Operator in North Western Kazakhstan, onshore Karatobe Yuzhnyj field was engaged in a task of reducing the well construction time in particular the challenging 12 ¼ in. section. The main complexity of drilling the 12 ¼ in. section is the presence of corrosive salt deposits traditionally drilled with matrix bodydrill bits aggravated by drilling with water-based mud (WBM) system. While matrix body drill bit is the primary choice in salt saturated drilling fluid and corrosive environment, consequences of this choice have a significant impact on the bit's poor rate of penetration (ROP) response.
The long 12 ¼ in. section is usually drilled in 3-4 bit runs with relatively low ROP and poor bit performance primarily occurs due to bit balling in shale section and Weight On Bit (WOB) limitations in interbedded carbonate section.
During the planning stage for the drilling campaign the Operator engaged with Zhigermunaiservice LLP drill bit engineering group to develop a fit-for-purpose solution for ROP optimization. New 12 ¼ in. ZS56 steel body drill bit with unique hardfacing design, improved hydraulics and shaped PDC cutters was developed and delivered on time for the drilling campaign. During the very first run the newly designed steel body bit demonstrated an outstanding performance in drilling highly corrosive salt deposits and other lithological sequences thus delivering the section from shoe to TD at record ROP. This bit was re-used to drill four consequent wells with similar performance.