What is the Wireline Double Tube Core Barrel Assembly?

The Double Tube Core Barrel Assembly in wireline core drilling consists of two primary components:

• Outer Tube Assembly: Includes the spring stopper, spring housing, expandable bit, outer tube, and drill bit.
• Inner Tube Assembly: Composed of the core basket, spring clamp, adjustment mechanism, suspension assembly, and core blockage alarm system.

Together, they ensure smooth operation, accurate core retrieval, and reliable performance in challenging drilling environments.

Key Components and Functions:

1. Locking Coupling Mechanism
Comprised of the Locking Coupling, latch, and spring, this system ensures that the inner tube assembly can be lowered vertically along the drill rod while maintaining contact with the wellbore walls. At the point of the spring housing, the latch is held open by the spring, restricting further expansion. The Locking Coupling prevents upward movement, and the latch is actuated by the puller fork during drilling to avoid wear and to enable rotational movement of the inner tube.

2. Landing System
The suspension mechanism involves the landing shoulder (inner tube) and the landing ring (outer tube). The suspension ring is slightly larger in diameter than the seat ring (typically by 0.5–1 mm), ensuring a clean and secure seating. This design prevents damage to the core basket and maintains optimal single-action performance.

3. Single-Action Mechanism
This system, composed of two thrust bearings, is designed to prevent the inner tube from rotating during drilling operations. It ensures that the inner tube remains stationary while the outer tube rotates, thereby improving core alignment and reducing wear on internal components.

4. Adjustment Mechanism
The adjustment mechanism includes the adjustment nut, adjustment coupling, and inner tube. During installation, if there is an improper gap between the core lifter and the drill bit, the system can be fine-tuned by adjusting the distance between the coupling and the spring sleeve. This allows for a precise gap adjustment of up to 0.3 mm, ensuring compatibility and optimal performance.

5. Positioning Alarm System
This is a critical component that alerts operators when the inner tube reaches the designated drilling position. Once the inner tube is lowered to the correct depth, the landing shoulder rests on the landing ring, blocking the flushing fluid passage. The fluid then is forced to change direction, overcoming the spring pressure and pushing the valve plug (steel ball) downward, thereby opening the flushing path. This causes a noticeable increase in pump pressure (5–10 atmospheres), signaling that the inner tube is ready for drilling.

6. Core Blockage Alarm System
Made up of a slidable sleeve and a disc spring, this system detects when the core or cuttings become blocked inside the inner tube or are successfully pumped to the surface. It promptly sends a signal to the surface crew, allowing for immediate action to prevent drill burn and ensure core integrity.

7.Overshot Mechanism
The overshot system includes lifting dog, overshot head, and cable swivel body. During retrieval, the overshot is lowered into the drill rod, and a cable swivel body is released to accelerate the movement. Upon reaching the core basket, the lifting dog engages the speadhead point, safely lifting the inner tube to the surface for core extraction.

8. Safety Unclamping System
In the event of resistance during core retrieval, the Safety Unclamping System plays a vital role in preventing damage. It includes a safety pin and a Locking Sleeve. If the core hook becomes stuck, the locking sleeve can be dropped from the wireline end, covering the lifting dog's tail to induce retraction, thus allowing the overshot to release from the inner tube.

Why Choose Our Wireline Double Tube Core Barrel Assembly?

• Enhanced Precision and Control – Ensures accurate core retrieval with real-time feedback.
• Durability and Longevity – Engineered with high-quality materials and reinforced components.
• Safety and Redundancy – Features multiple alarm and unclamping systems to prevent costly drill damage.
• Ease of Maintenance and Adjustment – Simplified assembly and fine-tuning capabilities for quick field servicing.
• Industry-Standard Performance – Designed to meet global drilling requirements and field conditions.