Downhole Hydraulic Control System with Failsafe Piston Design
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Solution Overview
Problem
Existing tubing pressure insensitive control systems for deep set safety valves are complex, costly, and lack simplicity and reliability, as they often require multiple control lines and additional components to ensure fail-safe operation.
Innovation Solution
A simplified control system using a single control line with two discrete piston chambers of differing diameters, connected via a jumper line filled with compressible fluid, which balances hydrostatic pressure and ensures fail-safe closure with fewer moving components and leak paths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple control lines and additional components are used to ensure fail-safe operation, then reliability is improved, but device complexity increases and production cost increases
Solution Approach 1:
The control system is segmented into two discrete piston chambers with opposing pistons that independently respond to control line pressure changes. Each chamber acts as a separate functional unit, allowing the system to maintain fail-safe operation through distributed functionality rather than requiring multiple redundant control lines.
Solution Approach 2:
A compressible fluid serves as an intermediary medium connecting the two piston chambers through a jumper line. This fluid transmits pressure changes between chambers while its compressibility provides a cushioning effect that ensures reliable valve closure even when seal failures occur, eliminating the need for additional control lines.
2Reliability
If multiple control lines are used to offset hydrostatic pressure, then reliability is improved, but ease of operation deteriorates
Solution Approach 1:
Multiple control functions are merged into a single control line system. The opposing pistons work together in tandem, with both chambers receiving control pressure through the same line, thereby simplifying control line management while maintaining fail-safe operation through the coordinated action of the piston pair.
Solution Approach 2:
The opposing pistons are designed with different diameters to create counterbalancing forces that automatically offset hydrostatic pressure effects. The larger piston compensates for the smaller piston's force deficit, creating a self-balancing system that simplifies operation without requiring multiple control lines.
3Device complexity
If fewer moving components and leak paths are used, then device complexity is reduced, but reliability may worsen
Solution Approach 1:
The compressible fluid in the jumper line converts the potential harm of pressure imbalances and seal leaks into a beneficial cushioning effect. When seal failures occur, the compressible fluid absorbs pressure shocks and maintains sufficient force to drive the valve to closure, turning what could be a reliability failure into a protective mechanism.
Solution Approach 2:
The opposing pistons are deliberately designed with asymmetric, different diameters to create unequal surface areas. This asymmetry generates different force magnitudes on each piston, allowing the system to compensate for pressure losses and seal failures while reducing the number of components needed compared to symmetric, equally-sized piston designs.
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 system achieves reliable and cost-effective fail-safe operation with reduced complexity by minimizing the effect of control line hydrostatic pressure, allowing the valve to transition to a closed position efficiently even with seal failures, while maintaining simplicity and reducing production costs.
Implementation Method 1
a jumper line connects the chambers at a point between the seals in each chamber and features a reservoir. The jumper line can be filled with a compressible or other fluid.
Implementation Method 2
The jumper line can be filled with a compressible or other fluid
Implementation Method 3
substantially reduces the effect of control line hydrostatic pressure in a single line with a pair of opposed pistons of differing diameters
Data Source
AI summary
A control system for a subsurface safety valve addresses normal open and closed operation and a failsafe operation if key system components fail. It features a single control line (20) from the surface that splits at the subsurface safety valve and goes to one end of two discrete piston chambers (64, 46) that are aligned and isolated from tubing pressure. The piston (36) in one chamber is larger than in the other and the pistons (36, 52) are connected for tandem movement. Each side of the unbalanced system's piston has a seal mounted to it (38, 54) and another for the rod (40, 56) attached to it that exits the chamber. A jumper line (68) connects the chambers (48,62) at a point between the seals in each chamber and features a large reservoir (70). The jumper line (68) is filled with a compressible fluid. Fail safe closure of the valve occurs if any of the four seals fail.