Valve Lubricants for Carbon Capture and Storage Operations
Understanding how Valve Lubricant 601 behaves when mixed with Supercritical CO2.
Valve lubricants for carbon capture and storage operations
Carbon Capture and Storage (CCS) is the process of capturing waste carbon dioxide (CO2) and storing it where it will not enter the atmosphere. The aim is to prevent the release of large quantities of CO2 into the atmosphere to help reduce the impact of heavy industry processes on the environment and limit climate change. With an increased focus and need to limit our carbon footprint, the Carbon Capture and Storage market is expected to increase significantly over the coming years.
These storage areas are normally in underground geological formulations and require injecting liquified or supercritical CO2 into the reservoir, either as part of an Enhanced Oil Recovery (EOR) technique, or simply to just store it in the rock formation to prevent release into the atmosphere.
Injecting liquified or supercritical CO2 into reservoirs poses certain challenges to the equipment involved, not least the valves on the Injection Christmas trees and the valve lubricants used in them.
It is paramount to ensure that the valve grease used in these API 6A gate valves is not freely miscible with the CO2 fluid so that it keeps its grease-like properties and is retained in the valve cavity to ensure long lasting protection of the valve internal components.
Operating temperatures and pressures
The operating pressures and temperatures used in the analysis were specific to the carbon capture and storage project being carried out by the operator (2500 psi and 120°C). The graph below shows the amount of CO2 absorbed by the Valve Lubricant 601TM base fluid at 120°C (operating temperature) at varying pressures. At 2500 psi (operating pressure) only 5.4% of the supercritical CO2 is absorbed by the base fluid, meaning that it is not freely miscible/does not form a supercritical fluid with the CO2.
At 5.4% CO2 absorption, Valve lubricant 601TM retains approximately 70% of its viscosity, meaning the lubricant will remain grease-like and be retained in the valve cavity.
If an operator was to use a valve grease that was not as stable in these conditions, and the CO2 absorption rate was higher, then it would dilute the grease to the point where much more of its viscosity is lost. This would result in the grease more freely flowing out of the valve cavity causing potential problems downhole blocking up in the formation, and leaving the valve unprotected and exposed to wear on the gates and seats and corrosion. If the grease did form a supercritical fluid with the CO2, it could potentially strip the grease of the base oil and leave behind the grease thickener and solids, causing drying out and hardening of the grease and possible valve actuation issues.
This lab analysis together with a long history of Valve Lubricant 601 being used in CO2 injector trees gives service companies and operators confidence that their valves will be fully protected when using Valve Lubricant 601TM.
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