Major gas fields in northeastern British Columbia occur in several types of carbonate porosity traps of Middle Devonian age. These traps consist of lenses or "patch reefs" in a shelf environment, barrier reef ridges at the shelf edge, and apparently of isolated bioherms in the adjacent basin. The reef limestones are primarily stromatoporoid rubble. These rocks apparently had high original porosity but, except where dolomitized, are now tightly cemented by calcite. As a result, production is now found only in the dolomitized rocks.

The process of dolomitization is controlled in part by original depositional environment, but is partly independent of original lithology. Exploration for these reservoirs, therefore, requires a study of both depositional environment and the cementation and dolomitization processes.

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