Subsea Riser System with Lowered Workover Package
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Solution Overview
Problem
Conventional riser systems face challenges in maintaining tension and safety during subsea operations, particularly with telescopic joints that handle high pressures, which can be hazardous due to the exposure of well fluids at high pressures on the vessel deck, posing risks to personnel and compromising health, security, and environmental safety.
Innovation Solution
A riser system with an upper workover riser package (UWRP) arranged below the tension means connection, featuring main sealing elements and latching means for equipment interchange, along with slip joints that allow for angular deviation and flexible movement to compensate for vessel movements, ensuring constant tension and safe operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the SBOP is located on top of the riser string above the telescopic joint, then the riser can be controlled and sealed, but high-pressure well fluids are exposed on the vessel deck creating safety hazards
Solution Approach 1:
The patent inverts the conventional arrangement by positioning the UWRP with BOP equipment below the telescopic joint instead of above it. This inversion keeps high-pressure well fluids contained below deck level while maintaining sealing and control capabilities, thereby eliminating safety hazards to personnel on the vessel deck.
Solution Approach 2:
The telescopic joint acts as an intermediary element between the UWRP and the vessel deck. It provides a mechanical connection that accommodates vertical movements while maintaining the sealed connection, allowing the BOP to remain below deck while still controlling the riser effectively.
2Ease of operation
If telescopic joints are used to accommodate vessel movement, then heave compensation is achieved, but maintaining seals under high pressure becomes difficult
Solution Approach 1:
The telescopic joint is designed with dynamic sealing capabilities that accommodate vertical movement between the vessel and subsea wellhead. The joint can extend and retract to maintain tension on the riser while sealed connections prevent pressure leakage during heave compensation operations.
Solution Approach 2:
The patent employs replaceable seal elements within the telescopic joint and UWRP that can be exchanged during maintenance operations. This allows the system to maintain reliable sealing performance over time by replacing worn seals rather than replacing entire components.
3Ease of operation
If the riser is depressurized for wire line or coiled tubing operations, then equipment can be inserted, but tension control becomes more complex with telescopic elements
Solution Approach 1:
The riser system is segmented into distinct functional zones: the UWRP section for equipment insertion and control, the telescopic joint section for heave compensation, and the riser string for fluid transport. This segmentation allows independent optimization of each section, simplifying tension control during depressurized operations.
Solution Approach 2:
The telescopic joint incorporates automatic tension maintenance mechanisms that adjust the joint extension automatically in response to vessel movement, reducing the need for complex active control systems during equipment insertion operations.
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 maintains constant tension in the riser, enhances safety by keeping high-pressure systems below the rig floor, and allows for efficient interchange of workover equipment, thereby improving health, security, and environmental safety during subsea operations.
Implementation Method 1
These tension means are connected to the riser in one section of the riser and also connected to the vessel, to actively compensate for vertical movement variations between the vessel and the seabed to keep a mainly constant tension in the riser
Implementation Method 2
The slip joints that allow for angular deviation and flexible movement to compensate for vessel movements
Implementation Method 3
The UWRP can thereby be kept in tension together with the riser. The UWRP will in normal manner comprise a first main sealing element and a second main sealing element
Data Source
AI summary
The present invention regards a riser system comprising at least one riser extending from a subsea wellhead to a surface vessel, tension means for keeping the at least one riser tensioned, which tension means are connected to the vessel, a upper workover riser package (UWRP) located at the upper section of the riser and arranged to seal off the riser passage.According to the invention the UWRP is located below the connection point of the tension means to the vessel, giving the UWRP a position stationary relative a seabed, and that the UWRP comprises an interface adapted for the connection of different kinds of workover equipment. The invention also regards a method for inserting tools into a riser.