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Abstract:
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The purpose of this work is to frame the main issues one must face in the design of a mobility control process using polyacrylamide and related acrylic polymers under hostile conditions . Proper preliminary lab evaluation techniques , chemical degradation and related calcium tolerance issues , thermal degradation , and economic optimization based upon injectivity are discussed . Emphasis is placed on stability under alkaline conditions , the use of sodium dithionite to prevent thermal degradation , and the beneficial use of in -situ hydrolysis to increase injectivity . Filtration properties are a focus of screening experiments , and though it often takes several days to achieve acceptable filter ratios in the lab , experience from two field observations indicate that even high molecular weight polymers have filtration ratios on the order of 1 .2 or less before they are injected , so preparation procedures that do not result in this may not yield results that scale to the field . Chemical stability issues with acrylamide polymers are addressed in two parts , the first describing the kinetics of hydrolysis under neutral and alkaline conditions and the second estimating the calcium tolerance of aged polymers using industrial and lab produced analogues . Under alkaline conditions , hydrolysis is very rapid , even at low temperatures . Though aged copolymers of acrylamide (AM ) and 2 -acrylamide 2 -methyl propane sulfonate (AMPS ) exhibit similar calcium tolerances to similarly aged polyacrylamide (PAM ) , viscosity loss is much higher for the latter as this limit is approached . Thermal , or "oxidative" degradation , is examined using Pourbaix diagrams for iron to understand the commonly reported relationships between pH , Eh , and stability . The beneficial effects of sodium carbonate and sodium dithionite on polymer solutions as well as some inconsistencies in the literature point towards a catalytic role played by ppb level amounts of iron in oxidative degradation mechanisms . It is put forward that addition of sodium dithionite is a conservative approach to all acrylic -backboned polymer floods , and practical issues related to this are discussed . A simple analytical model is developed to take a brief look at economic optimization of polymer viscosity , and this is used to demonstrate the benefits of in -situ hydrolysis in alkaline or high -temperature floods . |