Carbonate rock is a predominant Middle Eastern Region geologic feature. Penetration of 16" hole sections through carbonates in the Kuwait Northern Field has in the past required the use of more than one bit. This paper describes an engineering methodology that has produced bit designs that are consistently able to complete the entire 16" Kuwait Northern Field Section with a single bit as demonstrated by production drilling over the course of many bits. Case information is included.
The new design results from a symptom / cause / remedy approach that identifies root causes of unsatisfactory bit life and suggests productive, remedial solutions. Critical drilling information for prior bits was collected and analyzed to identify roller cone bit problems (symptoms). Remedies responsive to each symptom were developed. Remedy engineering was not constrained by traditional design guidelines and certain preferred solutions are considered to be unconventional. Specific, implemented remedies described by the paper include new cutting insert carbide materials and new cutting insert shapes both optimized for Middle Eastern carbonate drilling, and use of seal / bearing systems suitable for extended operation under high WOB.
The 16" hole section thickness in the Northern Kuwait fields can range between 4000 ft to 5000 ft. The section is predominately comprised of carbonate rock, (limestones, anhydrite, and dolomite) with variable compressive strengths ranging from lows of a few thousand psi to highs of around 30,000 psi, (Fig. 1). These formations, while not particularly abrasive, have relatively high strengths and are very tough and difficult to drill and penetration requires high weights on bit. Through the years, the section has rarely been completed with a single bit run. Engineering described by this paper was prompted by the economic opportunities to be gained through bits capable of completing the section in a single run.
This paper describes the general diagnostic / organizational method through which a specific purpose bit has been designed and provides details and background information for incremental design elements for the resulting successful design.