A process for conditioning of wastewater treatment brines for deep well injection during recovery of heavy hydrocarbon oils in situ. High pressure steam is used to mobilize oil, which is recovered in a mixture of oil and produced water. The produced water is pre-treated by removing residual oil. The remaining water is acidified and steam stripped to remove non-hydroxide alkalinity and non-condensable gases, and is then fed to a crystallizing evaporator, where it is evaporated from a circulating brine slurry to produce (1) a distillate stream having a trace amount of residual solutes, and (2) evaporator blowdown stream containing, as dissolved or suspended solids, substantially all of the solutes from the produced water feed. The distillate stream is used as boiler feedwater, either directly or after polishing. The evaporator blowdown is conditioned to remove substantially all suspended solids and to produce a clear brine solution for deep well injection.