Subsea Test Tree Ball Actuation for Low-Pressure Reopening
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Solution Overview
Problem
Subsea safety trees face challenges in reopening after emergency closure due to loss of control lines, requiring elevated pressure that can be near operational limits, making it undesirable and potentially unsafe.
Innovation Solution
A valve mechanism using a first piston for closing and shearing a workstring, and a second piston for sealing, allowing reopening at lower pressures, reducing stress and enabling a safer operational method.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single piston mechanism is used for valve closure and shearing, then the valve can be closed and workstring sheared, but reopening requires elevated pressure near operational limits which is unsafe
Solution Approach 1:
The valve actuator is segmented into two separate pistons: a first piston dedicated to closing and shearing the workstring, and a second piston dedicated to sealing the valve. This segmentation allows each piston to be optimized for its specific function and enables reopening to be achieved by the second piston at lower pressures, eliminating the safety concerns associated with using high pressures near operational limits
2Ease of operation
If elevated pressure is used to reopen the valve after emergency closure, then the valve can be reopened, but the stress on the system increases making the operation potentially unsafe
Solution Approach 1:
By segmenting the valve actuator into two specialized pistons, the system can reopen the valve using only the second piston at low pressures, eliminating the need to apply elevated pressures that create stress and safety risks
Solution Approach 2:
The second piston acts as an intermediary mechanism that enables valve reopening through a different physical pathway than the first piston. This intermediary mechanism uses low pressure to achieve the reopening function that would otherwise require high pressure, thereby eliminating harmful stress effects
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
Enables the subsea test tree to reopen at significantly lower pressures than typical operational limits, reducing stress and improving safety and robustness of the operation.
Implementation Method 1
a gas charge within an activation chamber to apply a biasing force to a main piston
Implementation Method 2
The main piston can be contacted by the ball support to shear a workstring within the ball passage
Implementation Method 3
control piston configured to translate the ball support into the open position in response to a predetermined volume of fluid delivered through a conduit
Data Source
AI summary
A method of actuating a subsea tree comprising opening a valve assembly by transferring a first volume of fluid into a first chamber and closing the valve assembly from the open position to a shear position via a gas charged valve actuator in response to the transfer of fluid out of the first chamber. Shearing a workstring positioned within an axial bore of the valve assembly with the valve via the gas charged valve actuator. Closing the valve from the shear position to a closed position with one or more gas charged push rods to isolate the wellbore above from the wellbore below the closed valve. The shearing force generated from the gas charged valve actuator is greater than the closing force of the one or more push rods.