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Stratigraphy, diagenesis and petroleum reservoir potential of the Cretaceous Haida, Skidegate and Honna formations, Queen Charlotte Islands, British Columbia

University of British Columbia

The middle to Upper Cretaceous Queen Charlotte Group is composed of mainly marine shales, sandstones and conglomerates which are subdivided into the Haida, Skidegate and Honna Formations. Total stratigraphic thickness of the Queen Charlotte Group is up to 1700 m. Sandstone and conglomerate dominate the succession and offer some petroleum reservoir potential. The Haida Formation (Albian) is a fining upwards, transgressive succession, which rests unconformably on older rocks. It consists of a basal planar and trough cross-stratified, pebbly sandstone to granule conglomerate unit up to 190 m thick interpreted as fluvial deposits, overlain by 700 m or more of fine to very fine sandstone beds, individually 0.5 to 3 m thick, exhibiting bioturbation and hummocky cross-stratification. The Haida Formation grades upward into at least 200 m of concretionary shale of the Skidegate Formation (Cenomanian-Santonian). The Honna Formation (Coniacian-Santonian), which succeeds unconformably and probably also interfingers with the Skidegate Formation, is locally thicker than 800 m, and is dominated by clast supported pebble to cobble and occasionally boulder conglomerate. Conglomerate beds are sharp based, variably graded, and up to 5 m thick. The depositional environment of the Honna Formation was a marine fan-delta or submarine canyon and fan system passing upward to Cretaceous mudstones and rare subaerial volcanics. Primary grain composition, together with diagenesis, determine the reservoir potential of the Queen Charlotte Group. The pebbly basal part of the Haida Formation has the best reservoir potential, due to high quartz framework grain content which restricts precipitation of authigenic phases. Diagenesis of Queen Charlotte Group sandstones involved carbonate precipitation and dissolution, and the growth of iron-rich chlorite, trioctahedral smectite and mixed-layer phyllosilicates, creating a complex paragenetic sequence. Appreciable secondary porosity development, combined with preservation of intergranular primary porosity, results in visual porosity locally exceeding 15% in the basal Haida. Younger sandstones and conglomerates of the Queen Charlotte Group exhibit uniform diagenetic trends throughout all major outcrops on the Islands, and are generally considered poor reservoir prospects.

Text

2010-08-16

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http://hdl.handle.net/2429/27424

Geological Sciences

University of British Columbia

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