Experimental Investigation of Polymer Induced Fouling of Heater Tubes inthe First-Ever Polymer Flood Pilot on Alaska North Slope

摘要

Polymer flooding has been validated in the lab and by successful applications in other countries,such asCanada and China,to be an effective EOR technique for heavy oil reservoirs.Currently,polymer flooding isbeing pilot tested for the first time in the Schrader Bluff viscous oil reservoir at Milne Point field on AlaskaNorth Slope(ANS).One of the major concerns of the operator is the impact of polymer on the oil productionsystem after polymer breakthrough,especially the polymer induced fouling issues in the heat exchanger.This study investigates the propensity of polymer fouling on the heater tubes as a function ofdifferent variables,with the ultimate goal of determining safe and efficient operating conditions.A uniqueexperimental set-up was indigenously designed and developed to simulate the fouling process on the heatingtube.The influence of heating tube skin temperature,tube material,and polymer concentration on foulingtendency was investigated.Under each test condition,the test was run five times with the same tube,andin each run,the freshly prepared synthetic brine and polymer solution were heated from 77°F to 122°F tomimic field operating conditions.The heating time and fouling amount were recorded for each run.Themorphology and composition of the deposit samples were analyzed by environmental scanning electronmicroscopy(ESEM)and X-ray diffraction(XRD),respectively.It has been found that,in general,the presence of polymer in produced fluids would aggravate the foulingissues on both carbon steel and stainless steel surfaces at all tested skin temperatures(165°F,250 °F and350°F),but only higher skin temperatures of 250°F and 350°F could cause polymer induced fouling issueson the copper tube surface and the fouling tendency increased with polymer concentration.At the lower skintemperatures of 165°F,no polymer-induced fouling was identified on the copper tube.A critical temperaturethat is related to the cloud point of the polymer solution was believed to exist,below which polymer inducedfouling would not occur and only mineral scale deposited,but above which the polymer would obviouslyaggravate the fouling issue.The heating efficiency of the tube would be reduced gradually as more foulingmaterial accumulates on its surface.The ESEM results indicate that if polymer precipitated and depositedon the surface,it would bond to the mineral crystals to form a stronger three-dimensional network structure,and that is why the polymer induced fouling was tougher and more difficult to be removed from the tubesurface.The XRD analysis results confirm that the presence of polymer in the fluids can enhance the mineralscale propensity.The study results have provided practical guidance to the field operator for the ongoingpolymer flooding pilot test on ANS.This study may also prove to be valuable for other chemical EORprojects around the world.