| abstract |
A seal for use in high temperature, aggressive environments, such as a geothermal well, including a ring-shaped element of a polymer, such as tetrafluoroethylene/perfluoro (alkyl vinyl ether) copolymer, which is substantially crystalline at room temperature, has a crystalline melt temperature above 500° F., and melts at a temperature above 650° F. The polymer has a molecular weight of at least about 400,000 and is characterized by molecular chain entanglements to the extent of an average of at least about ten physical entanglements per chain when the polymer is in an amorphous state. The polymer element expands in response to the high temperatures within the well, so that when the seal is located in the annular space between concentric tubular well members, it expands to press tightly against both members. The polymer element is an initially flat ring formed by heat and pressure into a non-flat ring shape, whereby upon being heated by the well temperature the element tends to return to its initial shape. The seal includes a ring-shaped back-up member contacting one face of the polymer element, the back-up member being formed of a mesh of knitted metal wire. |