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Technical Paper: Solving Deep 22-in Carbonate Drilling Challenges in Northern Kuwait

Society: SPE
Paper Number: 151789
Presentation Date: 2012
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Abstract

The operator must drill a deep, vertical 22-in hole section in a high-pressure, high-temperature (HPHT) environment to efficiently tap Jurassic reserves in the North Kuwait gas fields. The borehole starts at approximately 6050 ft and continues to 9350 ft. Interbedded lithologies encountered include carbonates, sandstones and shales with compressive strength between 6000-25,000 psi. The section can take 350 hrs to reach total depth (TD). 

Historically, the section has been drilled with PDC and rollercone TCI bits. TCI had unacceptable ROP with short life requiring multiple runs. Frictional heat in Mutriba was causing inserts to crack/chip leading to total failure. The abrasive Burgan and Zubair with pyrite were causing extensive insert wear. PDC bits could deliver acceptable ROP, but inconsistent run lengths and vibration induced impact damage were driving up field development costs. Neither bit type could consistently complete the hole section in one run.

To solve the problem, a forensic investigation of TCI bearing, carbide materials, and insert shapes was conducted. The study resulted in new impact resistant carbide grades, and unique insert geometries specifically tailored for Middle East carbonate/sandstone drilling. A dynamic twin-sealing system ensures long bearing life. The design was tailored to maximize ROP while retaining a high level of cutting structure durability. The bit was run on RA-414 with outstanding results, setting a new Kuwaiti 22-in record, drilling 3311 ft in 335 hours (9.8 ft/hr) reaching deep into abrasive Zubair sandstone. It is the most footage drilled by any bit type in the application and the first TCI to penetrate Zubair. It was dull graded 3-5 with all three seals effective in spite of turning two million revolutions. It eliminated multiple bits/trips to complete the hole section reducing rig-time expenditures, bit spend and the expense of a motor required for PDC. With additional modifications, it's probable the bit will drill the section in one run in the near future.

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