The Relationship Between Drill Collar Specifications and Weight

The drill collar, located at the bottom of the drill string, is a key component of the lower drill string assembly. Its primary characteristics are its thick wall thickness (typically 38-53 mm, equivalent to 4-6 times the drill pipe wall thickness), resulting in high resistance and rigidity.

Material and Structure:
The mainstream material is AISI4145H chromium-molybdenum alloy steel, which achieves a Brinell hardness of 285-341 after heat treatment.
Drill collars are categorized by structure into three types: solid drill collars, spiral drill collars, and non-magnetic drill collars. Spiral drill collars utilize a spiral groove design to reduce the contact area with the wellbore wall, thereby minimizing the risk of sticking due to differential pressure.

Basic Drill Collar Parameters:
API drill collar specifications include:
(a) Size (OD): 3-1/8" to 11";
(b) Type: Round, Helical, Non-Magnetic;
(c) Drill Collar Specifications: API Spec 7-1, API Spec 7-2, API RP 7G;
(d) Other products to meet the needs of deep well and harsh drilling environments.

Relationship between Drill Collar Diameter and Weight:
Drill collars are essential tools in oil drilling, and their weight and diameter directly impact drilling efficiency. The larger the diameter of a drill collar, the heavier it typically is. Common drill collar diameters range from 4 inches to 9 inches, corresponding to weights per meter ranging from 80 kg to 350 kg. A 178mm drill collar, with a diameter of approximately 7 inches, typically weighs around 1.5 tons, making it a medium-sized tool suitable for most conventional drilling operations.

Drill Collar Specifications and Weights:
Drill collar weight increases with outer diameter. Common specifications and weights are as follows (based on standard lengths of 9-12 meters):

1. Small Drill Collar: 79mm (3-1/8 inches) outer diameter, weight approximately 0.3 tons; 89mm (3-1/2 inches) outer diameter, weight approximately 0.4 tons.

2. Medium Drill Collar: 159mm (6-1/4 inches) outer diameter, weight approximately 1.2 tons; 165mm (6-1/2 inches) outer diameter, weight approximately 1.3 tons; 178mm (7 inches) outer diameter, weight approximately 1.6 tons.

3. Large Drill Collar: 203mm (8 inches) outer diameter, weight approximately 2.2 tons; 229mm (9 inches) outer diameter, weight approximately 2.8 tons; 254mm (10 inches) outer diameter, weight approximately 3.5 tons.

Main Functions of the Drill Collar:
(1) Apply drilling pressure to the drill bit;
(2) Ensure the necessary strength under compression conditions;
(3) Reduce the vibration, swing, and jump of the drill bit, so that the drill bit can operate smoothly;
(4) Control the well inclination.

Read more: Difference between Drill Pipe and Drill Collar