Cement Flashcards
What is TOC how is it determined?
Top of cement.
It’s determined as an engineered decision, based on geology and requirements, analysis and safety considerations. If the TOC can be left lower it gives great flexibility for the future as you can fill in to the lower point and then sidetrack a well to a new producing area. If it is too low though and there are hydrocarbon formations above the TOC point it increases the risk of a blow out ( as happened in brunei)
Key dimensions of cement / slurry design
- density
- thickening time
- fluid loss
- compressive strength
- temperature additives
How do you prevent cement floating back up into the well?
A valve is pushed down the pipe and acts as a one directional, back flow preventing valve. You can pump down through it but back flow closes the valve. A redundant second valve always sent down as a security
What is bumping the plug? What is a key risk afterwards?
Process of pressure testing the well casing after the cementing is completed.
Risk is considering the job done and forgetting well control…macondo
Once cementing is complete how are the cementing plugs removed from the well?
They aren’t removed, they’re made of concrete and soft metals so you later drill right through them.
Is the pump pressure likely to increase or decrease when pumping cement?
Increase, the cement is heavier to pump than mud
Why is a casing centralizer important during cementing?
It ensures the casing is held in the middle of the bore hole which is important because the cement will flow through the easiest path, therefore all paths should be even to ensure a consistent cementing job. If the cementing not consistent you may create channels outside casing where hydrocarbons can flow and potentially blow out.
How do you evaluate if a cement job was successful using CBL
Cement bond log. A tool that sends sonic sound waves through the casing and analyses the outcome… Essentially is it a hollow echo or compressed / muted sound. If successful will see sonic signature of the rock not the steel.
Difference between tail slurry and lead slurry?
Lead slurry is sent into the well first during a cement job. Tail slurry follows which is a heavier, possibly better quality mix that will end up at the bottom of the well which is where you want the best seal. You can’t use the tail slurry all the way through the job as it will be likely too heavy and risk fracturing the rock.
