The Clarke Lake gas field, near the town of Fort Nelson in northeast British Columbia, contains major reserves of dry gas in the Middle Devonian Slave Point Formation. The field was the first of a series of similar discoveries in northeast British Columbia which indicate the presence of a new major gas area. They are shut in awaiting a pipeline connection.

The stratigraphic section in the Clarke Lake field consists of glacial drift and Cretaceous, Mississippian, and Devonian marine rocks overlying a quartzite "basement" which is probably Cambrian or Precambrian in age. The Middle Devonian consists of four laterally equivalent stratigraphic sequences, each present in a different part of the area. These are: (1) a barrier reef belt, now largely dolomitized within the field itself; (2) a shelf or lagoonal area at the south; (3) a shale basin area north of the field; and (4) the area of the Klua embayment, characterized by a tongue of basinal dark shales which extends into the reef and shelf areas and for which the name Klua Formation is proposed. The Horn River Formation of the basin area is subdivided into three members for which the name Muskwa, Otter Park, and Evie are proposed.

Structurally the beds in the Clarke Lake area dip gently south to southwest, but the contact of the Middle Devonian carbonate and shale facies dips steeply north on the north flank of the field.

Present porosity and permeability in the field are controlled entirely by the pattern of dolomitization with the barrier reef belt. Pay thicknesses in the field average 200 feet and range up to 360 feet. Absolute open-flow rates range from 50 to 105 million cubic feet per day per well.