IN the onshore fields of the Gulf Province of Papua New Guinea, top hole section formations notoriously present challenges in surface drilling and well construction operations.

Presence of potential shallow gas zones and losses have been documented as major concerns in the area, where conventional drilling and casing running techniques are inadequate to meet the challenge.

Weatherford-2In Q4 2016, an international oil company operating in Papua New Guinea requested Weatherford to implement its Drilling with Casing (DwC) services, so as to mitigate hazards and get through trouble zones. This technique permits the simultaneous drilling, running, setting, and cementing of casing while eliminating downhole complexity.

Responding quickly to the request, Weatherford designed and deployed two sections of Drilling with Casing systems in a single well. One of them included a 24-in DwC system that allowed the operator to simplify the well design by omitting a 30-in conductor pipe installation from the original well architecture and to replace it with 24-in conductor pipe to be set deeper and at same time cover the potential shallow gas zone.

The initial plan was to deploy a 24-in casing by 28-in hole drillable casing bit that was planned to be set at 100 meters. Due to diameter restriction of the rig rotary table, the outside diameter (OD) of the casing bit was later reduced to 27-in, instead of 28-in.

Based on previous drilling experiences on offset wells and further reviews on the formation data provided by the operator, the drillable casing bit was then designed with six total blades and furnished with 19mm polycrystalline diamond compact (PDC) cutters suitable for drilling medium to medium-hard formations with unconfined compressive strength (UCS) up to 20,000 psi.

The nose section of the bit was made from aluminum to permit the conventional PDC or roller cone drill bit to drill out the shoe without causing excessive damage and enable drilling of subsequent formations.

The casing bit was also furnished with ceramic nozzles in order to provide resistance against potential high flow rates and abrasive material within the drilling mud system that may erode and wash the casing bit nozzles out. The nozzles fitted on the casing bit were 14 x 10/32-in with total flow area of 1.074-in2.

The casing bit was manufactured with prep weld connection due to requirement of welding on to a casing that has a premium connection cut on the box section. The connection combines the advantages of a preloaded, thread-type connector with the rapid make-up. In order to prevent back-off during drilling operations and to permit the connection to transmit torque, integral anti-rotation tabs were engaged using a manual shear tool.

The 24-in conductor specification run on the well was a 24-in x 0.75-in WT API 5L, X56, R3. The internal casing drive tool (ICDT) – a fully mechanical activated tool – was proposed and utilized as surface casing drive and drilling system. It was connected to the rig’s top drive system though a 6-5/8-in REG pin x NC50 box crossover and a 10ft drill pipe pup joint with a NC50 connection that serves a flexibility function for the ICDT when stabbing into the casing.

The system required a full slack-off and quarter rotation to the right to engage the casing, and anticlockwise rotation to release the tool from the casing.

A double-valve float collar and a stab-in double-valve float collar were then installed on the string as a mechanical well barrier in the event of well control and for cementing purposes. The 24-in conductor string were successfully drilled to final depth of 101 meters and cemented in place with zero non-productive time.

Lessons learned were then applied with another smaller 18-5/8-in DwC system, allowing the operator to set the surface casing to planned depth through potential gas and loss zones.

Similar casing bit type and model run on the offset wells, was selected and utilized to drill the 22-in hole formation to section total depth of 600m. The 18-5/8-in drillable casing bit has eight total blades that are furnished with 19mm PDC cutters and fitted with 14 x 10/32-in ceramic type nozzles.

The casing bit was made up to an 18-5/8-in, 87.5ppf, K55 with BTC connection. Due to API BTC connection type utilized on all casing string, torque rings were installed to increase torque resistance during drilling with casing operation.

Utilising same surface casing drive and drilling tool as well as its configuration as on the 24-in DwC operation, the 18-5/8-in casing safely drilled to section total depth of 600m MD without significant issue incurred.