Use of Crosslinked Polymers in High-Density Brines

This paper discusses the use of crosslinked polymers as a fluid-loss-control method in high-density brines, 15.0 lb/gal and higher. The ability to control fluid loss in brines of this density is extremely important to the operator because of the high cost of these brines. Historically, crosslinked polymers designed for heavy brines were not an option because when mixed in heavy calcium bromide (CaBr2) and zinc bromide (ZnBr2) brines, the temperature limitation was typically lower than 225°F. Additionally, most operators spot losscontrol pills of a higher density than the wellbore brine so that the pills remain in place when spotted. However, specific case histories show that using a lighter-weight lost-circulation pill designed with a 14.2-lb/gal calcium bromide in wellbore brines up to 17.5 lb/gal is not only successful, but it uses polymers that are much more temperature stable. The crosslinking polymers used in the 14.2-lb/gal calcium bromide do not yield in highdensity calcium bromide and zinc bromide fluids, and their temperature limit is 350°F. This paper documents three specific cases that clearly demonstrate that fluidloss-control pills lighter than wellbore brines can be used successfully. The results of an investigation addressing why these specific applications worked is also presented. The results demonstrate how crosslinked gels that can float in heavier brines are able to remain in place and accomplish the task of stopping fluid loss even though the gels may be subject to flotation in heavier wellbore brines.