NMDC - Non magnetized drill collar
1. Definition & Purpose
A Non-Magnetic Drill Collar (NMDC) is a specialized BHA component made from low-permeability alloys to create a magnetically neutral zone around MWD/LWD tools. Its primary functions are:
Isolate magnetic interference from standard steel components
Ensure accurate directional surveys (compass readings)
Maintain formation evaluation data integrity
2. Key Features & Advantages
| Feature | Benefit |
|---|---|
| Ultra-Low Permeability | <1.05 μ (vs 1.2+ μ in carbon steel) |
| High-Strength Alloys | Monel/K-500, Cu-Ni, or austenitic stainless steel |
| API-Compliant | Meets API 7-1 specs for dimensions/connections |
| Corrosion Resistant | Superior performance in H₂S/CO₂ environments |
3. Technical Specifications
Standards: API 7-1 + supplementary NMDC requirements
Sizes: 4¾" to 9½" OD (common directional drilling sizes)
Lengths: 30-31 ft (Range 2) or custom
Connections: NC46, NC50, 6⅝ FH typical
Permeability Testing: ASTM A342 (<1.05 μ verified)
4. Types of NMDCs
| Type | Material | Max Temp |
|---|---|---|
| Standard NMDC | Monel 400/K-500 | 400°F (204°C) |
| High-Temp NMDC | Custom austenitic alloys | 600°F (316°C) |
| Cost-Effective | 316L Stainless Steel | 300°F (149°C) |
