Hard formation caused premature bit damage

An operator in Russia's Garshinksoe field was drilling an S-type well through a hard, interbedded limestone and dolomite formation. With compressive strength ranging from 82.7 to 172.4 MPa [12,000 to 25,000 psi], abrasive sandstone and chert inclusions, and lost circulation zones, this section required five to six bits to reach total depth. While an average ROP of 9 m/h [30 ft/h] was achieved, the operator wanted to maintain penetration rates while reducing bit damage and the number of runs.

Advanced bits with unique-geometry cutting elements improve footage and ROP

Schlumberger performed a detailed offset analysis to look at application-specific data and identify optimal drilling technologies. After using the DBOS drillbit optimization system to study offset wells, Schlumberger determined the primary determinant of success was cutting structure durability.The DBOS system analysis revealed that the hard limestone and dolomitic stringers caused impact damage to the cutting structure and reduced ROP.

To maximize footage drilled and ROP in the top interval, Schlumberger recommended using the StingBlade bit. Stinger conical diamond elements apply a significantly higher concentrated point load on the rock. In addition, the elements' thicker diamond table minimizes abrasive wear and impact damage. For the middle and bottom interval, Schlumberger recommended the AxeBlade bit for high steerability and better frontal impact resistance.

Operator drilled section 4.1 d faster than average

The operator deployed the StingBlade and AxeBlade bits in two wells, successfully drilling the troublesome section in record time and setting multiple field records. The operator drilled the section in 9.1 d and 9.7 d, respectively, with an average ROP of 12.7 m/h [41.7 ft/h]—exceeding average field ROP by 40%.

The advanced bits drilled the section in just two runs, eliminating three runs and saving up to 4.1 d of rig time. In addition, the operator drilled 1,709 m [5,607 ft] from the shoe—a 5% improvement over the previous footage record in the field. These drilling efficiencies reduced costs by USD 45,700 compared with offset wells drilled with conventional PDC bits.