Drilling difficult sediments and hard chalk, offshore UK
Offeset data stated a minimum of two bit run was needed to reach TD in a Central North Sea well. By deploying an AST and aggressive cutters, the section was drilled in one fast run with minimal wear.
The 16″ section was planned as a 7,120ft section drilled vertically from the 13 3/8″ shoe in the Nordland Group through the Westray, Stronsay, Moray and Montrose Groups to TD in the Chalk (Hod) at 11,220ft. Section objectives were to complete the section with as few trips as possible, maintain verticality and optimise ROP. Based on offset data, a minimum of two bit runs would be required to complete the section.
The section length of 7,110ft was drilled in one bit run with an average ROP of 52ft/hr. ROP through the chalk section was higher than expected with steady torque maintained. No vibrations were recorded and verticality was maintained without the need to slide. The bit was in excellent condition (1.2) at the end of the run and recommended for repair.
The 16″ section was drilled 8 days ahead of the planned AFE and delivered a cost saving in excess of £2 million.