Subsea Hydrocarbon Evacuation via Liquid-Gas Displacement
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Solution Overview
Problem
Existing methods for evacuating hydrocarbons from subsea process modules, such as compressors, often leave trapped hydrocarbon gas or liquid in pockets due to their lower density compared to displacement mediums like MEG, posing safety risks during retrieval.
Innovation Solution
A method involving connecting a receiving container line to the upper fluid connection point and a liquid adding line to the lower point, displacing hydrocarbons with a high-density liquid medium, and then diluting remaining hydrocarbons with a non-hazardous gas medium like nitrogen to ensure complete evacuation, particularly effective for modules with complex internal geometries and trapped pockets.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If high density monoethylene glycol is injected into the subsea process module to displace hydrocarbon, then hydrocarbon evacuation is achieved, but hydrocarbon trapped in high-pockets remains undisturbed due to lower density
Solution Approach 1:
The method applies preliminary action by first injecting liquid displacement medium to evacuate the majority of hydrocarbon, then subsequently introducing gas displacement medium to address remaining trapped hydrocarbon in high-pockets. This two-stage approach ensures complete hydrocarbon removal by preparing the system for the final evacuation of difficult-to-reach pockets.
Solution Approach 2:
The invention changes the physical parameter of the displacement medium from liquid (high density) to gas (lower density) to match the density characteristics of trapped hydrocarbon in high-pockets. This parameter change allows the gas medium to effectively displace the remaining hydrocarbon that liquid medium cannot reach, ensuring complete evacuation.
2Productivity
If liquid displacement medium is used to evacuate hydrocarbon, then most hydrocarbon is removed, but trapped hydrocarbon in high-pockets cannot be displaced
Solution Approach 1:
The invention changes the physical parameter of the displacement medium from liquid to gas to match the density characteristics of trapped hydrocarbon in high-pockets. This parameter change allows the gas medium to effectively displace the remaining hydrocarbon that liquid medium cannot reach, ensuring complete evacuation while maintaining high productivity.
Solution Approach 2:
The method ensures continuity of useful action by seamlessly transitioning from liquid displacement medium injection to gas displacement medium injection. The gas medium continues the evacuation process where the liquid medium left off, eliminating trapped hydrocarbon in high-pockets and ensuring complete removal without interruption.
3Reliability
If strict safety measures are implemented for residual hydrocarbon, then safety risk is managed, but operational complexity and cost increase
Solution Approach 1:
The method applies preliminary action by completely evacuating hydrocarbon from the subsea process module before retrieval using two-stage displacement. This preliminary evacuation eliminates the need for complex safety measures during retrieval operations, as the module is already free of trapped hydrocarbon that could pose safety risks.
Solution Approach 2:
The invention converts the potential harm of trapped hydrocarbon into benefit by using the density difference between gas displacement medium and hydrocarbon to achieve complete evacuation. The lower density gas medium naturally rises to displace trapped hydrocarbon in high-pockets, turning what could be a safety hazard into an effective evacuation mechanism.
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
This method minimizes the risk of trapped hydrocarbons by ensuring all hydrocarbons are displaced and diluted to safe concentrations, allowing for safe retrieval of subsea process modules without the need for stringent safety measures.
Implementation Method 1
High density monoethylene glycol, MEG, is injected into the subsea process module at a lower section of the module. This causes the hydrocarbon contained in the module, which as a lower density than the MEG, to be evacuated through an evacuation line at an upper section of the module.
Implementation Method 2
diluting the remaining hydrocarbon by a gas medium added through the gas adding line by diluting a gas-phase portion of the hydrocarbon that has been trapped in a pocket in the subsea process module
Data Source
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AI summary
Method for evacuating hydrocarbon from a subsea process module (210), the subsea process module having an upper fluid connection point (222) and a lower fluid connection point (232), the method comprising: connecting (110) a receiving container line (220) to the upper fluid connection point (222) of the subsea process module (210); connecting (120) a liquid adding line (230) to the lower fluid connection point (232) of the subsea process module (210); displacing (130) hydrocarbon by a liquid displacement medium added through the liquid adding line (230); removing (140) the liquid adding line from the lower fluid connection point (232); connecting (150) a gas adding line (260) to either the upper fluid connection point (222) or a lower fluid connection point (232); connecting (160) a receiving container line (220) to the lower fluid connection point (232) and or another lower fluid connection point; diluting (170) the remaining hydrocarbon by a gas medium added through the gas adding line (260).