Reservoir Characteristics of the Late Cretaceous Cardium Sandstones, a Tight Oil Play: West Pembina, Alberta, Canada

The Cardium Formation shoreface sandstones contain one of the largest oil accumulations in Canada; the studied Pembina oil field in west-central Alberta is the largest. Discovered in 1953, initial drilling targeted relatively clean shoreface sandstones and conglomeratic reservoirs. Recent efforts, however, with multistage fractured horizontal wells have targeted relatively low permeable, muddy offshore sandstone reservoirs along the edges of existing pools. The objective of this study is to characterize these unconventional reservoirs.

Core observations along the western Pembina field boundary identified two offshore facies distinguished by the degree of bioturbation and biodiversity as well as bedforms. Facies 1 is characterized by intensely bioturbated muddy sandstone with rarely preserved very fine grained laminated and rippled sandstone beds. Facies 2 is characterized by preserved very fine grained hummocky cross stratified (HCS) and rippled sandstone beds interbedded with intensely bioturbated muddy sandstone. Similar characteristics were observed in outcrops of Cardium sandstones in the Rocky Mountain Foothills. The level of bioturbation and biodiversity is different in these facies as Facies 1 is more bioturbated; Facies 2, however, shows more trace fossil diversity. HCS sandstone beds along with wave and current ripples occur in both facies, although a greater abundance and better preservation of ripples is apparent in Facies 2. Both facies are deposited in an offshore setting between storm and fair weather wave base. The facies exhibit different reservoir properties affected by sedimentology, bioturbation index, trace fossil diversity and sedimentation rates along with storm, tidal, and fluvial influences. Both offshore facies underlie thick fine grained HCS shoreface sandstones and overlie rarely bioturbated rippled and laminated mudstones in areas adjacent and within the Pembina field boundary.

Differentiation of the two offshore facies is key to the development of this large tight oil play as the variations in bioturbation intensity, bed forms, and sandstone bed geometry result in different reservoir properties, i.e. porosity, permeability, flow characteristics, and hydraulic fracture characteristics.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California