Interbedded formations with vastly different compressive strengths and blind drilling are two distinct challenges the operator must solve constructing a 16″ hole section in Northern Kuwait. These issues can lead to cutting structure damage to roller cone bits resulting in low performance and downhole tool failure. In addition the operator strives to achieve fast ROP by applying high weight-on-bit (WOB) through the hard Dammam to Mutriba carbonate sections which can also cause damage to the tungsten carbide insert (TCI) bit's cutting structure.
To manage the challenges, the operator's drilling team working in conjunction with the bit supplier launched a performance improvement initiative. The carbonate application was analyzed using finite element analysis (FEA) based dynamic simulation program to fully understand how to stabilize the bit in different downhole conditions and improve hydraulic efficiency. Based on the computer analysis and field run data, a new stable bit was designed.
The new bit includes a specialized cutting structure configuration, improved hydraulics and optimized insert carbide grades to mitigate impact damage. A patented double sealed bearing was also utilized to improve durability and seal reliability
The new roller cone bit design was run with an optimized drilling plan setting a record rate of penetration (ROP) in its first test run. The new bit design has enabled the operator to drill a challenging carbonate section of 4775 ft from Shoe to total depth (TD) with a record penetration rates (ROP) of 65.8 ft/hr achieving 7.7 % increase in ROP over the best performance in the same field. The authors will discuss the application challenges, analysis and resulting performance improvement.