Design Methodology for Swellable Elastomer Packers (SEPs) in Fracturing Operations

Abstract

Abstract During past 7 years, swellable elastomer technology has been introduced to the oilfield, and its acceptance has been so rapid that its scope of application has rapidly expanded. Swellable technology employs the principle of elastomeric expansion in hydrocarbon or water to form a permanent seal. With the increasing acceptance of this concept for the oilfield, new applications are being explored, and this paper will discuss the application of swellable elastomer packers (SEPs) in stimulation operations. These applications include acid stimulations and/or hydraulic fracturing operations. During stimulation operations, SEPs are 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:The downhole conditions; i.e., 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; i.e., the forces that occur from the shrinkage of the pipe during the treatment that subject the SEPs to additional forces that do not occur in conventional zonal-isolation applications.Thermal contraction of the sealing element; i.e., the contraction that occurs due to the injection of the stimulation fluids that will cause the temperature of the packer to drop. This phenomenon causes the sealing element to partially contract and will result in altered sealing properties, and ultimately, the loss of the pressure seal. This paper describes the technical challenges and discusses resulting design methodology based on modeling (downhole parameters, anchoring forces) and laboratory testing (thermal contraction measurements) that have been developed to resolve these issues. This design methodology is not limited to stimulation applications but is applicable to any scenario with dynamic loads on SEP applications such as in water injection wells, etc. Finally, case histories are provided to illustrate the successes that have been achieved using the design methodology described. Introduction It has been approximately 7 years since swellable technology was introduced to the oil and gas industry, and since its introduction, many changes in the technology have taken place. Initially, the main application was the development of swellable elements for packers.1–7 These swellable elastomer packers were designed to provide zonal isolation in an openhole environment. As the technology became more and more accepted, and operators gained confidence in the capabilities of the technology itself and in running SEPs in wells, other applications were explored. The initial applications allowed operators to design wells with openhole completions, allowing for simpler operations (cementing and perforating were no longer needed) and higher production.