Source rock characteristics and depositional environment of Lower Cretaceous Dsunbayan oil shales, Mongolia.

ABSTRACT Five oil samples reservoired in the Cretaceous Mishrif Formation from the Ratawi, Zubair, Rumaila North and Rumaila South fields have been analysed using Gas Chromatography – Mass Spectroscopy (GC-MS). In addition, fifteen core samples from the Mishrif Formation and 81 core samples from the Lower Cretaceous and Upper Jurassic have been subjected to source rock analysis and palynological and petrographic description. These observations have been integrated with electric wireline log response. The reservoirs of the Mishrif Formation show measured porosities up to 28% and the oils are interpreted as being sourced from: (1) Type II carbonate rocks interbedded with shales and deposited in a reducing marine environment with low salinity based on biomarkers and isotopic analysis; (2) Upper Jurassic to Lower Cretaceous age based on sterane ratios, analysis of isoprenoids and isotopes, and biomarkers, and (3) Thermally mature source rocks, based on the biomarker analysis. The geochemical analysis suggests that the Mishrif oils may have been sourced from the Upper Jurassic Najma or Sargelu formations or the Lower Cretaceous Sulaiy Formation. Visual kerogen assessment and source rock analysis show the Sulaiy Formation to be a good quality source rock with high total organic carbon (up to 8 wt% TOC) and rich in amorphogen. The Lower Cretaceous source rocks were deposited in a suboxic-anoxic basin and show good hydrogen indices. They are buried at depths in excess of 5,000 m and are likely to have charged Mishrif reservoirs during the Miocene. The migration from the source rock is likely to be largely vertical and possibly along faults before reaching the vuggy, highly permeable reservoirs of the Mishrif Formation. Structural traps in the Mishrif Formation reservoir are likely to have formed in the Late Cretaceous.

Download Full-text

Stratigraphy and Depositional Environment of Mauddud Formation in Ratawi Oil wells of Southern Iraq

IOP Conference Series Earth and Environmental Science ◽

10.1088/1755-1315/877/1/012030 ◽

2021 ◽

Vol 877 (1) ◽

pp. 012030

Author(s):

Maha Razaq Manhi ◽

Hamid Ali Ahmed Alsultani

Keyword(s):

Deep Sea ◽

Lower Cretaceous ◽

Depositional Environment ◽

Carbonate Platform ◽

Depositional Environments ◽

Oil Wells ◽

Oil Field ◽

Microfacies Analysis ◽

Thin Sections ◽

Southern Iraq

Abstract The Mauddud Formation is Iraq’s most significant and widely distributed Lower Cretaceous formation. This Formation has been investigated at a well-23 and a well-6 within Ratawi oil field southern Iraq. In this work, 75 thin sections were produced and examined. The Mauddud Formation was deposited in a variety of environments within the carbonate platform. According to microfacies analysis studying of the Mauddud Formation contains of twelve microfacies, this microfacies Mudstone to wackestone microfacies, bioclastic mudstone to wackestone microfacies, Miliolids wackestone microfacies,Orbitolina wackestone microfacies, Bioclastic wackestone microfacies, Orbitolina packstone microfacies, Peloidal packstone microfacies, Bioclastic packstone microfacies, Peloidal to Bioclastic packstone microfacies, Bioclastic grainstone microfacies, Peloidal grainstone microfacies, Rudstone microfacies. Deep sea, Shallow open marine, Restricted, Rudist Biostrome, Mid – Ramp, and Shoals are the six depositional environments in the Mauddud Formation based on these microfacies.

Download Full-text

Geochemical and biomarker characteristics of crude oils and source rock hydrocarbon extracts: An implication to their correlation, depositional environment and maturation in the Northern Western Desert, Egypt

Egyptian Journal of Petroleum ◽

10.1016/j.ejpe.2015.06.009 ◽

2016 ◽

Vol 25 (2) ◽

pp. 263-268 ◽

Cited By ~ 3

Author(s):

Mohamed M. El Nady ◽

Naglaa S. Mohamed ◽

Lobna M. Sharaf

Keyword(s):

Source Rock ◽

Depositional Environment ◽

Western Desert ◽

Crude Oils

Download Full-text