Polymers as relative permeability modifiers: adsorption and the dynamic formation of thick polyacrylamide layers

Water production from oil and gas reservoirs is increasing worldwide. as more reservoirs are becoming mature. In order to control water production, polymers and gels are often injected into the formation to reduce the water permeability. These systems are known as relative permeability modifiers. Although these methods sometimes lead to significant cost savings, and many successful treatments have been reported, a wider application is hindered by the lack of understanding of the basic mechanisms of permeability modification by polymers. This paper presents some pore-level and basic studies on polymers, with the aim of providing a better understanding of these systems. Experiments have been performed in micro-scale glass flow models, and atomic force microscopy was used to validate the flow observations. The role of adsorption and flow of polyacrylamides in the formation of thick layers is described. The size of statically adsorbed polyacrylamide layers depends on the polymer characteristics (molecular weight, degree of hydrolysis, salinity, etc.), but is less than 250 nm for all the systems studied. On the other hand, dynamically formed polymer layers can reach several thousands of nanometres. The existence of these thick polymer layers is shown here, to our knowledge for the first time, through flow experiments and AFM measurements. While mechanical retention cannot occur under our experimental conditions, the mechanism of adsorption-entanglement gives a reasonable mechanistic description of the dynamic formation of thick layers. The implications of these mechanisms in the modelling of the flow and selection of polymer systems are discussed. (C) 2004 Elsevier B.V. All rights reserved.