Sedimentology, Ichnology and Reservoir Characterization of the Lower Montney D1 and D2 Horizons, Pouce-Coupe-Dawson Area

Abstract

Over the past decade, the Montney Formation has evolved as western Canada's premier unconventional exploration play. Despite minimal variation in grain size between facies (almost all lithofacies consist of siltstone and very fine-grained sandstone), it has become apparent that primary depositional characteristics play a seminal role in preserved reservoir attributes. In particular, the presence and nature of bioturbation is increasingly recognized as a key element in resource distribution. Bioturbation has long been recognized as a potentially significant control on reservoir properties in both conventional and unconventional reservoir units. The Montney Formation in the Pouce-Coupe-Dawson area in the Alberta-British Columbia border region of western Canada presents an excellent opportunity to investigate the relationship between bioturbation and permeability in a siltstone to very fine-grained sandstone succession. The interval of interest directly overlies the Montney Turbidite interval (a previous conventional unit targeted in the 1990s), and although adjacent stratigraphic successions are dry, it is characterized by liquids-rich natural gas. Fifty cores were logged, focusing on sedimentological and ichnological features. Key cores were analyzed petrographically and porosimetry/permeability measurements obtained in order to assess changes in reservoir characteristics between facies and subfacies. Due to the subtle nature of Montney bioturbation, it is difficult to observe in hand sample. In published literature to date there has been minimal attention focusing on potential effects that bioturbation might have on reservoir properties in the Montney Formation. In the studied core, the most common ichnofabric observed is cryptic bioturbation, which has been recognized throughout the interval and has altered much of the rock fabric. Bioturbation modifies the relationship of kv vs. kh (i.e. ratio approaches 1), and preliminary porosimetry indicates that the bioturbation has had an effect on resource storativity and deliverability. The trace fossils are also useful for subdividing the interval into facies. This coupled with facies associated permeability trends has enabled the development of a predictive framework delineating areas with superior reservoir quality.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016