Breaking Through: Sidetracking from the Low Side of a Horizontal Wellbore

By Tejas Ghegadmal

The Challenge: Navigating a Crowded Subsurface

In mature oil and gas fields, operators often face a complex web of existing wellbores—especially in high-density development zones or unconventional plays. Drilling a new branch (sidetrack) from a horizontal or near-horizontal well is no small feat when the risk of intersecting existing wellbores—both known and unknown—is high.

Even with today’s high-precision rotary steerable systems, steering a sidetrack cleanly through this dense subsurface "traffic" can be technically risky and prohibitively expensive.

But what if you could drastically reduce the need for steering altogether?

A Smarter Approach: Exiting from the Low Side

One counterintuitive yet effective strategy is to initiate the sidetrack from the low side of the horizontal wellbore. Why?

• Most pre-existing wellbores in horizontal zones tend to cluster on the high side, either due to natural drilling tendencies or past sidetracks.

• Exiting from the low side naturally guides the new wellbore away from the crowded upper half, minimizing collision risk.

• It also simplifies trajectory control, reducing reliance on active steering systems.

However, low-side exits introduce their own mechanical complications—specifically in the deployment and geometry of the whipstock ramp.

The Sagging Whipstock Problem in Horizontal Wells

The whipstock ramp is a key component in sidetracking—it’s a cased hole deflector tool that guides the mill during window cutting. In a vertical or moderately inclined well, it behaves predictably. But in a fully horizontal well, the whipstock sags under its own weight.

What happens?

• Gravity causes the top of the whipstock to collapse against the low side of the wellbore.

• This obstructs the milling assembly, leading to poor window geometry, cutter damage, or even tool sticking.

• Worse still, it impedes the drilling BHA after the window is cut, increasing friction, vibration, or complete failure to exit.

Engineering a Solution: Rotational Anchoring for Whipstock Tilt Control

To overcome this, a specialized anchoring system was designed—an innovative enhancement to the standard whipstock anchor.

Key capabilities:

• The anchor doesn’t just lock the whipstock axially—it can rotate it slightly around its base, like a controlled hinge.

• This controlled rotation tilts the top of the whipstock upward, away from the low side.

• The system allows the whipstock to be angled toward the high side, creating ample clearance for both the milling and drilling assemblies.

Think of it as "reorienting the ramp" in a tunnel: instead of lying flat and blocking the way, it’s subtly lifted and aligned to optimize flow.

Operational Impact

This rotational anchor-driven tilt mechanism:

• ✅ Eliminates wellbore obstruction caused by whipstock sagging.

• ✅ Enables clean, reliable low-side exits in horizontal wells.

• ✅ Reduces risk of wellbore collision in high-density fields.

• ✅ Improves mill and BHA run reliability, reducing non-productive time.

• ✅ Makes sidetracking feasible without complex steering systems.

The result? Operators can unlock untapped reservoir zones even in crowded well fields—safely, efficiently, and with higher confidence.

Conclusion

Sidetracking from the low side of a horizontal well might seem unconventional, but with the right mechanical solution—like a laterally adjustable whipstock anchor—it becomes not just possible, but optimal.

This kind of precision mechanical innovation reflects the future of downhole tools: simplify the path, reduce the risk, and enable smarter decisions underground.

Have questions about sidetracking? Let’s talk. Reach out via E-mail or connect on LinkedIn.