Reservoir Stability of Polymer Solutions
Authors: Knight Bruce L. 
Published: December 2007

A study was made of the specific effects of oxygen, oxygen inhibitors, temperature, and water salinity on a commercially available polyacrylamide used in oil recovery. Because oxygen greatly effects solution stability, particular attention was given to oxygen inhibitors, with emphasis on particular attention was given to oxygen inhibitors, with emphasis on sodium hydrosulfite and formaldehyde. For a number of reasons, the latter is found to be more desirable for the purpose.

Introduction

Adequate mobility control between fluid banks is a significant factor in the successful application of secondary and tertiary oil recovery processes. Reservoir flooding when the mobility of displacing fluids equals or is lower than the mobility of displaced fluids increases recovery efficiency by virtue of improved pattern conformance. pattern conformance. The popularity of water-soluble polymers as mobility-control agents in oil recovery processes has increased significantly in recent years. Polymers are applicable to several recovery processes. In addition, because large quantities of chemical are required to flood developed fields, many polymer manufacturers have directed their efforts toward this substantial potential market. Several chemical companies have acquired extensive technology in the manufacture of water-soluble polymers, but most of them lack expertise in the polymers, but most of them lack expertise in the oil-recovery applications of such products. High-molecular-weight polyacrylamides are widely used in secondary and tertiary recovery. The material used in this study was a partially hydrolyzed polyacrylamide marketed by The Dow Chemical Co. as 700 polyacrylamide marketed by The Dow Chemical Co. as 700 series Pusher. Other companies also are developing or marketing polyacrylamides. Polyacrylamides control mobility in reservoirs by increasing the viscosity of injection water and, more importantly, by reducing the formation permeability. Reservoir residence times are long for polymer solutions, since mobility control must be maintained essentially throughout the flood life of these solutions. Therefore, polymer stability under field conditions becomes important. Specifically, conditions that may degrade polymer solutions injected into a reservoir must be determined and evaluated. This paper describes the results of a laboratory study conducted to determine factors affecting the stability of Dow 700 series Pusher. The paper quantitatively describes the effects of several field conditions on the mobility control capability of this polymer, from the standpoint of both viscosity and polymer, from the standpoint of both viscosity and permeability reduction. Guidelines are developed for permeability reduction. Guidelines are developed for handling solutions of this material, including the proper use of treating agents, so as to enhance performance. Dow 500 series Pusher was evaluated in a manner similar to that described here. This polymer, which is also used in oil-recovery applications, is lower in molecular weight than Pusher 700. The behavior of Pusher 500 was very similar to that of Pusher 700 in laboratory experiments, so specific data Pusher 700 in laboratory experiments, so specific data discussed here are limited to the material having a higher molecular weight. In addition to obtaining bench measurements of solution properties, we also measured the effects of polymer degradation on flow behavior by flooding polymer degradation on flow behavior by flooding reservoir cores. Flow studies verified that the effectiveness of polymer solutions in providing mobility control in reservoir rock may be impaired under conditions encountered in the field.

JPT

P. 618