Enlarge hole in challenging deepwater formation

The operator wanted to run a 16-in liner at the desired wellbore depth while drilling in the deep waters on India's east coast. To run the liner, the operator needed to drill a 12 1/4-in pilot hole and enlarge it to 17 1/2 in while managing ECD in the soft claystone and abrasive sandstone formation with a UCS of 1,000 to 5,000 psi.

Underream using BHA with dual size reamers

Schlumberger analyzed drilling parameters, evaluated drilling mechanics, and compared BHA designs using the IDEAS platform and simulated each component of the BHA and drillstring using the i-DRILL design process. After determining the most stable BHA design and optimal parameters for the run, Schlumberger recommended using 11625 and 14250 Rhino XS hydraulically expandable reamers in tandem, placed near the bottom of the BHA.

In the first stage of the operation, the 11625 Rhino XS reamer was activated on surface to underream to 14 3/4 in. Then the 14250 Rhino XS reamer was activated in the second stage to underream to 17 ½-in. Finally, in the third stage, both reamers were activated to enlarge the section from 12 1/4 in to 17 1/2 in.

Eliminated two underreamer runs, saved 3 days

Using dual-size reamers on the same BHA enabled the operator to avoid making two underreamer runs, saving 3 days of rig time. Placement of the reamers near the bottom of the BHA eliminated rathole in the HPHT deepwater environment.

The operation marked the first time dual-size Rhino XS reamers were used on the same BHA to underream a wellbore. The 669-m section was the longest ever enlarged by dual reamers on a single run, and the ROP of 19 m/h was the highest-ever recorded for dual-size reamers.