LITHIUM SILICATE SCALE IN OIL-FIELD STEAM-GENERATION

At Wolf Lake, steam for in situ recovery of bitumen has been generated from produced water for over two years. Conventional softening of the produced water with warm lime followed by weak acid cation exchange w ithout silica removal was inadequate to prevent scaling of the boiler tubes. Analysis identified the scale as lithium silicate, a material n ot previously identified as a scale in steam generation. Treatment of the produced water lo lower the silica concentration below 50 mg/L has been found necessary and at 25 mg/L adequate to prevent scaling under the operating conditions at Wolf Lake. The concentration of lithium i n produced waters is expected to vary with the reservoir, and to be a previously unrecognized determinant in the allowable level for silica in boiler feed water.