1. Field of the Invention
The present invention relates generally to devices and seals installed in oil and gas wells for servicing such wells and particularly, but not by way of limitation, to a device and seal for performing fracturing operations on wells.
2. Description of Related Art
In normal operation, a typical oil and gas well may have a production pressure of about 1,500 psi, which is a relatively low pressure. Accordingly, production flow is adequately sealed by a low-pressure tubing head and O-ring seals or compressed rubber seals, or injected plastic seals.
Certain well-servicing operations are performed, however, at higher pressures. In a typical fracturing operation, for example, acids or other fracturing fluids and solids may be pumped into the well at pressures up to 15,000 psi.
Low-pressure tubing heads, conventional O-ring seals and seal retainers are not designed to withstand such high pressures. Therefore, fracturing fluids are likely to leak past conventional O-ring seals, seal retainers and tubing heads.
The leak of fracturing fluids poses an environmental problem. If the acids or other fracturing fluids are not contained, they will enter and contaminate the fresh water zone of the well.
Damage of conventional seals during fracturing operations poses a long term problem resulting in leakage of oil and gas from casing seals. Having leaked past the casing seals, the oil and gas migrates through the casing hangers into the surface pipe and then into shallow water sands.
The leakage of fracturing fluids also causes maintenance problems. The fracturing fluids carry sand and other abrasive material which accelerate wear on valves and other components if allowed to reach those components.