1
Q
What are the main purposes of surface casing
A
- Protects fresh water sands
- Case unconsolidated formations
- Provide Primary Pressure Control- BOP stack is usually nippled on surface casing
- Support future casing
- Case off potential lost circulation zones
- Casing head and other completion fitting used in completing the well are attached later
2
Q
Characteristics of surface casing
A
- Casing sizes usually run from 7 5/8” for shallow wells to 20” on deep multistring wells
- Hole may be severely eroded.
- Shallow surface strings can be pumped out easily
- Drilling muds often viscous with little water loss control
- Casing may stick easily in unconsolidated formations
- Loss circulation may be a problem
- Most areas want cement to surface for surface casing
- Guide shoe or float shoe, float collar, cementing plugs, scratchers, and centralizers are commonly used
3
Q
What is the most important feature of surface casing
A
Protecting fresh water reservoirs
4
Q
What are recommended cement properties for surface casing
A
- Completion cements with accelerated thickening times and compressive strengths are used.
- Deeper strings use lightweight lead cements followed by heavier-weighted completion (tail) cement
- With a Lead and Tail Cement Blend, lead filler cements (High Water Ratio) followed by neat or high strength tail cement that is accelerated
- Lost circulation material is usually added
- High strength cements should be used on deep well surface casings to support future strings
5
Q
What are surface casing cementing practices
A
- Large Diameter surface strings are cemented through drill pipe with sealing sleeve
- Bottom and top plugs are used to reduce mud contamination
- Bottom joints are centralized and thread locked to prevent backing off while drilling
- Regulatory rules usually require a WOC time of 4 to 8 hours or minimum of 500 psi compressive strength cement before resuming rig operations
- Avoid using bottom plug when using lost circulation material
- Differentail pressure may require that the pipe be chained down to prevent pipe pump out
- If inn string method is used, enough weight needs to be applied to the drill pipe so it won’t be pumped off the landing surface
6
Q
Where is the float collar placed on surface casing
A
Two joints above the guide show so as to prevent mud from contaminating the cement around the shoe joint
7
Q
Why are scratchers used
A
Scratchers help circulate mud from formation walls
8
Q
Why are centralizers used
A
Centralizers center the casing in the hole to help circulate cement completely around the pipe
