HolePlan™ is a trademark of Hole Plan Ltd. All software code and 3D visualisation logic are protected under the International Copyright Law. This software is an independent engineering tool and is not affiliated with any hardware manufacturer.
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In directional drilling, the "Dogleg Severity" (DLS) is a critical metric that measures the curvature or change in direction of the borehole over a specific distance (typically degrees per 30 meters or 100 feet). Navigating a drill string through sharp bends can lead to catastrophic equipment failure if not managed correctly.
To streamline the deviation process, trajectories are analysed through a real-time visual feedback system. This system correlates curvature intensity with the Canadian Diamond Drilling Association (CDDA) recommended maximums to ensure bending stress remains below 83 MPa (12,000 psi).
| HolePlan Zone | DLS Range (per 30m / 100ft) | CDDA Max Limit (Recommended) | Recommended Rod Size | Risk Assessment |
|---|---|---|---|---|
| Yellow | 4° – 6° | HQ™ (Max 8.0°) | HQ / HW-Sized Rods | Optimal: Minimizes wear while allowing steering for larger rods. |
| Orange | 7° – 12° | NQ™ (Max 10.0°) | NQ / NW-Sized Rods | Standard: The "sweet spot" for mid-sized directional control. |
| Orange | 11° – 13° | BQ™ (Max 12.0°) | BQ / BW-Sized Rods | High Stress: Reaching the fatigue limit for small-diameter rods. |
| Red | > 14° | Exceeds All | Dangerous | Critical: Risk of "twist-offs" and rapid joint thinning. |
Technical Note: Note that as rod diameter increases, the allowable DLS decreases. An HQ rod is significantly stiffer than a BQ rod, therefore, a 12° per 30m (100ft) bend that is "Safe" for a BQ rod would be "Critical" for an HQ rod.
All technical data and safety limits within HolePlan are based on the specifications provided by leading drill pipe manufacturers, such as Boart Longyear, and the collective expertise of experienced directional drilling field engineers.
Failure to mitigate high-DLS segments results in "Hidden Costs" that impact both the mechanical integrity of the drill string and the project's bottom line.
When a drill rod rotates within a sharp bend, it undergoes rapid cycles of tension and compression. Exceeding the material's endurance limit leads to cumulative metal fatigue. If unmanaged, this results in a "downhole twist-off," necessitating expensive and time-consuming fishing operations.
High curvature (DLS above 14°) acts as a mechanical brake. As the trajectory enters the "Red Zone," the side-force pushing the drill string against the borehole wall increases exponentially.
Friction requires the rig to output significantly more torque to maintain rotation.
To overcome this friction, engine load increases, leading to a direct spike in fuel costs. Smooth trajectories in the Yellow/Orange zones are essential for fuel-efficient operations.
The tool joints are the thickest part of the drill string and take the brunt of the friction in high-DLS areas. This leads to accelerated thinning of the pipe walls and can result in fluid leaks or stripped threads, necessitating expensive rod replacements.
If a trajectory indicates Red Zone segments, the following mitigation steps are recommended by technical experts:
Optimizing the planned trajectory is based on utilizing a lower DLS during the design phase. While this results in a longer directional drilling section, it effectively "smooths" the curve into the Yellow or Orange zones, ensuring the trajectory remains within safe mechanical limits.
If a high DLS section is encountered, we recommend reaming the "Red Zone" section with a brand-new or oversized reamer to "kill the bend." If the curvature is too high, the section must be cut out and the directional drilling section re-drilled with an adjusted DLS.
Proactively managing high-curvature zones protects your equipment, lowers your fuel costs, and ensures a more successful drilling program.
Technical Note: Note that as rod diameter increases, the allowable DLS decreases. An HQ rod is significantly stiffer than a BQ rod, therefore, a 12° per 30m (100ft) bend that is "Safe" for a BQ rod would be "Critical" for an HQ rod.
The technical thresholds and risk zones utilized within our software are anchored in the following industry-recognized standards and engineering guidelines.
The Lubinski Formula for Bending Stress (Sᵦ):
Sᵦ = (E · D · θ) / (2 · L)
Where E is Young's Modulus, D is the rod diameter, and θ is the change in angle over length L.
