Effective porosity in carbonate rocks in Western Canada reservoirs is, to a large degree, dependent upon favourable post-depositional, particularly diagenetic, processes.

To assist in the search for carbonate rock reservoirs, and in the understanding of post-depositional processes, the geologist has available a wealth of information from recent carbonate sediment studies in such areas as Florida Bay, the Bahamas and the Persian Gulf. This information can be used to interpret the ancient rocks in terms of environments, deposition of the sediments, and the post-depositional changes that occurred during the lithification.

Although each depositional environment may host a relatively few sediment types, post-depositional processes can produce a wide variety of textures in the resultant rock. As carbonate sediments are commonly composed of more than one constituent, and the susceptibility of each constituent to the diagenetic process may vary, the diagenetic history of each sediment type may be exceedingly complex. Often, however, only one or two processes are involved, and the interpretation is relatively simple.

A variety of ancient depositional environments and sediment types can be interpreted from a study of cores of the Devonian Swan Hills, Rainbow, and Zama rock units. Diagenesis of some of these sediments has resulted in highly porous carbonate rocks that form the productive reservoirs in Northern Alberta. Although a number of different processes were involved, selective dolomitization and subsequent selective leaching were the dominant processes. To illustrate the development of the reservoir, and the processes involved, selected samples from cores of these three members are displayed and illustrated.

As the development of a porous reservoir from a sedimentary facies is so dependent upon diagenesis, and the geometry of the reservoir is often determined by the pattern of diagenesis, an understanding of these processes seems prerequisite to location and exploitation of this type of reservoir.

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