Subsea Test Tree Valve Actuation After Control Line Shear
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Solution Overview
Problem
In the oil and gas exploration and production industry, the actuation of BOP shear rams can sever control lines to subsea test tree (SSTT) valves, preventing them from closing and compromising pressure control, especially during emergency shutdowns, due to insufficient spring force and lack of redundancy in control systems.
Innovation Solution
A subsea test tree assembly with a control system that automatically moves the SSTT valve to a closed position upon detecting sheared control lines, using a pilot line and hydraulic accumulator to ensure the valve closes even after control line severance, thereby maintaining pressure control and redundancy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If BOP shear rams are actuated to sever control lines during emergency shutdown, then the control lines are cut and isolated, but the SSTT valve cannot receive hydraulic fluid and fails to close, compromising pressure control
Solution Approach 1:
The patent applies preliminary action by pre-positioning a hydraulic accumulator connected to the SSTT valve before control line severance. The accumulator is charged with hydraulic fluid in advance and automatically discharges upon detection of control line failure, enabling the valve to close without requiring active control lines at the moment of emergency shutdown. This preliminary preparation ensures the valve can actuate independently when control lines are severed by BOP shear rams.
Solution Approach 2:
The patent introduces a hydraulic accumulator as an intermediary energy storage device between the hydraulic fluid source and the SSTT valve. This intermediary component decouples the valve actuation from the control lines, allowing the valve to receive hydraulic fluid through an alternative path (the accumulator) when control lines are severed. The accumulator acts as a mediator that transfers hydraulic energy independently of the severed control lines, ensuring reliable valve closure during emergency shutdown.
2Reliability
If spring force is used to close the SSTT valve, then the valve can close without hydraulic fluid, but the spring force is insufficient to sever tubing or equipment extending through the valve
Solution Approach 1:
The patent merges two distinct mechanisms into a single integrated valve actuation system: a spring mechanism for closing the valve and a hydraulic accumulator for providing cutting force. The spring is configured to automatically close the valve when hydraulic pressure is lost, while the hydraulic accumulator, connected to the same valve, can deliver high-force hydraulic pressure to drive the valve ball against tubing for severing. This combination allows the valve to perform both sealing and cutting functions through a single integrated design, resolving the contradiction between insufficient spring force and the need for cutting capability.
3Device complexity
If control lines are severed by BOP shear rams, then the control system loses redundancy, but the SSTT valve remains unable to actuate without hydraulic fluid supply
Solution Approach 1:
The patent implements self-service by designing the SSTT valve system to automatically activate without requiring external control signals after control line severance. The hydraulic accumulator is configured to automatically discharge its stored hydraulic fluid when control line pressure is lost, enabling the valve to actuate autonomously. Additionally, the spring mechanism provides automatic valve closure without requiring active control input. This self-service capability ensures the valve can actuate independently when the control system loses redundancy due to severed control lines, eliminating the need for complex active control during emergency shutdown.
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
Ensures the SSTT valve can be actuated to close and maintain pressure control even after control line severance, preventing blockages and ensuring safe shutdown procedures by using a pilot line and hydraulic accumulator to provide the necessary force and redundancy.
Implementation Method 1
using a pilot line and hydraulic accumulator to ensure the valve closes even after control line severance
Implementation Method 2
using a pilot line and hydraulic accumulator to provide the necessary force and redundancy
Implementation Method 3
the control system comprises a pilot line, shearing of the pilot line triggering movement of the valve to the closed position
Data Source
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AI summary
A subsea test tree assembly (40) is disclosed which comprises at least one subsea test tree or SSTT (70, 72), the SSTT comprising a valve (74, 76) having at least one of a cutting function and a sealing function, the valve being movable between an open position and a closed position via hydraulic fluid supplied to the valve through control lines (78, 80; 82, 84); and a control system (86) comprising a source of hydraulic fluid (88), the control system being arranged to supply hydraulic fluid from the source of hydraulic fluid to the valve of the at least one SSTT on detecting that the control lines have been sheared, to automatically move the valve to the closed position. A method of controlling a well using an SSTT assembly is also disclosed.