Experience With Stratapax Drill Bits

Abstract Polycrystalline Diamond Compact (PDC) bits have been extensively used in Polycrystalline Diamond Compact (PDC) bits have been extensively used in oil field drilling for sometime. Major performance gains have been reported for use of these bits in oil based drilling fluids, operating on mud motors. This paper describes the experience in Sarowak and Sabah Shell Operations with PDC bits in water based drilling fluids and with rotary drilling. It represents the results of over 80 individual PDC bit runs incorporating over 30,000' of 8 1/2" hole drilled with 4 types of PDC bits from 3 manufacturers, and over 14,000' of 12 1/4" hole with 8 bit types from 4 manufacturers. The paper discusses the PDC bit runs made, the performance in relation to conventional tri-cone bits, the effects of conventional hydraulics on PDC bit performance and the design of the PDC bits in terms of cutter density and placement, number of nozzles and their placement, and construction methods. The outlook for future designs of PDC bit with respect to use in water base drilling fluids and on rotary drilling is presented. The experience presented con be applied to drilling operations in a wide variety of areas to optimise usage of PDC bits in water based drilling fluids and on rotary drilling. As a result of extensive testing within Sarawak and Sabah Shell operations, the use of 8 1/2" PDC bits in water based drilling fluids on rotary drilling con now be considered a proven application when drilling both clastics and carbonates. Only modest success has been achieved in 12 1/2" hole where tri-cone bit performance (Cost/ft) in generally softer clastic formations has proven more difficult to match with PDC bits. Introduction PDC (Stratapax) bit trials were initiated in Sarawak Shell Berhad/Sabah PDC (Stratapax) bit trials were initiated in Sarawak Shell Berhad/Sabah Shell Petroleum Company (SSB/SSPC) operations in July 1981. 30 runs in 12 1/4" size, 55 runs in 8 1/2" size and 4 runs in 6" size have been made. These trials involved a total of 57 bits of 14 different designs from 5 suppliers (Table 1). Bit prices range from US$15,000 to US$34,000 for 12 1/4" size and from US$10,000 to US$19,000 for 8 1/2" size. All bit runs are judged in terms of profitability (cost per foot comparison against rock bits). Smaller diameter bits have been more successful with 70% success rate in 8 1/2" size (all 6" bit runs are also successful). Cost per foot (standard cost per boot equation using bit cost and cost of rig time) reductions vary from 19% to 250% in 8 1/2" bit runs (See Figures 1 and 2). p. 12–1 p. 12–1