Mixing of halite brines with meteoric water in the Clarke Lake gas field, Canada

Formation water samples from the Middle Devonian Slave Point Formation in the subsurface of northeastern British Columbia, Canada, were collected from producing gas wells in the Clarke Lake field. Stable and Sr-isotope data, ionic compositions, and circumstantial evidence show that (i) a “halite brine” end member originated during the Late Devonian and was retained in the Slave Point Formation; (ii) meteoric water recharged from the Rocky Mountains after the Laramide Orogeny in the southwest, flowed through the Devonian aquifer system northeastward, and mixed with the halite brine in the Clarke Lake region. Trapping of hydrocarbons was controlled mainly by the configuration of the Slave Point platform margin relative to the structural tilt, which provided closure in many locations. The regional flow pattern of the meteoric water did not change the trap locations, as it was directed structurally updip, but it probably modified trap capacity in several pools.