Abstract

In this article, we examine the controls on gas production from Cretaceous clastic strand-plain deposits in an area (the Deep Basin of Alberta) that was instrumental in the development of the basin-centered gas concept. By integrating core, wireline logs, three-dimensional seismic data, petrophysical measurements, pressure, and production data, we show that the best gas production comes from stratigraphic sweet spots consisting of chert-rich shoreface and beachface deposits that alternate between tight quartzose sandstone. The physical properties of the chert-rich and quartzose units are sufficiently different that they can be distinguished seismically. Seismic modeling and observations show that high-amplitude areas correspond to porous (and productive) chert-rich shoreface and beachface deposits. A map of seismic amplitudes for the Cadotte Member shows narrow (∼0.5 km [0.3 mi] width), curvilinear, high-amplitude anomalies (corresponding to cherty shoreface and beachface deposits) that are parallel to depositional strike (east-northeast–west-southwest) and correlate precisely with production trends. Wells drilled outside the high-amplitude anomalies do not have sufficient permeability to produce gas at economic rates. The shore-parallel stratigraphic sweet spots are locally compartmentalized by shale-filled channels that cut at high angles through the strand plain. Like other Cretaceous units in this area, the Cadotte Member is wet structurally updip from gas-charged rocks. The contact between these two phases traversing through our study area and its location is controlled by the interplay of regional structural dip and depositional processes that controlled the lithology and stratigraphic architecture of the rocks.

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