Subsea Pipeline Drain Layout for Liquid Holdup and Continuous Pigging
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Solution Overview
Problem
Subsea pipelines face challenges in transporting production gas over long distances due to gravitational pressure losses and slugging issues, which reduce the production plateau and prevent continuous pigging operations, as existing liquid removal systems are inefficient and not designed for continuous operation.
Innovation Solution
A drain apparatus that can be positioned anywhere along the subsea pipeline to remove liquids, featuring a liquid extraction system with strategically placed inlets and outlets to maintain pressure differential and allow continuous pigging, and includes a pump system for efficient liquid removal and hydrate inhibitor injection to prevent hydrate formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a single separator is incorporated at the well head, then some liquid is removed from the multiphase flow, but the system does not achieve pseudo dry gas status and liquid accumulation continues downstream
Solution Approach 1:
The patent divides the single separator function into multiple distributed drain apparatuses positioned at different locations along the pipeline. Each drain apparatus includes a separator chamber and extraction chamber that work together to remove liquid locally, preventing downstream accumulation and achieving pseudo dry gas status throughout the entire system.
Solution Approach 2:
The invention adds a spatial dimension to liquid removal by distributing drain apparatuses along the pipeline length rather than concentrating all separation at the well head. This dimensional distribution allows continuous liquid extraction at multiple points, transforming the system from centralized to distributed architecture.
2Quantity of substance
If subsea drains are positioned at the lowest part of a gradient, then liquid flowing back down the pipe is removed, but system efficiency is not significantly improved and continuous pigging operations are prevented
Solution Approach 1:
The drain apparatus incorporates movable components including a pig that can travel through the extraction chamber, and a valve system that dynamically opens and closes to control liquid extraction while allowing pig passage. The system adapts its state based on whether liquid removal or pigging operations are occurring.
Solution Approach 2:
The patent enables continuous pigging operations by designing the extraction chamber with sufficient length and appropriate opening positioning to allow pigs to pass through uninterrupted. The valve system maintains continuous liquid removal capability while periodically allowing pig passage, ensuring uninterrupted pipeline maintenance operations.
3Stress or pressure
If the bore of the main carrier pipe is increased, then gravitational pressure losses increase causing worse slugging, but decreasing the bore increases pressure loss due to friction
Solution Approach 1:
The patent extracts liquid from the multiphase flow at multiple distributed points along the pipeline using drain apparatuses with separator and extraction chambers. By removing liquid continuously throughout the pipeline rather than allowing it to accumulate, the system reduces gravitational pressure losses and slugging effects without requiring changes to pipe bore size.
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
Enables the transportation of gas over greater distances by effectively removing liquids, maintaining system integrity, and reducing pressure drop, thus increasing the production plateau and allowing continuous pigging operations while minimizing hydrate inhibitor usage.
Implementation Method 1
such that a pressure differential can be maintained across the pig
Implementation Method 2
includes a pump system for efficient liquid removal
Implementation Method 3
includes a pump system for efficient liquid removal and hydrate inhibitor injection to prevent hydrate formation
Data Source
Figure 1
Figure 2a~2c
Figure 3a~3b
AI summary
The present invention provides a drain apparatus (200) for use in a subsea pipeline to remove liquid from a multiphase flow in the subsea pipeline. The drain apparatus comprises a first channel (20) for carrying a multiphase flow comprising liquid and gas phases; and liquid extraction means (11, 12, 14, 18) for extracting the liquid phase from the multiphase flow in the first channel (20). The internal diameter of the first channel (20) is substantially the same as an internal diameter of a subsea pipe arranged to carry the multiphase flow in the subsea pipeline, such that a pig travelling along the subsea pipe can pass through the first channel (20). The present invention also provides a subsea pipeline comprising a subsea pipe for transporting a multiphase flow subsea; and at least one drain. The at least one drain is disposed partway along a gradient in the subsea pipe to reduce liquid holdup.