The Cretaceous Cardium Formation, Alberta, Canada, produces oil and gas from thin sandstone stratigraphic traps. The formation can be subdivided into the Cardium sand and overlying Cardium zone. Over a 4,000 mi² (10,000 km²) study area, the Cardium zone decreases in thickness from 80-120 ft (24-36 m) in the northwest to about 40 ft (12 m) in the east. Sandstone beds, some of which are stratigraphic traps, are interbedded with shale in the thicker northwest section. Sandstone beds are absent toward the east. The underlying Cardium sand increases in thickness from about 40 ft (12 m) in the west to 160 ft (48 m) in the east; this increase in thickness corresponds to an increase in shale and decrease in thick-bedded sandstones.

An analysis of 97 seismic lines in the study area indicates that two major seismic reflection patterns comprise the Cardium Formation seismic interval. One pattern consists of two seismic reflections spaced 20-40 msec apart, and the other pattern consists of a single reflection. These two patterns can be mapped across a large area. The areal distribution of the double seismic reflection pattern corresponds approximately to the occurrence of sandstone beds in the Cardium zone.

Reflection patterns of 26 synthetic seismograms generated from sonic logs are comparable to the reflection patterns observed on the field seismic data. This relationship allows interpretation of the field seismic records in terms of stratigraphic characteristics. Thickness of the Cardium zone and distribution of sandstone beds in the Cardium zone control the seismic reflection patterns. The double reflection pattern occurs where the Cardium zone is greater than 80 ft (24 m) thick and contains sandstone beds; one reflection is generated at the interface of the Cardium zone and an overlying shale, whereas the other reflection is generated at the interface of the Cardium zone and Cardium sand. The single reflection pattern occurs where the Cardium zone is less than 80 ft (24 m) thick and lacks sandstones. Because the seismic reflection patterns are regionally mappable units, seismic reflection character analysis can be used to highgrade areas for prospect generation and to depict the trend of potential stratigraphic traps.

This study further demonstrates that sandstone stratigraphic traps and associated facies can be more accurately mapped using a combination of well logs and field seismic records than by using well control along.