New Generation Inflatable Packing Elements (1991)

ABSTRACT Recent technological improvements in inflatable packing elements has enabled inflatable packers to exhibit far superior performance characteristics in comparison to previous designs, thus expanding conventional and non-conventional applications. This paper describes the development, analysis and testing of a new generation inflatable packing element. It discusses an elastomer development program that was initiated to formulate new compounds with improved physical properties, including higher elongations, increased strength at elevated temperature and compatibility with various downhole fluids. This paper also discusses test procedures used to simulate downhole conditions in order to evaluate overall performance of various elements. The overall performance of inflatable packers is evaluated in terms of how far the element can expand and their corresponding pressure strength. The authors have been instrumental in the development of this technology and with its subsequent successful application in Prudhoe Bay, the North Sea and in the Gulf of Mexico. The authors will discuss how the technology, once developed, was transferred to enhance the overall performance of other inflatable products. Customer-specific applications along with field test data are also discussed. INTRODUCTION Inflatable tools have long been valued in completion and workover operations due to their unique ability to expand to several times their diameter and to seal effectively. Past drawbacks to inflatable systems has been their expansion limitations at higher temperatures and their differential pressure capacities. Inflatable element technology was improved considerably in the early 1980's with the introduction of the "rib" type element. This element is constructed using thin metal strips which are layered between the rubber sealing cover and the inner tube within. These ribs are overlapped and provide extrusion protection for the inner tube upon inflation of the element. The rib design replaced previously used reinforcing methods, which severely restricted the elements expansion limits. The new rib design allows much greater expansion and still maintains the reinforcement required for the inner tube. The rib design also provides an improved element-to-casing anchor which dramatically increases the differential pressure required to make the tools slide once set. This type of element is designed in single anchor, double anchor and full cover versions, which are used for the varying applications required of these tools. The anchoring feature is obtained by having exposed ribs not covered by the outer elastomer sealing cover. When the element is inflated, these ribs are forced against the casing wall providing a friction anchor. A single anchor element has a section of exposed ribs on only one end of the sealing cover, whereas, a double anchor has exposed ribs on both ends. The single anchor design is used if pressure differentials are being applied from only one direction, as with most packer stimulation jobs. The double anchor design is used for bridge plug applications where pressure differentials could be applied to both sides of the tool. A full cover element is used when setting in open hole and does not have any exposed ribs which may be damaged when setting in irregular open hole profiles.