Abstract
An offshore field has presented a challenging intermediate drilling application. The 2200-m section was drilled in a 17.5-in. hole to 3700-m true vertical depth. The lithogy of the section is variable, beginning with a soft claystone, followed by several sandstone formations, an 1100-m interbedded sandstone and claystone interval, a 125-m hard carbonate, and 50m of softer claystone before the casing point. The challenges presented in recent offset wells included high stick/slip, high levels of drill bit cutting structure wear and drill bit body erosion. Polycrystalline diamond compact (PDC) bit designs utilized in recent offsets varied from six to nine blades, with the interval requiring two or three bits to complete the interval.
Based on results from other challenging offshore applications, including improved durability and drilling dynamics, the next-generation PDC and roller-cone hybrid drill bit (hybrid) with improved design features was selected for the application. Improved design features included a new increased blade count concept, combined with a sharp and dense roller-cone cutting structure.
The application of the next-generation hybrid drill bit design delivered a reduction in drilling time and an improvement to drilling dynamics compared to offset wells drilled with conventional technology. Compared to the best offset well drilled in 17.5-in. hole a reduction in total drilling time of 59.4hrs (31%) was achieved. The reduction in drilling time resulted from both an increase in on bottom ROP of 32% and the removal a bit trip (19 hours) due to the interval being drilled in one run for the first time. Associated with the reduced drilling time, improvements in drilling dynamics were observed with stick/slip reduced by 73%.
This paper illustrates the study of the application, applied learnings from new technology developments in hybrid technology evolution, and the subsequent improvements in drilling dynamics that resulted in improved penetration rates and cost savings in this challenging application.
