Delaying Gelation of Aqueous Polymers at Elevated Temperatures Using Novel Organic Crosslinkers
Authors: Dovan H.T. , Hutchins R.D. , Sandiford B.B. 
Published: December 2007

Abstract
This paper presents novel organic crosslinkers that extend the temperature limitations of currently available polymer gel systems. These organic crosslinkers have application in steam injection, geothermal and high temperature oil and gas wells. One crosslinker exhibits a gelation time of several days at 350 F. Long-term stability has been verified for at least one year at 300 F. Some novel organic crosslinkers for low and medium temperature applications are also presented.

Introduction
Polymer gels have been applied in oil and gas wells for many years to control the flow of fluids within the reservoir. They are inexpensive, simple to apply, versatile in their application and readily available. One major limitation of some gel systems currently in use is that the gelation reactions cannot be delayed for more than several minutes at elevated temperatures. When retardants are used to alleviate this problem, the gel typically weakens and loses some of its gel strength or becomes completely unstable.

High Temperature Uses for Gels
Several of the organic crosslinkers presented in this paper have application in steam injection wells, geothermal wells and in oil and gas wells where high reservoir temperatures have historically limited the use of polymer gels.
Steam Injectors. Steam injection is beneficial to the production of oil in many reservoirs and in particular, to heavy oil reservoirs, by reducing oil viscosities and removing tarry and paraffin deposits. However, due to heterogeneity and to the fact that steam rises to the top of injected zones because of its low density, steam channels can develop leaving potentially productive intervals unswept.
Polymer gels and foaming agents have been used to reduce flow through these channels. The temperature in these steam channels can be as high as 500 F which increases the difficulty in forming an in-depth stable foam or gel. Geothermal Wells. Steam and hot water production from geothermal wells are economical sources of energy for the generation of electricity. This production is often accompanied by high concentrations of salts and undesirable gases. Condensate is generally re-injected into the geothermal reservoir and can sometimes detrimentally affect nearby producing well temperatures.
Temperatures in these wells could be as high as 600 F. At this time, we do not have a time-delayed gel for these extreme temperatures; however, successful treatments should be possible below 400 F.
High Temperature Oil and Gas Wells. Low temperature reservoirs have been successfully treated with current polymer gel technology. However, there is a need to extend these gel treatments to higher temperature formations because of the increasing depths of commercially productive reservoirs. Temperatures of some oil and gas bearing reservoirs can exceed 400 F. Most reservoirs have problems with channeling during primary and enhanced production, but in higher temperature reservoirs, the problem is more difficult to solve by the use of polymer gel treatments. Polymer instability, rapid gelation and improper placement can result in treatment failures.