Organic petrological and geochemical appraisal of the Upper Jurassic Naokelekan Formation, Kurdistan, Iraq
Upper Jurassic Naokelekan Formation, being part of the intercepted strata of the well-known Miran oilfield in Kurdistan region of Northern Iraq, has been previously extensively evaluated as a potential/effective source rock, mainly by means of organic geochemistry. In the present study, a total of 60 samples were collected from four Naokelekan Fm. outcrops, those of Banik, Galy-Derash, Barsarin and Dwawa, in order to conduct organic petrographical study and organic geochemical assessment, including both biomarker and Rock-Eval analyses. The average recorded TOC content for Banik, Galy-Derash, Barsarin and Dwawa section is considerable to very high, corresponding to values of 27.5, 9.0, 3.5 and 5.2 wt%, respectively, with the highest values representing the notably organic-rich bottom part of the Formation, known as “coal layer”. According to the petrographical analysis, solid migrabitumens comprise the predominant component for all the analysed samples, whereas the maceral groups of vitrinite, liptinite and/or inertinite showcase a minor to trace occurrence. In terms of organic geochemistry, each of the four sections of interest shows a different biomarker profile. Nevertheless, a number of calculated parameters related to kerogen type and depositional conditions, including the isoprenoids/n-alkanes ratios, suggest a mixed terrestrial-marine organic matter. Furthermore, as indicated by the Ro (%) measurements along with Rock-Eval parameters and the vitrinite reflectance equivalent based on aromatic compounds, the maturity level is marginally mature in the cases of Banik and Galy-Derash, whereas in the cases of Dwawa and Barsarin sections it is mature to post-mature. A synthesis of the organic petrography and geochemical appraisal applied in the present study, suggests that the reported solid hydrocarbons in Naokelekan Fm., particularly at its basal layers are non-indigenous/migrated and the precursor organic matter was deposited in a marine environment, under oscillating conditions ranging from euxinic to well‑oxygenated. Accordingly, the organic features of the notably bitumen-rich “coal-bed” fit the profile of a reservoir and/or migration path.
| Main Authors: | , , , |
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| Other Authors: | |
| Format: | artículo biblioteca |
| Language: | English |
| Published: |
Elsevier
2020-11-07
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| Subjects: | Biomarkers, Bitouminous shales, DOM, Maceral, Maturation, Solid bitumens, Rock-eval parameters, |
| Online Access: | http://hdl.handle.net/10261/233373 |
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| Summary: | Upper Jurassic Naokelekan Formation, being part of the intercepted strata of the well-known Miran oilfield in Kurdistan region of Northern Iraq, has been previously extensively evaluated as a potential/effective source rock, mainly by means of organic geochemistry. In the present study, a total of 60 samples were collected from four Naokelekan Fm. outcrops, those of Banik, Galy-Derash, Barsarin and Dwawa, in order to conduct organic petrographical study and organic geochemical assessment, including both biomarker and Rock-Eval analyses. The average recorded TOC content for Banik, Galy-Derash, Barsarin and Dwawa section is considerable to very high, corresponding to values of 27.5, 9.0, 3.5 and 5.2 wt%, respectively, with the highest values representing the notably organic-rich bottom part of the Formation, known as “coal layer”. According to the petrographical analysis, solid migrabitumens comprise the predominant component for all the analysed samples, whereas the maceral groups of vitrinite, liptinite and/or inertinite showcase a minor to trace occurrence. In terms of organic geochemistry, each of the four sections of interest shows a different biomarker profile. Nevertheless, a number of calculated parameters related to kerogen type and depositional conditions, including the isoprenoids/n-alkanes ratios, suggest a mixed terrestrial-marine organic matter. Furthermore, as indicated by the Ro (%) measurements along with Rock-Eval parameters and the vitrinite reflectance equivalent based on aromatic compounds, the maturity level is marginally mature in the cases of Banik and Galy-Derash, whereas in the cases of Dwawa and Barsarin sections it is mature to post-mature. A synthesis of the organic petrography and geochemical appraisal applied in the present study, suggests that the reported solid hydrocarbons in Naokelekan Fm., particularly at its basal layers are non-indigenous/migrated and the precursor organic matter was deposited in a marine environment, under oscillating conditions ranging from euxinic to well‑oxygenated. Accordingly, the organic features of the notably bitumen-rich “coal-bed” fit the profile of a reservoir and/or migration path. |
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