New Slimhole Technology Maximizes Productivity in Middle East Horizontal Drilling Programs

Abstract

Abstract Numerous operators are using advanced slimhole drilling technologies in development programs throughout the Middle East. These programs involve new and re-entry wells with long horizontal sections, typically 6" or 6–1/8" in diameter. Rollercone bits are often used in these applications because of their overall robustness, superior directional characteristics and predictable sidecutting ability. Slimhole PDC bits are run when possible, but problems with high torque, toolface control and drillstring dynamics often prevent their use. Traditionally, operators have been reluctant to attempt long runs with slimhole rollercone bits due to the potential for lost cones after undetected seal failures. An innovative new metal sealed slimhole rollercone bit was recently developed. The downsized primary metal seal has proven its ability to significantly improve bearing life and reliability. The longevity of the new bearing has allowed operators to gain considerable confidence, which has translated into more on-bottom drilling hours and a high TD rate. The metal seal is especially useful on high speed (200 - 450 rpm) steerable motor assemblies, where elastomer seals wear at an accelerated rate. The new bits are achieving over 1100 krevs at 80% reliability throughout the Middle East, while conventional elastomer sealed bits achieve only 600 krevs at 80% reliability in head to head comparisons. In Abu Dhabi, the new bits are used to drill out from 7" casing, then geosteer horizontally for 4000ft+ of limestone with a UCS between 5,000 psi and 15,000 psi. The authors will document significant cost reductions through improved bit performance from several years of drilling in active fields in UAE (2003 - Aug 2004). The primary advantage of utilizing the new slimhole bit is they can drill the horizontal section in one fast run. Historically, it takes two elastomer sealed bits to complete the hole section. Reduction in drilling time due to higher ROP and elimination of tripping for a new bit has led to significant savings in rig time while minimizing formation damage by reducing the exposure of reservoir formations to drilling fluids. Introduction Historically, TCI bits with elastomer bearing seals (ES) were used to drill the slimhole sections in 6" size in Abu Dhabi. In other Middle East countries, 6–1/8" is the most commonly used bit size. Abu Dhabi Typically, the 6" hole section is drilled horizontally through the limestone reservoir (Shuaiba or Thammama group), sometimes crossing from zone to zone through the dense limestone. The reservoir tolerance set by operator is +/− 3 ft, but can allow +/− 5 ft; this tight tolerance requires the directional driller to geosteer in the reservoir section to keep the well on target. The reservoir section is porous and fractured limestone, with unconfined compressive strength (UCS) below 5 kpsi. The cap rock (dense limestone) ranges between 12 and 15 kpsi. The section length typically varies between 3000 ft to 4000 ft depending on the well, and sometimes extends to 6000 ft. Historically, two elastomer sealed IADC 4–3-7 type bits were required to drill the 4000 ft sections due to hours on the bit. Instantaneous ROP's are above 150 ft/hr and are at times limited by data capture speed of the MWD system. The additional trips for bit change-out not only cost rig time but also increase the exposure time of the reservoir to the drilling fluids, which can result in greater formation damage.