Subsea Flowline Dewatering With Multiphase Pump Suction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current methods for dewatering subsea gas flowlines are cumbersome, expensive, and time-consuming, particularly due to the need for extensive compression plants to achieve the required pressure ratio, especially in deepwater applications.
Innovation Solution
A subsea fluid flowline dewatering system that includes a multiphase pump at the lower end of the flowline to support the downward travel of a pig train, with a meter for density detection and a flow mixer unit to estimate gas volume fraction, and a controllable seawater inlet to manage gas content, allowing for efficient dewatering with reduced topside compression power and energy consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If compressed gas is used to drive a pig train from subsea to shore, then dewatering can be achieved, but extensive compression plant is required due to large pressure ratio
Solution Approach 1:
Instead of pushing the pig train from the lower end with compression, the invention uses suction from the upper end to pull the pig train downward. This inversion of the driving mechanism eliminates the need for extensive subsea compression plants and reduces the pressure ratio requirement, as the pump only needs to create suction rather than overcome full ambient pressure.
Solution Approach 2:
The invention replaces the mechanical compression system with a pump-based suction system. Rather than using compressed gas to push the pig, a pump creates negative pressure (suction) that pulls the pig downward through the flowline, substituting a more efficient mechanical approach for the gas compression method.
2Reliability
If compressed gas is used to drive a pig train, then dewatering can be achieved, but the process is expensive and time consuming
Solution Approach 1:
By inverting the dewatering approach from push-based compression to pull-based suction, the system achieves faster pig travel times and continuous operation. The suction method allows the pump to maintain consistent flow rates without the pressure ratio limitations that slow down compression-based methods.
Solution Approach 2:
The pump-based suction system enables continuous dewatering operation without the intermittent cycles required by compression methods. The pump can continuously pull the pig and water through the flowline, maintaining steady-state operation that improves productivity and reduces overall dewatering time.
3Ease of operation
If pig train is driven with gas pressure slightly higher than ambient seawater pressure, then pig can travel towards shore, but deepwater applications require 2-300 bars pressure
Solution Approach 1:
Instead of pressurizing gas to push the pig from the bottom, the system uses suction from the top to pull the pig downward. This eliminates the need to overcome high ambient seawater pressure, as the pump only needs to create a pressure differential sufficient to pull the pig, not push it against 2-300 bars of ambient pressure.
Solution Approach 2:
The suction-based system creates a more favorable pressure distribution along the flowline. By pulling from the upper end, the system exploits the natural pressure gradient in the vertical flowline, reducing the pressure stress requirements compared to pushing from the lower end against high ambient pressure.
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 enables efficient and continuous dewatering of subsea gas flowlines with reduced energy requirements, lower final gas pressure, and increased safety, making the process faster and more efficient compared to traditional methods.
Implementation Method 1
the multiphase pump being configured to provide suction at the lower end of the flowline thereby supporting downward travel of the pig train towards the lower end of the pipeline
Implementation Method 2
a meter for density detection to estimate GVF
Implementation Method 3
The mixer unit is configured to mix gas and liquid phases of fluid to enable adequate GVF estimations from the meter
Implementation Method 4
the sea water inlet including a choke valve that is configured to allow additional sea water into the fluid entering the multiphase pump to ensure the GVF is not greater than the multiphase pump can adequately handle
Data Source
AI summary
A system for dewatering a subsea gas pipeline includes a pig launcher at the pipeline's upper end, which may be at or near the sea surface, and a pig receiver at the pipeline's lower end, which may be at or near the sea floor. A multiphase pump unit is deployed at the pipeline lower end and is configured to provide sea water suction to aid in a pig train being forced downwards through pipeline. The multiphase pump is configured to handle some amount of gas leaking around the pig train. A choke system may allow sea water to enter the flowline, thereby lowering the gas volume fraction (GVF) and preventing the GVF from exceeding the ability of the multiphase pump. For deeper water applications, a second pump may be provided in series that may be a single pump if positioned downstream of the multiphase pump.