Allegro CD Service: Improving Well Economics

Published: 11/11/2021

Close up of the blade with bits and a digital overlay
Allegro CD Service: Improving Well Economics
Directional casing-while-drilling service

Allegro CD directional casing-while-drilling service is about improving the economics of well construction. It’s about increasing your drilling efficiency, strengthening your wellbore, and enhancing hole cleaning to eliminate borehole-related problems that compromise the integrity of your well as you drill to TD. It’s about the time exposure and duration between drilling the hole and casing it, whether related to different pressure gradient, unstable formation, losses or gains, and challenging directional profiles. And the longer the hole or section’s exposed and uncased, the higher the chance of NPT, delays, and unplanned costs.

Here’s how Allegro CD service addresses all that. The BHA is anchored to the casing through the drill-lock assembly that also enables the BHA to be unlocked and locked multiple times for tripping out. We use either a mud motor or a rotary steerable system in the casing string to rotate the bit and reamer to drill the interval. The narrow annulus creates a high annular velocity for better hole cleaning and, as the casing rotates, enables the casing to grind and smear cuttings into the borehole wall, forming a plastering effect, which helps minimize fluid invasion into the formation, improve wellbore stability, and provide better cement placement.

The BHA and casing are steered through the curve and tangent into the lateral interval to TD as with any other drillstring. After the annulus is circulated clean, a release tool unlocks the BHA from the casing. Once casing is run over the BHA to secure the underreamed hole, the BHA is pulled to surface, eliminating stuck pipe because of key seating, bore instability, or differential sticking. The cement head is then mated to the casing string, and the well is conditioned for pumping cement downhole. The cement plug is run in hole to the shoe, where it locks and seals to prevent cement U-tube effect. At this point, the bit drills out the plug without a dedicated bit run.

Allegro CD directional casing-while-drilling service from Schlumberger.

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