Ann: Lockyer Deep-1 Operational Update, page-45

Most cases with cement in casing get abandoned. Its just not worth it. At a spread rate of anywhere between 150 to 200K a day and drilling cement inside a 5-1/2" casing to 4000m. Nope not advisable and certainly not economical. Cement used in casing ops is very hard, At 1m an hour is 4000hrs. 166 days. If there is no rig break down, no pulling out of hole to change bits or mill. You can pretty much calculate the cost.
Really not worth it. If the cement is only a few hundred meters well then its fine. Else this is a real tough chance. Believe they would have tried pulling the casing and have reverted to milling if that had failed.