Through tubing reentry drilling (3⅝") operations were first commenced in Saudi Arabia in 2008. Since then the application has proven to be an efficient and reservoir friendly method of reentry drilling. Old vertical and sometimes deviated candidate wells are screened and worked over bysetting a through tubing whipstock in the 4½", 5½" and 7" casings then exiting in a 3⅝" hole size. A curve section is then drilled at 20° to 35°/100 ft build up rate (BUR) and subsequently, lateral sections of 2,000 to 3,000 ft are drilled in the reservoir.

Despite the good learning curve, certain technical challenges are limiting the operating envelope of 3⅝" through tubing re-entry drilling (TTRD). Some of these challenges are: surface setup and pressure deployment, inefficient tool face control, vibration, releasing a stuck bottom-hole assembly (BHA), etc. Other challenges related to drilling snadestone reservoirs.

Keeping these challenges in mind, Saudi Aramco and Schlumberger (SLB) embarked on a project to develop a new drilling system, which would prevent and mitigate the risks highlighted above and allow safe application of 3⅝" TTRD to areas and fields where it was previously not practicable. This new drilling system was successfully deployed to the field in June 2012.

The paper will cover some of the key features of the new drilling system, which were proven during the first job.

Shorter BHA coupled with a customized tower, thereby eliminating the need for pressure deployment, greatly enhances safety and efficiency.

  1. Secondary release mechanism allowing for 90% recovery of BHA in case of a stuck bit.

  2. High precision and variable speed orienting system for more precise tool face control.

  3. A single ball valve in the upper BHA eliminates the need to bleed off the coil tubing (CT) pressure during deployment operations when drilling with nitrogen, saving time and money.

  4. Ultra-sensitive vibration sensors coupled with a 2-3 second update rate allows for quick identification of performance drilling motor (PDM) or turbine stalls.

  5. Coupled with high buildup rate turbodrills, the new drilling system is capable of drilling tight curves and laterals through compact and abrasive pre-Khuff sandstones at more than double the rate of penetration (ROP) previously possible with PDMs in a reduced number of trips.

Wider deployment of this new drilling system would potentially unlock the true potential of the tight and abrasive pre-Khuff sandstone reservoir.

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