Subsea Grease Injection Module for Pressure Control Heads
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Solution Overview
Problem
Current subsea grease injection methods for pressure control heads (PCH) are inefficient due to the need for high-pressure grease injection and manual monitoring, especially in deepwater environments, where long grease lines and viscous grease pose challenges, and there is a risk of water ingress leading to hydrate plugging.
Innovation Solution
A pressure-compensated grease injection system using a subsea accumulator and electric motor-driven pump, with pressure sensors to regulate grease injection pressure above ambient and well pressures, eliminating the need for surface grease lines and using environmentally friendly lubricants.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If grease is injected at high pressure to compensate for ambient pressure and prevent water ingress, then sealing effectiveness is improved, but the complexity of the injection system increases
Solution Approach 1:
The system uses ambient pressure sensors to automatically regulate grease injection pressure, eliminating the need for manual monitoring and adjustment. The pressure compensation mechanism self-adjusts based on real-time ambient pressure readings, ensuring adequate sealing without requiring complex manual intervention systems.
Solution Approach 2:
The system incorporates pressure sensors that continuously monitor ambient pressure and provide feedback to the injection control mechanism. This closed-loop feedback system dynamically adjusts grease injection pressure to match ambient conditions, maintaining effective sealing while simplifying overall system operation through automated control.
2Adaptability or versatility
If long grease lines are used to supply grease to deepwater PCH, then the system can operate in deeper water, but the difficulty of pumping viscous grease increases
Solution Approach 1:
The system pre-charges the grease accumulator with grease before deployment to the deepwater location. This preliminary action ensures that grease is already positioned and pressurized in the accumulator, eliminating the need to pump viscous grease through long lines during operation and reducing the power requirements for grease delivery.
Solution Approach 2:
The grease accumulator acts as an intermediary device that stores and pressurizes grease locally at the PCH. This intermediary eliminates the need for long surface-to-subsea grease lines, as the accumulator serves as a local reservoir that can supply grease without requiring continuous high-pressure pumping from the surface.
3Device complexity
If manual visual monitoring is used to determine grease injection needs, then the system is simpler, but the time required for monitoring and response increases
Solution Approach 1:
The system replaces manual visual monitoring with electronic pressure sensors and automated control mechanisms. Pressure sensors continuously monitor the grease injection pressure and ambient pressure differential, automatically triggering injection when thresholds are reached, thereby eliminating the time loss associated with manual monitoring while keeping the overall system relatively simple.
Solution Approach 2:
The system implements automated feedback-based pressure monitoring that continuously tracks grease injection pressure and ambient conditions. When the pressure differential indicates a need for grease replenishment, the system automatically responds by activating the injection pump, eliminating the time delay inherent in manual visual inspection and decision-making.
4Reliability
If grease is replenished at higher rates to compensate for unknown losses, then sealing reliability is improved, but grease waste increases
Solution Approach 1:
The system uses pressure sensors to provide real-time feedback on the pressure differential between the grease-filled PCH and the ambient environment. This feedback enables precise control of grease injection, replenishing grease only when the pressure differential indicates actual loss, thereby maintaining sealing reliability while minimizing unnecessary grease waste.
Solution Approach 2:
Instead of continuously injecting grease at high rates, the system applies partial action by injecting grease only in the specific amounts needed to maintain the required pressure differential. This targeted approach replaces the excessive action of continuous high-rate injection, ensuring adequate sealing while significantly reducing grease waste.
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 ensures consistent, efficient grease injection with reduced waste and eliminates the risk of water ingress, maintaining effective sealing without hydrate plugging, even in deepwater conditions, by monitoring and controlling pressure differentials and using fish-oil based lubricants.
Implementation Method 1
pressure in the well and in the fluid surrounding said subsea intervention system is read by the accumulator, which as a consequence of this delivers a grease injection pressure at a level that is above said pressures
Implementation Method 2
controlling the pump to regulate the grease injection pressure at a level that is above said outside pressure
Implementation Method 3
providing a connection with an outside pressure sensor, receiving signals from said pressure sensor
Data Source
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AI summary
There is described grease injection system for a subsea lubricator where the grease injection system is a module (21) attached to the pressure control head (PCH) and is hoisted and lowered together with the PCH. In one aspect of the invention the module (21) can operate when it is disconnected from the main control system. In another aspect of the invention grease pressure is maintained at a level only slightly above the well pressure so that grease usage is minimized.