Geochemical comparison of oils and source rocks from Barents sea by GC methods
Dimitrios Rallakis, Raymond Michels
GeoRessources -UMR 7359 CNRS, Université de Lorraine, CREGU, Faculté des Sciences et Techno-logies, 54506 Vandoeuvre, Nancy, France.
This study aims to determine by means of Gas-Chromatography techniques, the maturity, the weathering biodegradation and the organic facies of a series of source rock and oil samples, recovered from the western Barents Sea, offshore Norway. The database is composed of twelve (12) source rock (SR) core samples plus one (1) from outcrop onshore Svalbard and ten (10) oil samples, representing liquid hydrocarbons from exploration wells. The main objective is to evaluate if the source rock (SR) samples, ranging from Permian to Cretaceous, are reasonable analogues for the SR of any of the oils, ranging from Permo-Carboniferous to Jurassic, and also as a help in overviewing the maturity of the oils. The present study makes use of applied gas-chromatography techniques, by interpreting GC-MS and GC-FID chromatograms. The idea is to calculate a set of biomarker and non-biomarker parameters out of the chromatograms and then make cross-plots that will indicate the terms of maturity, organic facies and biodegradation, between the studied dataset. The maturity assessment based on both the biomarker and the medium range parameters suggests that the studied SR range from immature to post-mature, whereas the studied oils have about the same degree of maturity and are late mature, which could indicate in reservoir mixing processes (blended oils). The organic facies signatures of the oils suggest SR deposition in transitional, marine to estuarine environments (type II kerogen). The SR samples appear to contain type II and III kerogen, indicating transitional and deltaic-fluvial settings. The majority of the SR samples appear weathered (UCM signatures) in contrast to the oils. Finally, the study proposes links between the studied oils and SR samples and attempts to explain the filling pattern (secondary migration) between the SR and the reservoirs.
Key words : hydrocarbons, gas-chromatography, maturity, organic facies, biodegradation.