Water Permeability Reduction Under Flow-Induced Polymer Adsorption
Authors: Ogunberu A.L. , Asghari K. 
Published: March 2010

The influence of induced polymer adsorption for reducing the effective permeability to water in reservoirs is investigated. Previous studies on polymer adsorption in porous media have shown that a static adsorption regime exists at low shear rates of injection. This results in a thin polymer layer whose capability to reduce water permeability is marginal. However, polymer injection at increasing shear rates has revealed an increase in the adsorbed polymer layer and, consequently, improved water permeability reduction. Here, results from sandpacks are presented to show that at increased shear rates, there is improvement in the adsorbed polymer layer. This phenomenon is known as "flow-induced adsorption." The experiments indicate that above a critical shear rate, there is a shift in the permeability-reduction mechanism from static to flow-induced adsorption, necessitating a sharp increase in the adsorbed polymer layer. All results revealed that the critical shear rate for this polymer is about 300 s-1 in the absence of mechanical degradation. This critical shear rate defines the optimal rate of polymer injection for better economic viability of the process. The findings of this study improve the current understanding f the mechanisms involved during polymer squeeze operations and therefore will assist in developing better injection processes with improved chances for success.

Introduction and Background

Increased water production with produced oil is a growing concern in the petroleum industry. The breakthrough of either formation or injected water results in accelerated decline in oil production, increased operational cost of pumping, as well as treatment and disposal of produced water. The need to curtail excess water production without affecting oil production has led to the use of polymers to reduce the permeability to water much more than the permeability to oil. This is essential in wells where water and oil are being produced from the same zone; hence, the waterbearing zones cannot easily be isolated.

In many cases, direct injection of polymers in production wells has proven to be an efficient method to prevent excessive water production(1, 2). To understand the mechanisms that enable water permeability reduction, many experimental studies have investigated the resulting effect of polymer injection on two-phase flow in porous media(3–6). All the studies indicate a selective action of the polymer with a significant reduction in the relative permeability to water with respect to the relative permeability to oil. Based on the fact that the wall effect is the dominant action of the polymer, polymer adsorption thus plays a significant role in relative permeability modification, resulting in permeability reduction of porous media. The objective of polymer adsorption in production wells is to reduce water production without damaging oil productivity. This is critical to the success of near-wellbore conformance treatments in production wells if the hydrocarbon-productive zones cannot be protected during placement(7).

Results of field treatments have varied widely, but often no obvious reason can be given for the success or failure of the treatment. The extent to which relative permeability is modified is governed by the degree of polymer adsorption within the porous medium under consideration.