Detailed Architecture of a Basin-Floor Sheet-Like Deposit: Neoproterozoic Upper Kaza Group, British Columbia, Canada

Longuépée, Hugues¹, Viktor Terlaky¹, W.R.C. Arnott¹ (1) University of Ottawa, Ottawa, ON

Knowledge of the detailed architecture of deep-sea, sheet-like hydrocarbon reservoirs is limited by the resolution of seismic data, the distance between subsurface wells, and the typically narrow exposure of outcrop analogs. These limitations are minimized in strata of the Neoproterozoic Upper Kaza Group where continuous exposure of glacially-polished strata enabled the detailed mapping of an 800 meter wide by 120 meter thick window.

Several large- and small-scale features that might influence reservoir quality in basin-floor, sheet-like deposits were recognized. The large scale "sheet-like" morphology commonly attributed to basin-floor deposits is present. Several 5- 25 meter-thick sandstone sheets are intercalated with 5-15 meter-thick, fine-grained intervals. There is a lack of major erosion features and sandstones, like fine-grained units, extend laterally over the width of the outcrop.

Internally sand sheets consist of laterally continuous meter-thick, graded or massive sandstone beds separated by irregular erosion surfaces. Erosion causes bed to be amalgamated except where locally separated by thin discontinuous Tcde turbidites. In contrast, the thick fine-grained layers are more complex. Thin Tde turbidites are intercalated with thin upper division sandy turbidites with limited lateral extent. Injections and syn-depositional breccias are common. Erosion surfaces less than 50 cm deep were observed

These data suggest that the common perception that sandy basin-floor deposits consist of a layer-cake stacking of beds and their composite stratal elements may be too simplistic. Although the assumed general morphology appears to be close to reality, a complex history of erosion, injection and loading could lead to more complex reservoir conditions.