The >12km number is length, not depth:

> However, in May 2008, a new record for borehole length was established by the extended-reach drilling (ERD) well BD-04A, in the Al Shaheen oil field. It was drilled to 12,289 m (40,318 ft), with a record horizontal reach of 10,902 m (35,768 ft) in only 36 days.