Industrial Application for the Removal of Kinetic Hydrate Inhibitor (KHI) Co-Polymers from Produced Water Streams

Abstract

Abstract To avoid hydrate formation, Kinetic Hydrate Inhibitor (KHI) is injected into the upstream wet gas pipelines. KHI eventually remains in the produced water which is treated for H2S and oil removal before it is re-injected into deep disposal wells. Industry regulators in the State of Qatar have concluded that the presence of KHI polymers in the injected wastewater leads to long term reservoir damage… Hence it is essential to remove KHI polymers from re-injected wastewater streams. As there are no industrially proven technologies for removal of KHI, pilot tests were conducted for removal via evaporation. At the same time, futher options were being assessed by other operators, including Wet Air Oxidation and KHI replacement with MEG. All options were assessed on technical, economical, planning, environmental, and safety criteria. The evaporation technology was found to be most suitable. The pilot tests showed that KHI can be removed via evaporation to produce a distillate stream, equal to more than 99% of the incoming flow, with KHI polymers residual concentration lower than the detection limit of 25 mg/l, which will be suitable for re-injection; plus a concentrate stream that includes the concentrated KHI polymers and other salts and solids. The process scheme was developed during the FEED (Front End Engineering and Design) stage, as follows. First, a pre-treatment step ensures breaking of the emulsions and the removal of oil and sludge. This mainly consists of coagulation and pH adjustment tanks, Dissolved Air Flotation and centrifuge packages. This is followed by a two-stage evaporator package which incorporates mechanical vapor recompression, cross heat exchangers, coolers, and cleaning in place techniques. Two outlet streams are created as a result; one distillate stream (free from KHI) which is sent for deep well injection, and one concentrate stream (with KHI), which will be sent to the concentrate storage facilities and will be loaded onto trucks for incineration by a third party. The removal of KHI from produced water streams using evaporation technology has never been done on an industrial scale. The success of this project would ensure that continuing the utilization of KHI products to avoid hydrate formations in the wet gas streams is suitable for the natural gas industry, whilst also avoiding any potential damage of the reservoirs in the long term.