Roller cone bits have dominated the 8–1/2" steerable application in Abu Dhabi due to their proficient steerability, consistently achieving the required build rates in the soft Nahr Umr shale. In the vertical section, PDC bits often achieve up to four times the penetration rates of TCI bits. However, directional performance when using PDC bits to build angle was compromised by fluctuations in reactive torque resulting in poor tool face control and inconsistent build up rates. The overall result was poor penetration rate and performance compared to roller cone bits. The operator and a service company utilized a new design process and cross functional team approach 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 advantage of PDC bits. This process was complemented by the Well Delivery Limit process (WDL) that was already established by the operator that focused on delivering high value wells with significantly reduced costs. The team analyzed the drilling operations 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. After 30 bit runs from November 2001 to June 2002, the team reduced drilling costs by $44.26 per foot for a total savings of $3,792,367 over 85,682 ft and 2,386 drilling hours. The average ROP for the section doubled from 18 ft/hr with TCI bits to 36 ft/hr. The current ROP record stands at 60 ft/hr over a 3,169 ft interval. Introduction The operator and bit manufacturer have a history of joint optimization of roller cone technology in this 8–1/2" interval, improving cutting structure and metal face sealed bearing performance. The operator has documented these achievements, along with two failed attempts to drill wells with PDC bits.1 Despite advances in directional drilling technology and more powerful positive displacement motors (PDM), even as recently as late 2001, IADC code 517 roller cone bits were the only technology that could provide both tool-face control and build up rates required for the well plans. The lithology for this section consists of short section of limestone, followed by long section of soft shale to the landing point in a limestone reservoir. All PDC attempts failed to achieve any significant drilling improvements because of poor tool face control and inadequate build rates through the soft shale. Seeing an opportunity to reduce drilling costs, engineers from the operator, bit supplier and motor supplier developed a new technology for steerable PDC bits through an open and cooperative process. Well Plan The 8–1/2" interval starts at approximately 6,600 ft at the bottom of a limestone interval where unconfined compressive strength (UCS) ranges between 9 and 21 ksi. At approximately 7,400 ft, a 3 to 5 ksi UCS shale is encountered which extends to the top of the reservoir at 8,100 ft. Almost half of the directional work takes place in the soft shale before the reservoir is penetrated at around 40 degrees of inclination. The limestone reservoir features alternating soft and hard layers, with the softer rock around 9 ksi UCS and the firmer rock 15 to 26 ksi UCS. Figure 1 shows a plot of the rock type and compressive strength versus depth while Figure 2 shows two typical well plans. Directional work continues until the well is horizontal and measured depths often extend to 9,500'.

fax 01-972-952-9435. AbstractRoller cone bits have dominated the 8-1/2" steerable application in Abu Dhabi due to their proficient steerability, consistently achieving the required build rates in the soft Nahr Umr shale. In the vertical section, PDC bits often achieve up to four times the penetration rates of TCI bits. However, directional performance when using PDC bits to build angle was compromised by fluctuations in reactive torque resulting in poor tool face control and inconsistent build up rates. The overall result was poor penetration rate and performance compared to roller cone bits. The operator and a service company utilized a new design process and cross functional team approach 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 advantage of PDC bits. This process was complemented by the Well Delivery Limit process (WDL) that was already established by the operator that focused on delivering high value wells with significantly reduced costs. The team analyzed the drilling operations 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. After 30 bit runs from November 2001 to June 2002, the team reduced drilling costs by $44.26 per foot for a total savings of $3,792,367 over 85,682 ft and 2,386 drilling hours. The average ROP for the section doubled from 18 ft/hr with TCI bits to 36 ft/hr. The current ROP record stands at 60 ft/hr over a 3,169 ft interval.

fax 01-972-952-9435. AbstractDirectionally drilling the 8-½" 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.