate high paraffinic oil with low wax content. The dominance of such hydrogen-rich kerogen (mainly Type II) was confirmed from the multi-geochemical ratios, including high hydrogen/carbon atomic of more than 1.30 and high A-factor of more than 0.60. This claim agrees with the molecular structure of the kerogen derived from Py-GC results, which suggest that the studied kerogen is mainly Type II-S kerogen exhibiting the possibility of producing high sulphur oils during earlier stages of diagenesis, according to bulk kinetic modeling. The kinetic models of the isolated kerogen fraction suggest that the kerogen conversion, in coincidence with a vitrinite reflectance range of 0.55-0.60%, commenced at considerably lower temperature value ranges between 100 and 106 °C, which have produced oils during the early stage of oil generation. The kinetic models also suggest that the commercial amounts of oil can generate by kerogen conversion of up to 50% during the peak stage of oil window (0.71-0.83%) at relatively low geological temperature values in the range of 122-138 °C. Therefore, further development of the Muwaqqar oil shale successions is highly approved in the shallowly buried stratigraphic succession in the Lajjun Sub-basin, Western Central Jordan.
ABSTRACT
This investigation looks at the Late Triassic Baluti Formation's organic geochemical, mineralogical, and petrographical characteristics from a single exploration well (TT-22) near the Taq Taq oilfield in northern Iraq. The Baluti Formation shale samples that were studied in the studied well have high total organic carbon (TOC %) values up to 4.92 wt % and mostly hydrogen-rich types I and II kerogen with a minor gradient to types II/III and III kerogen, indicating a good oil-source rock. The hydrogen-rich kerogen was also confirmed by various organic matter (OM) origins and depositional environment-related biomarkers. The biomarker indicators demonstrate that the Baluti shale was deposited under anoxic conditions and contains a variety of OM generated mostly from algae marine and other aqueous organic materials, along with some terrigenous land plants. The geochemical and optical maturity indicators show that most of the examined Baluti shale samples, with a deep burial depth of more than 4000 m, are thermally mature, thus defining peak-mature to late-mature stages of the oil generation window. According to the basin models, from the late Miocene to the present, between 10 and 59% of the kerogen in the Baluti shale source rock has been transformed into oil, which is consistent with the VR values between 0.77 and 1.08%. The presence of the oil crossover in these shale rocks with an oil saturation index of more than 100 mg HC/g rock supports the maximal oil generation from the Baluti source rock system. Additionally, there was little oil expulsion from the Baluti source rock system at the end of the late Miocene, with transformation ratio values below 60% (59%). Considering the more significant oil generation and little expulsion, a high pressure was generated and forced the brittle minerals of the Baluti shales (mainly quartz), creating a natural fracture system as recognized and observed in the thin section. This natural fracture system enhances the porosity system of tight shale rocks of the Baluti Formation, giving rise to a high probability of oil production using hydraulic fracturing stimulation.