fax 01-972-952-9435. AbstractBit optimization played a key role in a recent drilling program by an oil company in its Pilot Production Drilling campaign in the Ruby Field Offshore Vietnam. Advancements in rollercone and PDC bit technology improved performance significantly. These advancements enabled the operator to save time on the 10 well plus 2-workover project and come in under budget. This paper documents the time savings and the development of the crucial roller cone bit technology.

The application of hybrid bits saves the operator drilling time by out-drilling conventional roller-cone and fixed-cutter bits in difficult, dense, tough and interbedded intervals. These intervals comprise interbedded sandstone, limestone, and siltstone down to depth of 12,500 to 13,500 ft. Operators who drilled these overbalanced wells typically used conventional roller-cone and fixed-cutter bits, depending on the area of the play. The roller-cone bits consistently drilled the entire interval, yet achieved slow penetration rates due to the lack of available weight. Fixed-cutter bits have been tested to achieve higher penetration rates. They drill faster than roller-cone bits with the available weight on bit but with higher drilling torque, close to the rig limitation. Fixed-cutter bits also experience dynamic dysfunctions that prematurely damage the bits, making it difficult to complete the entire interval. Extensive research, testing, and development have produced a hybrid bit that combines roller-cone and fixed-cutter elements to address these major challenges. The fixed-cutter elements make the bit more aggressive and provide higher penetration rates at low weight on bit. The roller-cone cutting elements drill through the harder part of the interbedded formation with much lower torque oscillations, making it easier to achieve the directional requirements, and reduce dynamic dysfunctions, improving the reliability of the bottomhole assembly and a better dull condition of the drill bit. This paper will present analysis of drilling data from the field to provide a detailed description of the operational challenges in this application by comparing the performance of roller-cone, fixed-cutter, and hybrid bits. After describing the planning and operational execution of drilling an 8.5-in. hole section with a hybrid bit in this challenging application, the paper concludes with a discussion of the technical and economical benefits and potential of this new technology.

This paper describes the successful development and application of a new low-friction flouropolymer-based coating applied to PDC bits to minimize and often prevent balling while drilling shale formations. Successful laboratory testing, the results of several field runs and one field case study will be presented. The rate of penetration is shown to more than double in certain cases resulting in significant savings to the operator. Introduction During development of the new coating process, full-sized commercial bits were tested in a laboratory under very controlled, simulated downhole conditions with and without the proprietary coating. The authors will present data from these laboratory tests, summarize several successful field runs and provide detailed results of one case study where a coated bit was used in the Tembungo B9 well for Petronas Carigali in Malaysia. This flouropolymer-based coating more than doubled the average penetration rate relative to standard PDC bits traditionally used to drill this hole section. The Malaysian case study will document that the coating prevented bit balling while drilling more than 1,400 feet. Although the coating was eroded at the conclusion of the run, the test was considered successful because of the significant improvement in average rate of penetration. Additionally, the authors document the economic savings of preventing downhole balling with PDC bits in water-based muds. Background PDC bits drilling with oil-based muds (OBM) or synthetic-based muds (SBM) have consistently set the performance benchmark for drilling shales, especially in deep, high pressured wells. The exceptions are areas where tightening environmental regulations, high risk of lost circulation and/or marginal project economics make use of OBM/SBM unattractive. These areas are growing and this has persuaded operators and service companies to invest considerable resources into trying to improve the performance of PDC bits with water-based muds.(1) The worldwide average penetration rate in deep, overpressured sections experienced by one major operator in 1997 was 12.7 feet per hour. Taking the figures for water-based mud alone, the average penetration rate was even lower. The combination of oil-based muds and PDC bits gave the best overall average rate of 17.3 feet per hour. It was recognized that if this performance could be achieved in all wells, the annual worldwide savings would exceed $500 million.(4) However, the use of oil-based muds is prohibited or restricted by environmental, safety, and other considerations in many parts of the world. Therefore, innovative methods must be found to solve the bit-balling problem, and increase drilling penetration rates with water-based muds. Causes and Prevention of Bit Balling When drilled with a PDC bit, rock tends to fail in shear, scraping cuttings off of the bottom of the borehole. PDC bit balling occurs when the chips do not separate themselves from the cutters and, instead, accumulate on the body of the bit.(5)(6) Historically there has been confusion about what causes drilling cuttings to agglomerate and attach themselves to the bit and bottom hole assembly.

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