Designing Swellable-Elastomer Packers in Fracturing Operations

Abstract

This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper OTC 20157, "Design Methodology for Swellable-Elastomer Packers in Fracturing Operations," by Rutger Evers, SPE, Dustin Young, SPE, Greg Vargus, SPE, and Kristian Solhaug, SPE, Halliburton, prepared for the 2009 Offshore Technology Conference, Houston, 4–7 May. The paper has not been peer reviewed. The value of swellable-elastomer technology is its ability to form a permanent seal by elastomeric expansion in hydrocarbon or water. One application is swellable-elastomer packers (SEPs) in acid-stimulation and hydraulic-fracturing operations. The design process included modeling of down-hole parameters and anchoring forces. Laboratory testing included thermal-contraction measurements developed to resolve technical challenges for stimulation operations. Introduction The initial application of swellable elastomer was swellable elements for packers designed to provide zonal isolation in an openhole environment. Now, swellable elastomers are used in many applications. A recent application is in stimulation operations, in which SEPs were subjected to a very specific set of conditions that significantly affect the sealing performance of the tool(s). Three primary challenges must be addressed when designing SEPs for stimulation applications.Downhole conditions—the main parameters to which the tool will be subjected, such as the downhole pressure and the average temperature of the sealing elements.Anchoring forces—forces from the shrinkage of the pipe during the treatment that, in turn, subjects the SEPs to additional forces that do not occur in conventional zonal-isolation applications.Thermal contraction of the sealing element—contraction resulting from injection of stimulation fluids that will reduce the temperature of the packer. This phenomenon causes partial loss of contact of the sealing element and results in altered sealing properties. Ultimately, pressure-seal loss can occur. Hydraulic Fracturing and SEPs One area of research and development is in hydraulic fracturing, and by combining multidisciplinary fields of expertise, reliable designs have been developed. Pump rates and volumes of fluids pumped usually are high and can be from 40 to 90 bbl/min. With such high rates, the fluids will remain cool while being pumped downhole, resulting in a cooling effect of the fluid on the tubing side of the packer. Design Two parameters, temperature and pres-sure, have a major role in designing an SEP, especially for stimulation operations. Pressure has always been a main parameter for SEP design, but for stimulations, the temperature effect on the differential pressure (DP) across the SEP must be taken into account.