New PDC Technology Solves Challenging Directional Application in Saudi Arabia

Abstract

Abstract Directionally drilling the 8–1/2" hole section in specific areas of Saudi Arabia is particularly challenging due to a complex stratigraphic section that consists of soft, dense limestone and anhydrite with tough bands of hard stringers. Historically, roller cone bits with tungsten carbide inserts (TCI) have dominated the 8–1/2" application due to proficient steerability and ability to consistently achieve the required build rates in the soft limestone. However, multiple runs are required to finish the entire section. Conversely, Polycrystalline Diamond Compact (PDC) technology increased ROP but lacked consistency due to fluctuations in reactive torque that resulted in poor tool face control and inconsistent build-up rates relative to roller cone bits. Saudi Aramco determined to efficiently drill the section in one run and meet performance and directional requirements would require new PDC technology. To address this challenge, Saudi Aramco and a service company organized an integrated cross-functional team composed of engineers from both companies to aggressively seek new steerable PDC technology to drill the curved section with controllable torque response and consistent directional behavior while achieving the full penetration rate advantages of PDC bits. The team analyzed the drilling operation from virtually every perspective using numerical models, laboratory drilling tests, and field testing. The key to the PDC solution was the team process that identified the relevant drilling problems and performance requirements in order to develop the needed technology. The team identified that poor tool face control in the soft limestone and cutter damage due to vibration problems were the primary obstacles in achieving performance goals. The solution was a PDC design with a new steerable concept that provided exceptional tool face control without sacrificing ROP in addition to improved stability and new cutter technology for prolonged bit life. After 15 bit runs, the team reduced drilling cost by $17.55 per foot for a total savings of $857,476 over 48,871 ft and 1880.5 drilling hours. The average ROP for the section increased from 22.47 ft/hr with standard PDC bits to 26 ft/hr with the new PDC technology. The current ROP record stands at 42.02 ft/hr with the single run record footage standing at 6,229 ft. Introduction Saudi Aramco and bit manufacturer have been working together for over 50 years. Most recently they have been optimizing roller cone technology for use in the 8–1/2" curved interval, improving cutting structure and metal face sealed bearing performance. Despite advances in directional drilling technology and more powerful positive displacement motors (PDM), even as recently as late 2001, IADC code 537 roller cone bits could not finish the hole section in a single run. PDC bits showed promising results but were inconsistent in holding tool-face control, delivering the required build-up rates and had limited bit life due to downhole vibration which required the use of multiple PDC bits. The lithology for this section is predominantly carbonates with some shale interbeds. The well profiles change depending on the well-to-target location with some wells requiring a complex three-dimensional profile. In the build section of two dimensional well profiles, many PDC runs were successful at improving the footage drilled over roller cone bits; but as more complex wells were drilled, tool face control and achieving the required build-up rates were the major obstacles to standard PDC bits. Seeing an opportunity to reduce drilling costs, engineers from Saudi Aramco and bit supplier developed a new technology for steerable PDC bits through an open and cooperative process.