Modified Casing Coupling Pressure Relief Valve for Subsea Wells
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Solution Overview
Problem
Subsea oil and gas wells are vulnerable to annular pressure buildup due to sealed annuli in subsea wellheads, which can lead to catastrophic failures such as inner or outer casing collapse or rupture, as existing pressure relief solutions are either unreliable or difficult to install and calibrate.
Innovation Solution
A modified casing coupling with a pressure relief valve that includes a through bore with a ball seat and sealing ball, where the tensioning element, such as a coil spring or Belleville spring washer, allows the ball to release trapped annular pressure at a predetermined level, ensuring the valve opens before the inner string collapses or the outer string bursts, and can be easily installed and serviced.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a milled thin wall section is created in the outer string casing to relieve pressure, then pressure relief is achieved, but the wall strength is compromised and unpredictable failure pressure occurs
Solution Approach 1:
The pressure relief function is segmented from the casing wall itself and placed in a separate receptacle housing the burst disk assembly. This allows the casing to maintain its full structural integrity while the separate receptacle handles the pressure relief function through the burst disk mechanism.
Solution Approach 2:
A receptacle acts as an intermediary component between the sealed annulus and the casing wall. The receptacle houses the burst disk assembly which serves as a mediator to relieve pressure before it can compromise the casing wall strength, thus protecting the primary structural element.
2Reliability
If subsea wellhead installations seal all casing annuli to prevent fluid leakage, then well integrity is improved, but pressure buildup cannot be bled off and catastrophic failure risk increases
Solution Approach 1:
The burst disk assembly is pre-installed in the receptacle during well construction, before production begins. This preliminary action ensures that the pressure relief mechanism is already in place and ready to function automatically when pressure buildup occurs during production, maintaining both well integrity and pressure management.
Solution Approach 2:
The burst disk assembly provides self-service pressure relief by automatically failing at a predetermined pressure without requiring external intervention. The system monitors and relieves pressure autonomously through the burst disk mechanism, maintaining well integrity while preventing catastrophic failure from pressure buildup.
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 solution provides reliable and cost-effective pressure relief, preventing damage to the well casing by releasing pressure at a predetermined level, ensuring the integrity of both inner and outer casings, and is adaptable for both internal and external pressure scenarios.
Implementation Method 1
a tensioning element, such as a coil spring or Belleville spring washer
Implementation Method 2
releasing pressure at a predetermined level
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
A modified casing coupling houses a pressure relief valve body having a through bore with opposing end openings. The through bore communicates with the interior of the modified casing coupling at one end opening thereof and with an area surrounding the modified casing coupling at an opposite end opening. The through bore includes a ball seat adjacent one end opening thereof which receives a sealing ball. The ball is urged in the direction of the ball seat by a tensioning element. The ball is exposed to annular pressure trapped between successive lengths of well casing located in the well borehole. The amount of tension exerted on the ball by the tensioning element is selected to allow the ball to move off the ball seat to release trapped annular pressure between the selected casing strings once a certain annulus pressure is reached.