Contemporary geochemical characterization methods for reservoir core bitumen and oil – application to samples from Mid-Norway and the Norwegian Barents sea – source rock facies and maturity assessment & biodegradation effects as measured on inclusion gas and reservoir oil samples.

Abstract

A total of seventy reservoir core samples from nine wells of the Mid-Norway and the Barents Shelf were geochemically analyzed to compare the composition, alteration effects, maturation and organic facies. The analytical techniques, like gas analysis from inclusions and TLC-FID of bitumen samples not only disclose the wet components of hydrocarbons in each well but also mention the parts of reservoir affected by biodegradation from relative fraction of each type of hydrocarbon compounds. The geochemical methods GC-FID, GC-MS reveal the organic facies for the selected wells along with their level of maturation. Gases from inclusions of wells from the Mid-Norway suggested the condensate phase of petroleum at the time of generation shown by relatively dry gases from inclusions while higher wet gases in the Barents Sea indicate the oil system at the time of generation. Higher butane isomers (i-C4/n-C4) from gas inclusions and Iatroscan results discover palaeo-petroleum in the Utgard High owing to high polar fraction, whereas oil phase shown by dominance of saturated compounds in the Barents Sea samples except the well 7321/7-1 showing the alteration effects. The relatively more anoxic conditions prevailed in the samples from the Mid-Norway and lower maturity of the Barents Sea samples inferred from isoprenoids to normal alkane ratios. Mostly the samples from the Mid-Norway and the Barents Sea are labeled as typical Spekk (Hekkingen) marine facies noticed from concentration of steranes and aromatic hydrocarbons. The medium range parameters from GC-MS results define the maturation of samples commonly lie in medium oil window. In addition, selected oil samples from the Norwegian Continental Shelf were studied to apply Thompson and Halpern parameters for light hydrocarbons to characterize the degree of transformation in various oils and correlation of source rock facies that generated the petroleum in these fields. Biodegradation is pronounced in the Heidrun, Gulfaks Sør and Goliat fields while evaporative fractionation predominates in Snøhvit and Midgard fields. Water washing effect can be observed in the Smørbukk and Ula fields. Most of the oils represent to be derived from the same organo facies (Draupne/Spekk/Hekkingen formations).