Performance Improvement: New 16-in. TCI Design Addresses Multiple Drilling Challenges Through Interbedded Shale and Carbonate Application

Abstract

A 16-in. section is one of the most challenging sections to drill in southeast Kuwait. The section consists primarily of highly interbedded carbonates, anhydrites, shale, and marl intervals, with significant variations in compressive strength that range from 3 to 25 kpsi. There are potential loss of circulation zones in the Tayarat and Dammam formations, which complicates the drilling performance, required flow rate, and other drilling parameters to be controlled. Bit balling of the cutting structure was expected in some intervals where water-based mud was typically used. The drilling assembly was a pendulum rotary design for vertical wells. A positive displacement motor (PDM) assembly is typically used in directional wells. In addition to the loss potential and long section interval, insufficient hydraulics and the high weight on bit (WOB) necessary in the Dammam to Ahmadi carbonates led to the premature failure of the cutting structure and bearings. A durable and reliable bit design was needed to drill the entire interval and the subsequent well to help reduce overall drilling costs. Collaboration between the operator’s drilling team and the bit supplier team resulted in successfully drilling a challenging 16-in. section and multiple additional wells. Rock types, performance, and compressive strength were analyzed using an advanced software program to determine the required design changes to develop the new tungsten carbide insert (TCI) bit. The goal of the new design was to improve hydraulics configurations, create durable and robust rubber seals, and design new advanced cutting structure materials. The new bit design provided exceptional performance in multiple wells in the 16-in. section in southeast Kuwait. The bit was used to drill three wells, with a cumulative footage of more than 9,000 ft in more than 240 drilling hours. Approximately two million revolutions were achieved with effective bearings and slight normal wear to the bit cutting structure elements. The new bit design helped to drill longer intervals and multiple wells with no risk of premature failure; it also helped to reduce drilling time and bit costs. A further test was implemented in directional drilling wells where the inclination was up to 50°.