Casing While Drilling (CwD): Surface Hole Optimization in Mature Field of Offshore North West Java

摘要

Offshore North West Java (ONWJ) is one of Indonesia's mature fields. Mature field developments in this level require a simple, fast and cheap well design to be economically interesting. The highlight in this paper is drilling top-hole section optimization by applying Casing while Drilling (CwD). The main 2 challenges in drilling top-hole section in ONWJ are gumbo attack and loss circulation. Past mitigation was drilled a small pilot hole to reduce cutting amounts then enlarge the open-hole by hole opener. However it did not solve the problem completely. The gumbo attack still occurred, some associated non-productive rig times still happened and safety concern to clean the plugged flowline still existed. KCl Polymer mud system was not an option due to loss circulation existence, where hole will collapse when seawater is displaced to keep hydrostatic. CwD were executed successfully at 2 exploration wells in Q3 2011 by implementing Vertical-CwD (VCwD). First trial of VCwD was run only in surface section with a simple cutters casing shoe mounted on the end of a casing string. Further improvement in drillshoe, BHA and mud design was made on the second trial to extend the interval and improve overall ROP. The second trial of VCwD managed to safely drilled almost 3000ft of combine surface and intermediate vertical section with overall ROP of 60fph, where at surface section CwD was performed blindly due to total loss circulation and it was successfully cemented (no annulus pressure trap so far). The second trial has saved the company over 1MMUSD compared to conventional drilling. In 2012, numerous trials of Vertical Casing while Drilling (VCwD) have been performed for exploration and development wells in offshore North West Java. CwD is heralding the way to the future of drilling in mature fields of Offshore North West Java.