Synthetic Polymer Friction Reducers Can Cause Formation Damage
Authors: Woodroof Robert A. , Anderson Robert W. 
Published: December 2007

In selecting friction reducers for acid stimulation applications, stability considerations are often overlooked. This paper will discuss the factors which affect the stability of these polymeric materials in hydrochloric acid. Such factors as temperature, pH, presence of oxidizing and reducing agents, and compatibility with other acid additives will be considered. Chemical explanations for the resulting instabilities will be contrasted with chemical structures for modified vinyl copolymers which provide increased stability.

Documented field consequences of these polymeric instability problems will be highlighted, along with field experience for some of the new, more stable, modified vinyl copolymers.

Introduction

The phenomenon of drag reduction in turbulent flow was first noted during the second world war, apparently arising in connection with the development of flame warfare weapons. The drastic reduction of fluid friction by the addition of small quantities of long-chain high molecular weight polymers to water has been extensively studied by the U. S. Navy.

The flow properties of dilute polymer fluids, as well as the relation between the chain length of the polymers and their drag reduction performance, were first studied in the early 50's to mid 60's, during which time interest in petroleum industry applications of these materials was kindled. It was observed that the increased flow achieved by the incorporation of these polymeric additives in oil well treatment fluids resulted in higher injection rates, lower horsepower requirements, large reductions in pumping costs, and more efficient fracturing operations.

The early dry solid friction-reducing polymers found applications in many aqueous fracturing treatments. Some natural polymers and modified cellulose materials, as well as a number of synthetic polymers, were also found to be suitable for use in polymers, were also found to be suitable for use in acid fracturing fluids. Advances in polymerization techniques made possible the development of synthetic polymers in liquid form, thus averting one of polymers in liquid form, thus averting one of the early shortcomings of the dry solid polymers, namely, lumping, and the consequent excessive concentrations required to compensate for their slow hydration rates. The liquid polymers provided the added benefit of more uniform metering.

It has become apparent in recent years that in selecting the appropriate friction reducers for acid stimulation applications, polymeric stability considerations are often overlooked in favor of ease of handling and hydration rate considerations. This paper will provide a brief survey of some of the more paper will provide a brief survey of some of the more frequently employed synthetic acid friction reducers, the factors that affect their stability in hydrochloric acid, a documented use history of a synthetic polymer instability problem, and an introduction to some of the more acid-stable, modified, synthetic polymers.

SURVEY OF ACID FRICTION REDUCERS

Most friction reducers have a few properties in common. They are high molecular weight polymers which tend to build non-Newtonian gel structure. To varying degrees, they tend to be shear sensitive and susceptible to chemical and thermal degradation. Chemicals capable of causing polymer degradation include acids and bases, oxidizing agents, and enzymes. Most common polymers thermally decompose at temperatures in excess polymers thermally decompose at temperatures in excess of 450 degrees F in an inert atmosphere at neutral pH. Increasing the temperature tends to enhance the degradation actions of the aforementioned chemicals.

There are many theories regarding the mechanism of fluid friction reduction. One such theory states that when these polymeric materials are hydrated in a fluid system, they arrange themselves in a random pattern and increase the viscosity of the resulting pattern and increase the viscosity of the resulting solution.