Packed BHA (Bottom Hole Assembly)
A Packed BHA is a directional drilling BHA designed to maintain inclination and drill a straight hole with minimal tendency to build or drop angle.
Configuration
Typically consists of:
- Bit
- Near-bit stabilizer
- String stabilizer(s)
- Drill collars
- MWD/LWD tools (if used)
The stabilizers are placed close together, making the BHA “packed” and stiff.
Typical Layout
Bit → Near-Bit Stabilizer → Drill Collar → String Stabilizer → Drill Collar → String Stabilizer → Drill Collars
Purpose
- Hold inclination (tangent section).
- Drill a smoother wellbore.
- Reduce doglegs.
- Improve directional control.
- Minimize unwanted build or drop tendency.
How it Works
Because stabilizers closely support the drill collars, the BHA remains rigid and centered in the hole. This reduces bending forces that would otherwise cause the well to build or drop angle.
Advantages
✔ Maintains planned trajectory.
✔ Low dogleg severity (DLS).
✔ Better hole quality.
✔ Reduced tortuosity.
✔ Good for tangent sections.
Disadvantages
✘ Difficult to build angle.
✘ Less aggressive directional response.
✘ More drag in some formations.
Packed BHA vs Pendulum BHA
| Feature | Packed BHA | Pendulum BHA |
|---|---|---|
| Tendency | Hold angle | Drop angle |
| Stabilizers | Close to bit and packed | First stabilizer far from bit |
| Directional effect | Neutral/straight | Decrease inclination |
| Application | Tangent section | Angle reduction |
Interview Question
Q: When would you use a packed BHA?
A: A packed BHA is used when we want to maintain the current inclination and azimuth, such as in a tangent section of a directional well. The closely spaced stabilizers make the assembly stiff and reduce the tendency to build or drop angle.
For directional drilling interviews, remember the three classic BHAs:
- Packed BHA → Hold inclination.
- Pendulum BHA → Drop inclination.
- Fulcrum BHA → Build inclination.
