BQ Wireline Core Drill Rod DCDMA Standard for Shallow Mineral Exploration | CGE Drilling

BQ Overshot Assembly is a vertical hole wireline core overshot of Q series. Manufactured in compliance with international DCDMA standards, it is matched with BQ wireline drill rods and double-tube inner tube assemblies, acting as the core auxiliary tool for diamond wireline core drilling.
Application Classification
Q series overshots (BQ/NQ/HQ/PQ) are specially designed for vertical holes and downward inclined boreholes with an inclination of 35°~90°. For horizontal or low-inclination tunnel boreholes ranging from 0° to 35°, QU series overshots shall be adopted instead. The two series cannot be used interchangeably.
As the small-size specification in Q series, the BQ overshot delivers a core diameter of 36.5 mm. It is suitable for shallow to medium-depth exploration boreholes with a maximum working depth up to 1200 meters.

The complete BQ overshot consists of 12 core components from top to bottom:
1. Eye Bolt: Connects the wireline winch and bears the lifting load.
2.Swivel Assembly: Equipped with thrust bearings and grease fittings, it allows free rotation during lowering and lifting to prevent wireline twisting.
3. Jar Tube & Jar Rod: Provides up and down jarring force to release stuck inner tube assemblies.
4. Lock Spring Sleeve & Lock Bushing: Locks the lifting dogs to prevent accidental unhooking during operation.
5. Main Compression Spring & Dog Spring: Controls the opening, closing and resetting of the lifting dogs.
6. Ball Position Indicator Mechanism: Generates pressure feedback once the inner tube is fully caught, allowing operators on the surface to confirm successful latching.
7. Overshot Body & Lifting Dogs: The core gripping parts that firmly engage the spear head of the inner tube assembly.
8. Positioning Pins & Spring Pins: Secure the dog structure, enabling easy disassembly and convenient maintenance.
9. Centralizing Guide Section: Automatically centers the overshot inside the drill rod for precise alignment with the inner tube spear head.
10. Buffer & Shock Absorption Assembly: Reduces impact force during lowering, protecting threads and snap rings of the inner tube assembly.

1. High-efficiency Fishing Without Drill Rod Pulling
After coring completion, the overshot is lowered simply by wireline to grab and retrieve the inner tube assembly directly inside the drill rod. It is unnecessary to pull out the entire drill rod string, which greatly reduces auxiliary tripping time and improves deep-hole drilling efficiency by more than 40%.
2. Special Stable Gripping Structure for Vertical Holes
Adopts double-sided thickened lifting dogs with symmetrical stress distribution. When descending in vertical holes, the dogs open rapidly by self-weight and firmly engage the spear head. The multi-spring self-locking structure keeps the dogs fully locked during lifting without unhooking, effectively preventing inner tube dropping accidents. Built-in jarring mechanism enables up-and-down jarring movement to loosen stuck inner tubes or blocked cores and reduce downhole failure risks.
3. High-strength Wear-resistant Material & Long Service Life
The main barrel and lifting dogs are made of high-quality 30CrMnSiA alloy structural steel with integral medium-frequency quenching and tempering treatment, achieving a yield strength of ≥950MPa. Key gripping parts and friction pairs undergo carbonitriding treatment for excellent resistance to mud erosion and rock collision. It is compatible with both clear water and mud drilling media.
4. DCDMA International Standard & Strong Versatility
Fully compliant with the global universal BQ wireline coring tool system, it adapts to BQ drill rods, inner tube assemblies and latch assemblies from various manufacturers with high interchangeability. Precise internal and external fitting tolerance ensures smooth running, no jamming and high coaxiality.
5. Position Feedback Design for Safe & Controllable Operation
Equipped with a built-in ball pressure indicator. After successfully latching the inner tube, the water circuit pressure changes obviously, allowing operators to directly judge the fishing status on the rig console, avoiding empty fishing and misoperation and reducing rework frequency.
6. Easy Maintenance & Standardized Wearing Parts
All connecting parts adopt standard imperial threads. Wearing parts such as springs, lifting dogs and bearings can be disassembled and replaced without special tools. Universal interchangeable accessories lower inventory costs and support rapid on-site maintenance in field operations.
7. Exclusive Advantages for Small-bore Holes (BQ Special)
As the smallest-bore specification in the Q series, the BQ overshot features a slim barrel and optimized guide section. It produces low running resistance inside small-size drill rods and avoids scratching the inner wall. It is widely applicable for small-bore exploration projects including mineral reconnaissance, shallow hydrological holes, engineering geological investigation and soil sampling.