Drill collar
1. Definition & Purpose
A Drill Collar is a thick-walled, heavy tubular component of the Bottom Hole Assembly (BHA) that provides:
Weight on Bit (WOB) for efficient drilling
Stiffness to prevent buckling and maintain wellbore trajectory
Stability to reduce vibration and improve drilling accuracy
2. Key Features & Advantages
| Feature | Benefit |
|---|---|
| High Linear Weight | 4-6x heavier than drill pipe for optimal WOB |
| Rigid Structure | Minimizes deflection in directional drilling |
| Tool Joint Connections | API-registered threads (e.g., NC, FH, IF) |
| Material Options | Non-magnetic variants for MWD applications |
3. Technical Specifications
Standards: API 7-1 / ISO 10424-1
Sizes: 3¼" to 11" OD (common range)
Lengths: 30-32 ft (Range 2)
Weights: 50-220 lbs/ft
Materials:
AISI 4145H (standard)
Non-magnetic (Monel, Cu-Ni for MWD)
4. Types of Drill Collars
| Type | Purpose |
|---|---|
| Standard | General drilling applications |
| Spiral | Reduces wall contact (prevents differential sticking) |
| Non-Magnetic | MWD/LWD environment isolation |
| Square | Reaming/stabilization in hard formations |
