Study On Hardness Removal Technology For Oilfield Produced Water By CO₂

The produced water of one thick oilfield with high salinity and hardness cannot reach the effluent standard,and it cannot inject an appropriate layer.The built sewage storage pool is unable to meet the requirements soon.This oilfield is located in the arid area where the annual precipitation is 200 mm.And SAGD?Steam Assisted Gravity Drainage?mining technology requires a large number of fresh water as the headwater of thermal recovery stream-injection boiler.Therefore,a new reuse boiler system for wastewater treatment will be built to solve the problem of water shortage and thick oil produced water disposal.This paper use CO₂ in flue gas and alkali as reagent for chemical precipitation and soften water method in order to soften hard water,to solve the problem of high hardness in the thick oil produced water.The wastewater of A and B sewage treatment station in one of The Sinkiang oilfield is the research object of this research,which water quality was comprehensively analysed and the main direction of hardness removal has been confirmed.The indoor simulation experiment was proceeded according to the wastewater quality characters and main influencing factors including the alkali added amount,aeration time,ventilation capacity.Then the pilot technology and plant was designed according to the above results,which would provide reliable parameters for the industrialized application.The pilot tests show that the water hardness could quickly fall below 300mg/L in 2h when the water capacity is 0.5m³/h,the alkali added amount is 4000mg/L and the flue gas flow rate is 10m³/h,which could meet the requirements of hardness to boiler softener make-up water,the CO₂ gas volume and processing water gas water ratio of 2:1.The removal rate of calcium is 98.7%,the Ca²⁺concentration is 20.39mg/L,the total hardness fell to 233.6mg/L,and the CO₂ gas effective availability is 25%.