In the oil and gas industry, one or more casings or pipes are placed into the well bore. In addition to production pipe, which is used to extract hydrocarbons from the well, a well liner and various casings are optionally present. For example, a conductor casing, may be installed to prevent the top of the well from caving in and aid in the process of circulating the drilling fluid up from the bottom of the well. A surface casing may also be present. The surface casing fits into the top of the conductor casing and extends a few hundred feet to a few thousand feet into the well. The surface casing protects fresh water deposits near the surface of the well from being contaminated by leaking hydrocarbons or salt water from deeper in the ground. Intermediate casings or liner strings are placed to mitigate hazards caused by abnormal underground pressure zones, underground shale, and formations that might otherwise contaminate the well, such as salt water deposits.
In addition, a wellhead is used to prevent oil and natural gas leaking out of the well and to prevent blowouts. It is mounted at the well opening and is used to manage the extraction of hydrocarbons from the well. The well head generally includes a casing head, tubing head and a christmas tree. The casing head includes heavy fittings and supports the length of the casing that is run into the well and includes seals between the fittings and the casing. The tubing head provides a seal between the production pipe and the surface. The tubing head also supports the length of production pipe and provide connections at the surface which allow the flow of the fluids out of the well to be controlled. The christmas tree fits on top of the casing head and tubing head and contains tubes and valve that control the flow of hydrocarbons and other fluids out of the well.
Various seals may be positioned within the well between the casings and production pipe, between the casings and casing head, and the production pipe and tubing head. Standard seals (e.g., non-swellable o-rings) or swellable seals (e.g., swellable o-rings, swelling packing elements, etc) generally do not perform well in damaged bores and/or in gas applications.