Riser Segmentation for Multiphase Slug Suppression
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Solution Overview
Problem
Riser slugging in multiphase pipelines, characterized by alternating liquid and gas flows, poses challenges in fluid extraction from subsea wells, particularly at low pressures, leading to reduced production and premature well abandonment due to cyclical surges and back-pressure issues.
Innovation Solution
A system comprising a pipe with a liquid flow path and level measuring means inside the riser, allowing for controlled gas and liquid separation and flow adjustment, eliminating back-pressure and suppressing riser slugs by regulating the liquid column position using differential pressure and control mechanisms.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the flow rate in the multiphase pipeline is increased to prevent riser slugging, then the slugging phenomenon is suppressed, but the pressure drop over the pipeline increases requiring increased pressure from pumps or compressors
Solution Approach 1:
The riser is divided into multiple sections with intermediate gas outlets positioned at different heights. This segmentation allows gas to be discharged at multiple levels rather than accumulating at the top, preventing the formation of large gas pockets that cause slugging. The segmentation principle resolves the contradiction by maintaining lower flow rates while suppressing slugging through distributed gas removal.
Solution Approach 2:
Intermediate gas outlets act as intermediary structures between the liquid discharge point and the top of the riser. These outlets serve as mediators that continuously remove gas from the liquid stream at multiple levels, preventing gas accumulation and back-pressure buildup. This intermediary approach allows the system to operate at lower flow rates without experiencing severe slugging.
2Reliability
If throttling of the outlet from the pipeline is used to handle slugging, then transient and terrain slugging can be managed, but regular riser slugging continues to occur and production is reduced
Solution Approach 1:
The riser is segmented with multiple intermediate gas outlets positioned at different heights along the riser. This segmentation continuously removes gas from the liquid stream at multiple levels, preventing gas accumulation and the formation of slug flows. By maintaining continuous gas discharge throughout the riser, the system preserves steady fluid flow and maximizes production while handling all types of slugging including regular riser slugging.
3Reliability
If a control valve is used to choke the flow and prevent slug flow, then slug flow can be controlled, but the system complexity increases and steady flow is not maintained
Solution Approach 1:
Instead of using a single complex control valve system, the invention segments the riser into multiple sections with intermediate gas outlets positioned at different heights. This segmentation provides multiple simple discharge points for gas throughout the riser, eliminating the need for complex active control mechanisms. The segmented structure maintains steady flow by continuously removing gas at multiple levels without requiring active valve control.
Solution Approach 2:
The intermediate gas outlets are positioned to automatically discharge gas from the liquid stream as it rises through the riser. The system self-regulates gas removal based on the natural flow dynamics and gas-liquid separation, eliminating the need for external control valves and complex control systems. This self-service approach maintains steady flow while controlling slug flow through passive gas discharge at multiple levels.
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 effectively suppresses regular riser slugs and mitigates other types of slugging, ensuring steady fluid flow without back-pressure, thereby enhancing production efficiency and extending the life of subsea wells.
Implementation Method 1
regulating the liquid column position using differential pressure and control mechanisms
Data Source
AI summary
A system for separating liquid and gas flowing through a multiphase pipeline, said system comprising: A riser (8) having an upper end (2) and a lower end (10), said riser being at its lower end configured to receive fluid from said multiphase pipeline (4) and having means for delivering (5) of gas at its upper end, said riser further comprising valve means (6) for adjusting the flow at which the gas is delivered through the upper end of said riser; a pipe (7) to be arranged outside or inside the riser, said pipe having an upper part (3) and a lower part (9), where the lower part is connected to or inserted into the riser, thereby creating a liquid flow path between the riser and the lower part of the pipe, said pipe having a liquid intake (11) configured to receive liquid from a liquid column in said riser, and said upper end of said pipe being configured to deliver said liquid, said pipe further comprising means for adjusting the flow at which said liquid is delivered through the upper end of said pipe; level measuring means adapted for measuring the position of a surface (18) of said liquid column in said riser; control means capable of controlling said valve means, such that the position of the surface of said liquid column can be adjusted by adjusting the flow at which gas/liquid is delivered via said liquid flow path and through the upper end of said riser and/or said lower part (9) of said pipe (7).