Surface Casing
The amount of surface casing used will depend on the depth of the unconsolidated formations. Surface casing is usually set in the first competent formation. Normal size for surface casing is between 20 inch and 13-3/8 inch (outside diameter). Since temperature, pressure and corrosive fluids tend to increase with depth, different grades of casing will be required to handle the different well conditions.
Purposes of surface casing are to:
• protect fresh water formations
• seal off unconsolidated formations and lost circulation zones
• provide a place to install the B.O.P.'s
• protect “build” sections on deviated wells
• provide for a sufficient “leak-off” test to be conducted
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