Running and Cementing the 13 3/8" Casing
The wear bushing sitting inside the 18 3/4" housing is removed. The 133/8" casing is run into the hole through the BOP stack and riser assembly. The 133/8" casing hanger is run together with a seal assembly (or packoff) which is used to seal off the 185/8”x 133/8” annulus after the cement job is complete. The entire assembly is run in hole on a casing hanger running tool and casing or drillpipe. The system is designed such that the casing can be run, landed, cemented and the seal assembly energised, all in one trip.
Having landed the casing hanger in the 183/4" housing the cement is pumped and displaced down the running string. The running string may be either casing joints, extending back to the rig, or drill pipe. In the case of drillpipe a special cement plug retainer is connected to the underside of the casing hanger running tool and the cement operation is conducted in a similar fashion to a liner cemention. At the end of the cement job the running string is rotated to the right. This releases the running tool, while simultaneously energising the packoff assembly on the outside of the hanger. When the packoff is set it can be pressure tested, and then the running tool can be picked up and pulled back to surface. Since the casing is an integral part of the BOP system it is vital that the annulus between successive casings is properly sealed off. It is good practice to flush the wellhead area prior to pulling the running string back to the surface. A wear bushing is installed above the 133/8" hanger to protect the sealing surfaces during the next drilling phase.
1.8 Drilling the 12 1/4" Hole
The 12V4" bit and BHA is made up and run to just above the cement inside the 133/8" casing. Prior to drilling out of the shoe the casing is pressure tested. To ensure that it is safe to drill ahead, a leak-off test is performed immediately after drilling out of the casing shoe. The next section of hole (12V4") is drilled to the required depth, cleaned out and the 95/8" casing is run and cemented. Exactly the same procedures are used for the 95/8" casing, as for the 133/8" casing string. If necessary, drilling can continue to greater depths by drilling an 8 1/2" hole and running and cementing 7" casing. The 3 hanger system (133/8", 95/8", 7") is the most common, but in certain parts of the world 4 hanger systems are necessary (16", 133/8", 95/8", 7").