Subsea Riser Surge Protection via Autonomous Valve Extraction
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Solution Overview
Problem
Flexible riser systems in subsea hydrocarbon production are prone to liquid accumulation, leading to unstable liquid flow and potential overfilling of separators, which can cause processing issues and necessitate abandoning the flowline.
Innovation Solution
A system comprising a flexible tubing with autonomous valves arranged along its length, an inlet device at the bottom end, and an optional pressure control system to create a pressure differential, allowing liquid to be extracted from the riser and preventing gas from entering the tubing, thereby mitigating liquid accumulation and surge.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If flexible riser systems are used to transport gas and liquids from well to production facility, then the riser can withstand horizontal and vertical movement due to wave motion, but liquid accumulation occurs in bends or dips leading to liquid surging
Solution Approach 1:
The invention extracts liquid from the riser by introducing a flexible tubing with inlet means that draws liquid out from accumulation zones (sag bends) and transports it to a removal location, thereby preventing liquid surge while maintaining riser flexibility
Solution Approach 2:
The flexible tubing acts as an intermediary element between the riser and the liquid removal system, enabling liquid extraction without compromising the riser's structural flexibility and wave motion accommodation
2Quantity of substance
If liquid accumulates in sag bends of the riser, then liquid may flow towards riser base in unstable manner, but this causes overfilling of separators and processing plant problems
Solution Approach 1:
The invention performs preliminary liquid removal by continuously extracting liquid from sag bends before it can accumulate to surge levels, using a pressure differential created by connecting the tubing to a lower pressure zone to draw liquid out proactively
Solution Approach 2:
The flexible tubing with inlet means extracts liquid directly from accumulation zones in the riser, removing the harmful liquid accumulation before it can cause unstable flow and separator overfilling
3Productivity
If autonomous valves are arranged along flexible tubing to permit liquid passage, then liquid can be extracted from multiple locations, but device complexity increases
Solution Approach 1:
The autonomous valves along the flexible tubing self-regulate liquid passage based on local pressure conditions, enabling multi-location extraction without requiring complex external control systems, thus improving productivity while limiting complexity increase
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
Effectively reduces the risk of liquid surging by extracting accumulated liquids from the riser, maintaining stable fluid flow, and preventing overfilling of separators, thus ensuring continuous operation of the processing plant.
Implementation Method 1
The system may further comprise a pressure control system arranged to create a pressure differential between the riser and the flexible tubing
Implementation Method 2
The system may further comprise a spacer or a weight arranged to urge the inlet device against the bottom wall of the riser
Data Source
AI summary
A system for liquid surge protection of a subsea riser having a horizontal portion on the seabed and a sag bend portion includes: a flexible tubing having a top end and a bottom end; a plurality of autonomous valves configured to permit liquid to pass through into the flexible tubing, wherein the autonomous valves are arranged between the top end and the bottom end of the tubing; and an inlet device coupled to the bottom end of the flexible tubing, wherein said inlet device is biased against a bottom wall the riser.