Geochemical characterization of crude oils from the Sharara-C oil field, Murzuk Basin, southwestern Libya

[R. M. Saheed]

65 str.

Hemija - Primenjena hemija / Chemistry - Applied Chemistry

Ispitivanja u okviru ove disertacije obuhvatila su nafte iz naftnog polja Šarara-C, basen Murzuk, jugozapadna Libija. Prvi put ove nafte su organsko-geohemijski okarakterisane primenom grupnih korelacionih parametara i specifičnih korelacionih parametara koji se određuju na osnovu raspodele i obilnosti bioloških markera tipa normalnih alkana, izoprenoidnih alifatičnih alkana, sterana i terpana i raspodele i obilnosti fenantrenskih i naftalenskih izomera. Zbog izuzetno teških, ratnih okolnosti u Libiji, uzorkovanje je predstavljalo posebno složenu fazu. Ono je obuhvatilo obezbeđivanje osnovnih geoloških podataka radi definisanja širih geoloških postavki („geological setting“) neophodnih za uspešnu korelaciju nafta-nafta. Nakon toga sledio je postupak koji obuhvata odvajanje nafte od specifično teže vode i izolovanje frakcija zasićenih ugljovodonika i aromata metodom hromatografije na stubu. Analiza bioloških markera koji se u izolovanim frakcijama nalaze u dominantnoj količini (na primer normalni alkani i izoprenoidni alkani u alkanskoj frakciji), kao i fenantrenskih i naftalenskih izomera (u aromatičnoj frakciji) izvedene su klasičnim instrumentalnim tehnikama kakva je gasnohromatografsko-masenospektrometrijska (GC-MS). Međutim, za analizu onih jedinjenja koja se u nafti, odnosno u njenim frakcijama, nalaze u tragovima bila je potrebna upotreba GC-MS-MS instrumentalne tehnike. Ovaj deo istraživanja urađen je u Geological Survey of Denmark and Greenland. Libija je jedan od najvećih proizvođača sirove nafte. Uprkos ovoj činjenici sirove nafti iz najvećeg broja njenih naftnih polja do sada nisu detaljnije organsko-geohemijski ispitivane. Samim tim nije im potpunije definisano preklo, sredina taloženja, stepen maturisanosti, stratigrafska pripadnost ili stepen biodegradacije. Ispitivane nafte nisu bile izložene biodegradaciji, generisane su iz mešovite terestrijalne/marinske prekursorske biomase, i staložene su u suboksičkoj sredini. Veliki sadržaj tricikličnih terpana, i odnos steran/hopan >1 potvrdili su marinsku sredinu taloženja. Odsustvo oleanana i drugih biomarkera koji potiču od angiospermi ukazalo je na izvorne stene iz doba Jure. Nafte su generisane u glavnoj fazi „naftnog prozora“, sa naznakama da su na njihovu termičku zrelost mogli da utiču i drugi procesi osim termičkog sazrevanja. Radi ispitivaanja organsko-geohemijske homogenosti svih nafti naftnih polja u Libiji, ove nafte su korelisane i sa naftama basena Sirte, koje su geohemijski okarakterisane u ranijim studijama

Investigations within this doctoral dissertation included crude oils from the Sharara-C oil field, Murzuk Basin, southwestern Libya. For the first time, these oils were organicgeochemically characterized using group correlation parameters and specific correlation parameters determined based on the distribution and abundance of biological markers such as normal alkanes, isoprenoid aliphatic alkanes, steranes and terpanes, and the distribution and abundance of phenanthrene and naphthalene isomers. Organic-geochemical investigations began with sampling. In such case, due to the extremely difficult, wartime circumstances in Libya, it represented a particularly complex phase. It included the provision of basic geological data to define the broader geological setting necessary for successful oil-oil correlation. This was followed by a procedure that includes the separation of oil from specifically heavier water and the isolation of fractions of saturated hydrocarbons and aromatics by column chromatography. The analysis of biological markers that are found in a dominant amount in the isolated fractions (for example normal alkanes and isoprenoid alkanes in the aliphatic fraction), as well as phenanthrene and naphthalene isomers (in the aromatic fraction) were performed using classic instrumental techniques such as gas chromatography-mass spectrometry (GC-MS). However, the use of GC-MS-MS instrumental technique was required for the analysis of those compounds that are found in trace amounts in oil, i.e. in its fractions. This part of the research was done in the Geological Survey of Denmark and Greenland. Libya is one of the largest producers of crude oil. Despite this fact, the crude oil from the largest number of its oil fields has not been analyzed organic-geochemically in detail. Therefore, their bilogical precursors, depositional environment, degree of thermal maturity, age or degree of biodegradation has not been more fully defined. The obtained results showed that the examined oils were not exposed to biodegradation, and that they were generated from mixed terrestrial/marine precursor biomass deposited in the suboxic, environment. The high content of tricyclic terpanes, and the sterane/hopane ratio >1 confirmed the marine depositional settings. The absence of oleanane and other angiospermderived biomarkers indicated Jurassic source rocks. The oils were generated in the main phase of the oil window, with indications that their thermal maturity may have been influenced by processes other than thermal maturation. In order to examine the organic-geochemical homogeneity of all the oils of the oil fields in Libya, these oils were also correlated with the oils of the Sirte basin, which were geochemically characterized in earlier studies.

organska geohemija, korelacija naft-nafta, Šarara-C, basen Murzuk, jugozapadna Libija, biološki markeri, normalni alkani, izoprenoidni alifatični alkani, sterani, terpani, izomeri fenantrena i naftalena.

organic geochemistry, oil-oil correlation, Sharara-C oil field, Murzuk Basin, southwestern Libya, biological markers, normal alkanes, isoprenoid aliphatic alkanes, steranes, terpanes, phenanthrene and naphthalene isomers

550.4(612)(043.3)

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