Organic-geochemical characterization and correlation of crude oils samples from the most significant oil fields in the Sirte basin, Lybia

Abstract

Ova doktorska disertacija sastoji se od dve jasno definisane celine. U prvom delu ove teze vrednosti parametara izračunatih na osnovu raspodela i obilnosti odabranih pentacikličnih terpana u sirovim naftama iz Libije i Srbije, koji su originalno dobijeni iz rezultata gasno hromatografsko – maseno spektrometrijske (GC-MS) analize upoređene su sa kvantifikacionim rezultatima koji su zasnovani na gasno hromatografsko – maseno spektrometrijsko – maseno spektrometrijskoj (GC-MS-MS) analizi. Analizirani parametri su najčešće korišćeni terpanski izvorni i maturacioni parametri, koji su primenjeni na veliku grupu uzoraka od 70 sirovih nafti, koje potiču iz pet naftnih polja. Cilj je bio da se ispita u kojoj meri se merenja odabranih parametara ovim dvema tehnikama slažu i da se odredi uticaj razlika između vrednosti ovih parametara na geohemijsku interpretaciju. U tom cilju, korišćene su dve statističke metode: koeficijent slaganja korelacija i dijagram srednja vrednost-razlika. Dobijeni rezultati pokazuju da izračunavanje C2718α(H)-22,29,30-trisnorneohopan/(C2718α(H)-22,29,30- trisnorneohopan + C2717α(H)-22,29,30- trisnorhopan), C2918α(H)-30- norneohopan/C2917α(H)21β(H)-30-norhopan i C2917α(H)21β(H)-30- norhopan /C3017α(H)21β(H)- hopan odnosa bilo GC-MS ili GC-MS-MS tehnikom ne utiče značajno na interpretaciju. S druge strane, određivanje C3017β(H)21α(H)-moretan/C3017α(H)21β(H)-hopan odnosa, gamaceranskog indeksa i oleananskog indeksa GC-MS ili GC-MS-MS tehnikom može značajno uticati na interpretaciju. Ove razlike se mogu objasniti koeluiranjem i preklapanjem pikova tokom GC-MS analize ali takođe i boljim razdvajanjem, većom preciznošću i boljom selektivnošću GC-MS-MS tehnike. Odstupanje skoro svih parametara od linije jednakosti je slično za nafte iz istog naftnog polja ali su uočene razlike pri analizi nafti iz različitih naftnih polja. Stoga, kada se planira primena GC-MS-MS rezultata u organsko geohemijskim interpretacijama, preporučuje se i regionalna kalibracija odnosa između GC-MS i GC-MS-MS rezultata za svaki naftni sistem...

This thesis consists of two dinstictive parts. In the first part of this thesis the values of parameters calculated from distributions and abundances of selected pentacyclic terpanes in crude oils from Libya and Serbia, which were originally derived from gas chromatography-mass spectrometry (GC-MS) were compared with quantification results based on gas chromatography-mass spectrometry-mass spectrometry (GCMS- MS). The parameters analyzed are the most often used terpane source and maturity parameters, which were applied to a large sample set of 70 oils, originating from five oil fields. The aim of the paper was to investigate to which extent the measurements of the selected parameters by these two instrumental techniques agree and to determine influence of differences between parameter values on geochemical interpretation. For that purpose two methods, concordance correlation coefficient and mean-difference plot were used. The obtained results indicate that calculation of C2718α(H)-22,29,30-trisnorneohopane/(C2718α(H)-22,29,30- trisnorneohopane + C2717α(H)-22,29,30-trisnorhopane), C2918α(H)-30- norneohopane/C2917α(H)21β(H)-30-norhopane and C2917α(H)21β(H)-30- norhopane/C3017α(H)21β(H)-hopane ratios either by GC-MS or GC-MS-MS do not significantly influence interpretation. On the other hand, determination of C3017β(H)21α(H)- moretane/C3017α(H)21β(H)- -hopane ratio, gammacerane index and oleanane index by GC-MS vs. GC-MS-MS could notably affect interpretation. These differences can be explained by coelution and peak overlapping in GC-MS but also by better separation, higher precision and better selectivity of the GC-MS-MS. Deviation of the almost all studied parameters from the line of equality was similar for the oils from the same oil field but some differences were observed for the oils from different oil fields. Therefore, when GC-MS-MS results are to be used in organic geochemical interpretations, a regional calibration of GC-MS vs. GC-MS-MS relationship for each petroleum system is highly recommended...