Orubadi formation in Permit PRL 21 at Western Province Papua New Guinea(PNG) was known for its challenges to drilling and casing-running operations on the surface section. A waterflow event occurred when drilling the offset well through the formation, consequently requiring the flow to be diverted. In addition, the surface casing-running operation was time-consuming due to tight-hole conditions, which led the operator to perform extra trips to reamthrough the ledges.
An approach using the drilling-with-casing technique was presented and identified as the most suitable drilling method for setting the 13 3/8-in. surface casing safely and improving drilling efficiency through trip-time reduction and elimination of conventional drilling BHA handling. A unique, reliable and easily operated top-drive casing-running and drilling system, which had been used regularly for surface casing-running operations, has contributed to the first successful drilling-with-casing operation on the rig. The casing-bit selection has appeared to be an important process in this challenging project. Ultimately, a newly-developed polycrystalline-diamond-compact (PDC) drillable casing bit with PDC cutters was selected based on the estimated hard formation rock strength characteristic of the field, in order to achieve the targeted total depth in a single trip.
The drilling-with-casing system was deployed through the problematic zone and mitigated the expected borehole problem with variations in the drilling penetration rate. Recommended drilling parameters were used to achieve optimum performance in combination with sufficient mud properties to maintain good hole cleaning and bit hydraulic performance until total depth.
This paper presents the drilling-with-casing project in the field, covering the planning stage, equipment selection, preparation, implementation, and operational aspects of the longest nonretrievable 13 3/8-in. drilling-with-casing project performed in the world to date.