drilling · directional
Build-and-Hold Trajectory Planning
R = 1718.87/BUR; HD = R(1−cosθ); TVDgain = R sinθ
click formula to derive ↑
Inputs
°/100ft
°
Description
Plans the simplest directional trajectory type — a build section from vertical (or an existing low angle) to a target inclination, followed by a straight hold. Computes the radius of curvature implied by the chosen build rate and the resulting horizontal displacement and TVD gained within the curve itself.
Variables
| Symbol | Unit | Description |
|---|---|---|
| R | ft | Radius of Curvature |
| HD | ft | Horizontal Displacement |
| ΔTVD | ft | TVD Gained in Curve |
| BUR | °/100ft | Planned build rate for the curve section. Conventional motor/RSS curves typically run 2-6°/100ft; short-radius curves can exceed 15°/100ft. |
| θ | ° | Inclination to be held after the build section ends — 90° for a horizontal lateral, less for a deviated straight hold. |
Assumptions
- Build rate is held constant throughout the curve (no build-rate changes within the section being planned)
- The curve starts from zero inclination — for a build section starting from a non-zero kick-off inclination, treat θ as the incremental inclination change
- Single-plane curve (build only, no turn) — for a build-and-turn trajectory, use the full minimum curvature method instead
Limitations
- Real BHAs rarely hold a perfectly constant build rate — actual wells require survey-based correction during execution
- Does not account for formation tendency (walk/drift) that can add an unplanned turn component to a nominally build-only section
- For trajectories with both build and turn, this single-plane model understates the true 3D radius of curvature — use min_curvature_survey on actual survey data instead
Use Cases
- → Kick-off point (KOP) selection: Work backward from a target inclination and horizontal displacement requirement to determine where the build section must start.
- → Curve section BHA selection: Match the planned build rate to motor bend setting or RSS build-rate capability before spudding the curve.
- → Quick trajectory screening: Estimate horizontal reach and TVD use of a simple build-and-hold design before running full 3D well-planning software.
Related Calculations
Region Notes
Permian Basin
Typical Wolfcamp/Bone Spring curve designs use 8-10°/100ft build rates over a ~900-1,100 ft curve to land at 90° inclination for a 2-mile lateral.
Bakken
Tight kick-off windows above the Three Forks often require build rates of 10-12°/100ft to reach horizontal within the available curve interval.
Eagle Ford
Standard curve designs target 8-9°/100ft build rates; short-radius designs exceeding 15°/100ft are used where surface location constraints are severe.
Global
Build rates below 6°/100ft are considered conventional (standard motor/RSS BHAs); rates above ~10°/100ft are short-radius designs requiring specialized BHAs and casing wear management.
References
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