Investigation Into Colloidal Polysaccharides As Kinetic Hydrate Inhibitors

Kinetic hydrate inhibitor?KHI?has been widely applied for hydrate management in oil&gas industry.KHI can retard hydrate nucleation and reduce hydrate growth within a certain subcooling temperature.However,the difficulty in biodegradation restricts its field applications.In this paper,colloidal polysaccharides are selected as KHIs based on the principle of environmental friendliness.Hydrate inhibition performance of selected polysaccharides are evaluated and their tolerance to sour gases as well as salts are tested.In this work,biodegradability of three colloidal polysaccharides,i.e.guar gum?GG?,xanthan gum and carrageenan are measured with BOD₅/COD.The result demonstrates that colloidal polysaccharides is biodegradable with 30%biodegradability.Tolerant subcooling temperature?TST?of three polysaccharides are also tested.The results prove GG the best KHI among three polysaccharides with 7.36 ^oC TST.Accordingly,cationic gaur gum?CGG?are selected for further investigation due to its improved viscosity and solubility.Furthermore,the performance of CGG and three commercial KHIs are compared.Experiments are performed in natural gas atmosphere of 8.2 MPa.CGG is the best inhibitor in the nucleation period with 10.31 ^oC TST which is 6.57 ^oC,1.06 ^oC and 1.67 ^oC higher than HN19,HY121 and VC-713 respectively.As for growth process,CGG extends the completed inhibition region?CIR?less effective than commercial inhibitors do,but in higher subcooling condition where other inhibitors absolutely lose their inhibition performance,CGG still shows inhibition effectiveness slowing crystal growth.CGG lose its performance outright when the subcooling temperature reaches 11.38 ^oC.Comparing with the temperature where HN19,HY121 and VC-713 are totally disabled,it increases by 5.66 ^oC,2.79 ^oC and 2.69 ^oC respectively.Additionally,it is investigated the how salts and sour gas impact to the performance of polysaccharide and its derivative.The results prove that NaCl with low concentration would weaken the performance of GG and CGG during nucleation by reducing their TST,but it would strength the performance as NaCl concentration increases.Similar trend occurs during the growth region.Sour gas strongly impacts the effectiveness of GG and CGG.As for gas mixture of 60%CH₄ and 40%CO₂,TST increases monotonously when NaCl concentration increases.Memory effect presents in the sour gas system added CGG so that a bit of hydrate grows rapidly and then the growth rate reslows again.It indicates that seleted inhibitors shows significant tolerance to salinity but are negatively impacted by sour gas.In conclusion,polysaccharide is of capability inhibiting hydrate when the salinity is high;but the sour gas would impact its application.