wellhead component expansion and contraction, and casing growing. Based on different well condition, SAGD Wellhead or CSS wellhead can designed to have one, two or combined the wellhead systems of the following:
- Steam Injection Thermal Wellhead System: As the name implies, it receives high temperature steam to be injected into well formation. This term is usually used in SAGD wellhead system. CSS wellhead usually have one wellhead system for both steam injection and oil production.
- Steam Production Thermal Wellhead System: As the name implies, it is an oil production wellhead. This term is usually used in SAGD wellhead.
- Thermal ESP Wellhead: Designed to accept and seal a specially engineered electric feed through connector which carrying high voltage, high amperage power to an electric submersible pump (ESP) at the base of the production tubing. It becomes popular this days in SAGD application.
- Thermal Reciprocating Rod Pump Wellhead System: This lift system includes a Pumpjack, a polished rod and a downhole pump. The Polished Rod is reciprocated vertically to activate the pump and bring the oil up to surface. The wellhead design must include a thermal stuffing box and blowout preventer (BOP).
- Thermal PCP Wellhead System: The progressing cavity pump (PCP) drivehead and stuffing box are mounted above the flow cross of wellhead. The rod does not reciprocate like Rod Pump, instead the rod is rotating to drive the downhole pump. Therefore, the PCP wellhead design must consider the additional weight of the motor or drivehead and sustain the vibration, torque, and fatigue created by the PCP operation.
- Thermal Gas Lift Wellhead System: Designed to accept injecting gas through the tubing-casing annulus. Injected gas can reduce the oil density and assist the lift of the oil column out of the wellbore.
- Thermal Observation Wellhead System: As the name implies, this wellhead is used in Observation Well which monitor formation conditions or the efficiency of the reservoir depletion process. Depending on their function, observation wells may be designed as a simple threaded wellhead for anticipated low pressure and non-perforated well.
Thermal recovery techniques are commercially and matured developed for oil sand (or bitumen) in Alberta Canada. The techniques inject high temperature steam into formation to reduce the viscosity of bitumen or heavy oil so that it can flow in the wellbore. The popular thermal wellhead designs are steam-assisted gravity drainage wellhead (SAGD wellhead) or cyclic steam stimulation (CSS wellhead). The design must consider the high temperature effects on seal material,
API 6A Thermal Wellhead Design