Subsurface Safety Valve Equalization for Flapper Pressure Relief
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Solution Overview
Problem
Conventional subsurface safety valves face difficulties in reliably opening due to significant pressure differentials across the flapper valve, which can cause damage and make it hard to overcome the force required for opening, especially when well fluid pressure acts on a large surface area.
Innovation Solution
The implementation of an equalizing mechanism that allows pressure above and below the flapper to equalize prior to complete opening, using various designs such as ball and spring mechanisms, plungers with radial projections, and elastomeric seals to facilitate fluid flow and resist debris, ensuring the valve can open effectively without damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If control fluid pressure is increased to overcome the pressure differential across the flapper valve, then the valve can be opened, but the force required may cause damage to the sleeve, flapper valve, or pivot mounting
Solution Approach 1:
The invention divides the pressure differential problem into two separate stages: first equalizing the pressure across the flapper using the equalizing piston and annular passage, then opening the valve using the control piston. This segmentation allows the opening force to be applied only to overcome the spring bias rather than the full pressure differential, preventing structural damage.
Solution Approach 2:
The equalizing piston acts as an intermediary mechanism between the control fluid pressure and the flapper valve. It first equalizes the pressure across the flapper through the annular passage, reducing the pressure differential before the control piston applies force to open the valve, thereby preventing direct transmission of excessive force to the structural components.
2Force
If the cross-sectional area of the opening piston is increased to provide sufficient force, then the valve can be opened, but the fluid pressure required may burst the control line carrying hydraulic fluid
Solution Approach 1:
The opening process is segmented into two phases: pressure equalization (reducing the pressure differential) and valve opening (overcoming spring bias only). This allows the control piston to operate at lower pressure after equalization, preventing control line bursting while still providing sufficient opening force.
Solution Approach 2:
The equalizing piston performs a preliminary action by equalizing the pressure across the flapper valve before the control piston attempts to open it. This preliminary pressure equalization reduces the force requirement for the control piston, allowing smaller piston area and lower control line pressure.
3Reliability
If well fluid pressure acts on a large surface area of the closed flapper, then the valve remains sealed, but opening of the flapper becomes difficult
Solution Approach 1:
The valve operation is segmented into sealing phase (where full pressure differential maintains seal) and opening phase (where equalized pressure makes opening easy). The equalizing piston enables this segmentation by first balancing the pressure while the valve remains sealed, then allowing easy opening.
Solution Approach 2:
The equalizing piston serves as a mediator that temporarily balances the pressure across the sealed flapper without requiring it to open. This intermediary pressure equalization maintains sealing effectiveness while removing the difficulty of opening, as the control piston only needs to overcome spring bias afterward.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The equalizing mechanism ensures reliable and safe operation of the subsurface safety valve by reducing the pressure differential, preventing damage and ensuring the valve can open and close effectively, even under high pressure conditions, thus preventing uncontrolled fluid flow.
Implementation Method 1
an equalizing device located at least partially within the equalization fluid flow passageway. The equalizing device, when in a closed position, restricts the flow of fluid through the equalization fluid flow passageway. The equalizing device enables the pressure above and below the valve member to equalize prior to the complete opening of the valve member.
Implementation Method 2
The equalizing device biased to a closed position
Data Source
AI summary
A subsurface safety valve for controlling fluid flow in a well conduit incorporating a pressure equalizing feature. The safety valve includes a body member having a longitudinal bore, a valve actuator having axial movement within the longitudinal bore and a valve that restricts flow through the longitudinal bore. An equalization fluid flow passageway provides a fluid path between the longitudinal bore above the valve and the longitudinal bore below the valve. An equalizing device is located within the equalization fluid flow passageway and configured to resist sand and debris effects on its operation, the equalizing device regulating flow through the equalization fluid flow passageway and operated by the valve actuator prior to opening the valve.