The compact spool was developed as an alternative to the conventional spool discussed above. A compact spool enables several casing strings or tubing to be suspended from a single spool. The first step in using this type of wellhead is to install the 20″ casing head housing, as in the case of the spool type wellhead. After the 13 3/8” casing is run and cemented, the casing is cut off and the speedhead is connected to the casing head housing. The BOPs can then be connected to the top of the housing, and the next hole section drilled.
The 9 5/8″ casing is then run, with the hanger resting on a landing shoulder inside the speedhead. A 7″ casing string can be run, and landed, in the speedhead in a similar manner to the 9 5/8″ casing. The tubing string may also be run and landed in the speedhead. The Christmas tree can then be installed on top of the speedhead.
The disadvantage of the compact spool is that the casing programme cannot be easily altered, and so this system is less flexible than the separate spool system.