Reservoir Architecture of a Fine-Grained Turbidite System: Lower Triassic Montney Formation, Western Canada Sedimentary Basin
Thomas F. Moslow, 2000. "Reservoir Architecture of a Fine-Grained Turbidite System: Lower Triassic Montney Formation, Western Canada Sedimentary Basin", Deep-Water Reservoirs of the World, Paul Weimer
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The Lower Triassic Montney Formation of west-central Alberta has been widely recognized as the first and only documented turbidite reservoir in the Western Canada Sedimentary Basin. First discovered and exploited in 1993, this play has yielded over 1.5 TCF of gas, plus liquids, and continues to be an active and expanding exploration play. Extensive well and core control provides the basis for constructing a sequence stratigraphic framework and reservoir architecture of these fine-grained sandstone turbidites. Within the lowstand systems tract of the mid-Montney, turbidite channel, lobe/sheet-sand and levee-overbank facies associations are recognized. Reservoir quality and heterogeneity of these facies are predominately a product of hydrodynamic processes of deposition. Subregional syn- or post-depositional extensional tectonism is recognized as playing a significant role in the distribution, over-thickening and orientation of turbidite reservoir facies.
A distinct ramp-”edge” or break-in-slope trends north-northwest/south-southeast and defines the updip depositional limit of turbidite facies. The ramp-edge orientation is fault controlled and marks the onset of rapid and abrupt thickening of lowstand facies associations. Due to the updip headward retreat of turbidite channels, the ramp-edge is highly modified by mass-wasting processes. Turbidite channels coalesce down-dip towards the base of slope and then grade into turbidite lobes basinward. Turbidite channels are associated with significant lateral discontinuity along depositional strike due to cross-cutting and have greater continuity along dispositional dip. Turbidite channel facies associations can be amalgamated to thicknesses of up to 30 m, due to synsedimentary tectonism within localized grabens or half-grabens. The distribution of levee overbank or channel-margin facies associations constrains the width of turbidite channels to a few hundred meters. In addition to inferring proximity, a levee-overbank facies association can be used to infer the direction of the associated turbidite channel through dipmeter log patterns. Turbidite lobes have a broad aerial extent, up to 10 km2 in size, occur at the down-dip depositional limit of turbidite facies deposition and thin and grade basinward to shaly siltstone.