Colleen Fitzgerald

The Jeanne d'Arc Basin was formed during Late Triassic to Early Cretaceous time by two episodes of rifting that caused repeated movement on one set of basin-forming faults. This resulted in up to 14 km of sediments, some of which contain huge reserves of hydrocarbons. The Hibernia member, the subject of this thesis, is a sandstone dominated zone within this basin-fill that contains a high proportion of the discovered hydrocarbons.

The Hibernia member is a result of two simultaneous and related events during Tithonian to Berriasian time: 1. deep erosion of upthrown sides of the fault blocks, and 2. a global eustatic rise of sea-level. The provenance and depositional environment are interpreted from the examination of cores, cuttings, microfossils, and thin sections. The siliclastics were derived from a southern source of sediments and sedimentary rocks that had an original metamorphic origin. They were deposited in a non-marine to brackish water environment of channels and associated floodplains in an anastomosed fluvial system. Rates of sedimentation of subsidence were high, and coupled with a contemporaneous eustatic rise resulted in rapid and thick aggradation.

The center of the basin currently has the highest geothermal gradient and thinnest oil window. Burial and thermal history curves show that the source rocks reached maturity first at the Ben Nevis well; early-formed hydrocarbons may have been lost during tectonic movements in Albian time. The source rocks underlying the Hibernia field are presently at peak oil-generating capability. Organic acids formed during the maturation of organic matter have produced excellent secondary porosity in the sandstones of the Hibernia field. However, at Ben Nevis, subsequent thermal degradation of carboxylic acids allowed late-stage cementation by ferroan calcite cement, destroying the reservoir rock.

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Pages: 160
Supervisor: Paul E. Schenk