The Marraat oil discovery on Nuussuaq, West Greenland: Evidence for a latest Cretaceous - Earliest Tertiary oil prone source rock in the Labrador Sea - Melville Bay region

Flemming G. Christiansen, Jørgen Bojesen-Koefoed, Gregers Dam, Hans Peter Nytoft, Lotte M. Larsen, Asger K. Pedersen, T. Christopher R. Pulvertaft

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32 Citations (Scopus)

Abstract

Field work and drilling on the Nuussuaq peninsula, West Greenland in August 1993 revealed the existence of live oil filling vesicles in Paleocene lavas. It was demonstrated that the oil fills most available porosity in the lavas in two fault-bounded zones that can be traced for more than 1 km along strike and several hundreds of metres across strike. Intense oil impregnation was confirmed in the uppermost 86 m of a 448-m deep cored borehole, with scattered traces also in the deeper part. During the 1994 field season the area with oil shows at the surface was found to extend over least 8 × 5 km. The depositional environment and thermal history of the inferred source rock and the post-migration history of degradation have been interpreted from organic geochemical data (extraction, class separation, GC, GC/MS, and carbon isotopes) from core and from surface samples collected throughout this area. From gross compositions, the degradation of the oil is interpreted as varying from very limited to moderate. Steranes, terpanes, and acyclic isoprenoids are unaffected by degradation in all samples and show remarkably constant ratios, suggesting leakage from a homogeneous reservoir. The degradation of n-alknanes does not correlate with the degree of degradation interpreted from the gross composition, and active, replenishment into the structure is suggested, either from an underlying reservoir or by long distance migration from an actively generating source rock. The maturity of the oil corresponds to a source rock in the upper part of the oil window, judging from the high contents of NSOs, low Ts/Tm values and high moretane contents, low methylphenanthrene index and various other biomarker ratios. Hopane isomerization (22S/22S+R) has reached equilibrium whereas 20S/20S+R sterane isomeriza- tion ratios show values between 0.40 and 0.45. A number of characteristics (e.g. high Sa/Ar, high wax, high CPI, high Pr/Ph (4-5), dominance of C29 steranes, low contents of tricyclics and extended hopanes, high contents of phenanthrenes and carbon isotope composition) suggest that the oil-prone material in the source rock is terrestrial in origin but was deposited under marine conditions. This is further substantiated by the high contents of bisnorlupane and oleanane which are typical for latest Cretaceous and Tertiary deltaic source rocks. The implications of this significant discovery are very encouraging for future exploration offshore Labrador, West Greenland and in Melville Bay since it demonstrates for the first time that a source rock capable of generating oil exists in the region, and thereby challenges the 1970s' reputation of the area as being entirely gas-prone.

Original languageEnglish
Pages (from-to)39-54
Number of pages16
JournalBulletin of Canadian Petroleum Geology
Volume44
Issue number1
DOIs
Publication statusPublished - Mar 1996

Programme Area

  • Programme Area 3: Energy Resources

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