SLB improved drilling performance in long 12¼ tangent section of wet, offshore Oman using Neyrfor Traditional™ standard turbodrill.

Improve drilling performance in long 12¼-in well section

An operator planned to drill a 12¼-in section of an appraisal well in offshore Oman, which had a 2,300 m long tangent to be held at 42.6° inclination while crossing two formations—a struggle to drill in previous wells. The upper formation was mainly claystone, interbedded with thin limestone stringers; the lower formation was shale interbedded with limestone. The unconfined compressive strength of both formations was between 15,000 and 20,000 psi.

A variety of BHAs were used to drill the 12¼-in sections of previous wells—PDC and TCI bits with positive displacement motors and rotary steerable systems (RSS)—but none proved satisfactory. Because the average ROP was frequently below 2 m/h, the operator wanted to improve drilling performance.

Increase ROP in hard formation with turbodrill and hybrid bit

SLB used 9½ in T112HF steerable Neyrfor Traditional turbodrill with 12¼ impregnated hybrid bit. We drilled 250 m at average ROP of 4.7 m/h, maintained planned well trajectory throughout long section, and increased ROP 88%, saving approximately USD 4 million.

SLB recommended using a 9½-in T112HF steerable Neyrfor Traditional standard turbodrill to drive an impregnated hybrid bit with 16-mm PDC cutters. This combination, which was selected based on hydraulic calculations, significantly increased ROP and reduced drilling time. The bent housing on the turbodrill’s bearing section was set at 0.75° to perform any directional work required to maintain the planned trajectory, and the turbodrill was configured with a 12⅛-in lower bearing stabilizer (LBS) and a 12-in midbody stabilizer (MBS) to hold inclination and azimuth. In addition, there was an 11¾-in stabilizer on the MWD tool above the turbodrill.

Increased ROP and reduced drilling time, saving USD 4 million

The steerable Neyrfor Traditional turbodrill and impregnated hybrid bit achieved an average ROP of 4.7 m/h in the hardest interval of the 12¼-in section, which is 88% higher than the 2.5 m/h average ROP from the RSS and PDC bit in the previous interval. The performance improvement in the 250-m interval saved the operator nearly two days of drilling time and approximately USD 4 million.

The first 212 m of the 12¼-in section, from 3,211 m to 3,423 m MD, were drilled at an average ROP of 2.5 m/h using a BHA with a PDC bit and RSS. At that point, inclination was 45.83° and azimuth was 221.1°. A trip was then made to change to a BHA with the steerable turbodrill and hybrid bit to drill the claystone and limestone formation—considered the section’s hardest interval.

The turbodrill BHA then drilled 250 m through the hard upper formation at an average ROP of 4.7 m/h. Throughout the run, inclination and azimuth were held at 45.79° and 222.36°, respectively, per the well plan, with just 33 m spent sliding. After reaching the lower formation at 3,673 m MD, a trip was made to change back to the BHA with the RSS and PDC bit because the formation was softer than the upper one.