Completion Equipment
The primary function of the Christmas Tree and wellhead is to provide a safe and secure path for produced hydrocarbons out of the well into production facilities. The master, swab, and flow line valves provide means to shut in the well when needed. Some master valves provide wireline cutting capability.
The tubing hanger provide isolation between the tubing string and the annulus. The Surface Safety Valve (SSV) will be on a circuit that allows for automatic shut-in in the event of an emergency.
A Surface-Controlled Sub-Surface Safety Valve (SCSSV) is required in most locations. These valves are held open by hydraulic pressure on a control line. If something happens to the control line pressure, the SCSSV will automatically close.
Actuated valves, which can be either hydraulically or pneumatically controlled, are required on all offshore areas in the US. They may also be required on some inland water and land locations
The Tree Test Plug is installed in the tubing hanger profile with a surface lubricator, polished rod and setting tool. It is designed to hold pressure from above. The plug is easily pulled with a pulling tool that allows pressure equalization across the plug.
The Back Pressure Valve, installed like the Test Plug, is designed to hold from below, and can be pumped through if necessary. It is pulled in a similar fashion as the Test Plug.
The tubing hanger serves as surface
anchor for the production string and while doing so it isolates the casing from the tubing in the wellhead. The hanger serves as a receptacle for a back pressure valve and as a termination point for control lines for downhole safety valves
This style of BPV Lubricator incorporates hydraulics to set and pull back pressure valves.
Various cross-overs or tree connections are available to make it adaptable to most tubing sizes and trees.
The hydraulic unit can be placed some distance away from the tree allowing the unit to be operated remotely for added safety.
Ring gaskets are placed in the ring grooves of flanges. Below are four of the most common types of ring gaskets. In all cases, the rings are designed to seal metal-to- metal, so, no teflon tape is to be used, don’t grease the grooves or gaskets, and clean the ring grooves with soap and water, not a solvent that may leave a film. Additionally, when a flange is “broken” and then made back up, a new gasket should be used.
API type, non-energized by internal pressure. Sealing takes place along small bands of contact between the groove and the gasket. Does not allow flange face-to-face contact so periodic tightening of the flange is recommended.
Subsurface Safety Valve
A subsurface safety valve is essentially a shutdown valve installed at the upper wellbore for emergency shutdown in the event of damage to the surface facilities. This is to avoid releasing reservoir fluids to the environment at the surface.
This makes SSSV a very important component of a well completion. Hence such a safety valve needs to be fail safe in order to isolate well bore in any kind of system failure or damage to surface production, control and safety facilities.
The subsurface safety valve is also part of the system and will close automatically when hydraulic supply pressure is bled from the safety valve. The valve must be positioned below the surface, at a distance that will isolate it from catastrophic damage to the surface facilities. This is often called the “cratering depth.”
Tubing Retrievable Remotely Controlled Safety Valve
Subsurface safety valves are installed in the production string for the purpose of shutting off well flow in the event of an emergency.
All safety valves fall into one of two categories: remote controlled or direct controlled. The diagram at right depicts a remotely controlled valve. These valves are normally closed, being held in the closed position by an internal spring.
They can be installed as an integral part of the tubing string but can be serviced, to a limited extent, by wireline. Safety valves can also be installed in tubing nipples and serviced entirely by slickline. The most common style is remotely controlled and hydraulically operated.
The valves, which may be called upon to open under extreme differential pressure, have an equalizing feature when hydraulic opening pressure is applied. After equalization is accomplished the valve is fully opened.
