Subsea Pipeline Drain Channel for Piggable Liquid Removal
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing subsea pipelines face challenges in transporting production gas over long distances due to liquid precipitation, which causes gravitational pressure loss, slugging, and reduces the production plateau, while current designs of subsea drains do not effectively remove liquid and allow continuous pigging operations.
Innovation Solution
A drain apparatus is introduced for subsea pipelines that includes a first channel for multiphase flow with liquid extraction means, allowing a pig to pass through and positioned anywhere along the pipeline to remove liquid, featuring liquid extraction means with openings configured to maintain pressure differential and optional valves for controlling flow, and a subsea pipeline design with drains disposed partway along the gradient to reduce liquid holdup.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If subsea drains are positioned at the lowest part of a gradient to remove liquid, then liquid removal is achieved, but system efficiency is not significantly improved and continuous pigging operations are not allowed
Solution Approach 1:
The drain apparatus is segmented into a first channel for multiphase flow and a second channel for liquid extraction, allowing the pig to pass through the first channel while liquid is extracted through the second channel. This segmentation enables continuous pigging operations while maintaining effective liquid removal.
Solution Approach 2:
The first channel acts as an intermediary structure that allows the pig to pass through while the liquid extraction means intercepts liquid from the multiphase flow. The opening in the first channel wall serves as the intermediary interface between the two channels, enabling liquid transfer without blocking pig movement.
2Stress or pressure
If the bore of the main carrier pipe is increased to reduce gravitational pressure losses, then pressure drop per unit distance is lowered, but slugging worsens due to increased gravitational pressure losses
Solution Approach 1:
Liquid is extracted from the multiphase flow through the liquid extraction means, removing the harmful liquid phase that causes slugging. This extraction allows the use of larger bore pipes without worsening slugging, as the liquid content is continuously removed to maintain flow stability.
3Quantity of substance
If subsea drains are designed with larger opening distance to facilitate liquid extraction, then liquid removal efficiency increases, but pressure differential maintenance across the pig is compromised
Solution Approach 1:
The opening in the first channel wall is designed with a distance less than 1.5 times the internal diameter of the first channel, which is sufficient to extract liquid effectively while maintaining pressure differential. This partial action approach achieves adequate liquid removal without excessive opening size that would compromise pigging 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 solution enhances gas transport distance by effectively removing liquid, maintaining pressure, and allowing continuous pigging operations, thereby increasing production plateau and reducing pressure loss.
Implementation Method 1
a pressure differential can be maintained across the pig
Implementation Method 2
a pig travelling along the subsea pipe can pass through the first channel
Data Source
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.