For the ultra-deep ultra-high pressure wells in the Kuqa foreland basin of the Tarim basin in western China, it has been an ongoing challenge for more than a decade to drill through the Cretaceous Bashijiqike (K1bs) formation in a more efficient and economical manner. It is comprised of sandstone and mudstone with abundant natural fractures in the upper K1bs with frequent severe fluid loss occurrence and middle and bottom K1bs are both comprised of highly compacted sandstone, mudstone and siltstone without the presence of natural fractures. In the past, it requires an average of 8, and sometimes up to 16, premium PDC bits and more than 90 days to complete the target interval. This paper discusses the continuous effort in the development and introduction of ongoing bit technologies to drill through the Bashijiqike Formation and the development of methodology that tailors different bit technologies to different sections of the Bashijiqike formation according to drillability characteristics. Dissecting the formation into different sub-zones and matching them with suitable bit technologies results desirable efficiency and significant cost reduction.

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