PQ Large Diameter Wireline Drill Rod for Ultra Deep Core Drilling | CGE Drilling

PQ Overshot Assembly belongs to Q series vertical hole wireline core overshot, fully manufactured in compliance with international DCDMA standards. It matches PQ wireline drill rods and double-tube inner tube assemblies, acting as the core supporting tool for large-diameter diamond wireline core drilling. It features large bearing capacity and wide gripping contact surface with the maximum core diameter in Q series. Specially designed for ultra-deep holes and projects requiring large core recovery, it is a premium mainstream drill accessory for geothermal deep wells, deep mineral exploration and large infrastructure investigation.

Application Classification
Q series overshots (BQ/NQ/HQ/PQ) are designed for vertical boreholes and downward inclined holes with an inclination of 35°~90°. QU series overshots must be used for horizontal or low-inclination tunnel boreholes of 0°~35°. The two series adopt structures for different working conditions and cannot be used interchangeably.
As the largest-size specification of Q series, the PQ overshot delivers a core diameter of 85 mm with far larger single-run core recovery and outstanding borehole stability. It fits medium-deep to ultra-deep exploration boreholes with a regular maximum working depth up to 3160 m. It is widely adopted in geothermal development, deep metal mineral exploration, large water conservancy projects and pre-investigation of tunnels that demand high core integrity and sufficient sampling volume.

The full PQ overshot consists of 12 reinforced core components from top to bottom, fully complying with DCDMA international standards and offering high interchangeability with series accessories:
1. Eye Bolt: Integrally forged thickened eye bolt connected to wireline winch. It bears ultra-large lifting load with excellent tensile and impact resistance, free from deformation or fracture under deep-hole heavy load.
2. Swivel Assembly: Equipped with heavy-duty thrust bearings and large-capacity long-life grease fittings. It rotates freely during lowering and lifting to completely avoid wireline twisting, abrasion and breakage.
3. Jar Tube & Jar Rod Assembly: Extended and thickened jarring structure with greatly enhanced jarring stroke and impact force. It efficiently releases severe tube sticking, compacted core blockage and long-term inner tube adsorption jamming in ultra-deep holes.
4. Lock Spring Sleeve & Lock Bushing: Multi-stage thickened limit locking structure keeps lifting dogs fully locked during heavy-load lifting, eliminating severe accidents such as unhooking and inner tube dropping when lifting heavy inner tube assemblies.
5. Main Compression Spring & Dog Spring: Thickened high-strength alloy springs with stable and lasting elasticity. They precisely control opening, closing and automatic reset of lifting dogs without fatigue or failure under long-term deep-hole heavy load.
6. Ball Position Indicator Mechanism: Obvious water pressure fluctuation occurs once the inner tube is fully engaged and locked. Operators on surface can quickly confirm fishing status and avoid man-hour loss caused by repeated overshot delivery in ultra-deep wells.
7. Overshot Body & Lifting Dogs: Widened and thickened double lifting dogs with greatly expanded contact area and high load limit, ensuring anti-slip and anti-unhooking performance when lifting heavy self-weight inner tubes.
8. Positioning Pins & Spring Pins: Thickened high-strength pins fix the dog assembly. Disassembly is simple, and all wearing parts can be rapidly replaced on construction sites.
9. Centralizing Guide Section: Oversized widened guide structure delivers superior centering performance inside drill rods with high coaxiality. It accurately aligns with inner tube spear head and drastically improves one-time fishing success rate in ultra-deep holes.
10. Buffer & Shock Absorption Assembly: Double-layer buffer springs plus thickened shock pads absorb huge impact force during lowering, fully protecting threads, snap rings and latch assemblies of inner tubes and reducing drill tool wear in ultra-deep drilling.

1. Wireline fishing without pulling full drill string, greatly improved construction efficiency for ultra-deep holes
After coring, only lower the overshot via wireline to grab the inner tube and extract core samples, no need to trip out the entire drill string. It drastically cuts auxiliary working hours from frequent tripping in ultra-deep wells, boosts overall drilling efficiency by over 40%, and effectively reduces shift and labor costs for deep-hole projects.
2. Special locking & gripping structure for large-bore heavy load with excellent anti-unhooking & anti-tube-dropping performance
Symmetric widened thickened double lifting dogs open rapidly under self-weight and achieve tight engagement. Matched with multi-spring self-locking system, the dogs remain locked entirely without loosening under heavy lifting load. The extended powerful jarring mechanism quickly resolves difficult downhole faults including core clogging, tube jamming and adsorption locking in ultra-deep holes, significantly lowering underground accident rate.
3. Heavy-load wear-resistant alloy material for high-intensity drilling up to 3160m ultra-deep holes
The main barrel and lifting dogs are manufactured from premium 30CrMnSiA alloy structural steel with integral medium-frequency quenching and tempering heat treatment, yield strength ≥950MPa. Lifting dogs and friction pairs are strengthened by carbonitriding surface treatment, featuring strong resistance to high-specific-gravity mud erosion and hard rock collision abrasion. Stable long-term operation is available under both clear water and mud drilling media.
4. Compliant with DCDMA international standard, universal compatibility with all brands of drilling tools
Strictly following global DCDMA wireline coring standards, it perfectly matches PQ wireline drill rods, double-tube inner tubes, latch assemblies and joints from all domestic and overseas manufacturers with high accessory interchangeability. Precise fitting tolerances guarantee smooth running without jamming inside large-diameter drill rods and excellent coaxiality, compatible with all high-torque full-hydraulic core drills for ultra-deep holes.
5. Water pressure position warning system for safe and controllable deep well construction
Standard equipped with ball pressure feedback indicator. Distinct water circuit pressure change appears once lifting dogs fully lock the inner tube, allowing operators to judge fishing results directly on rig console, reducing invalid delivery, repeated fishing and potential safety risks in deep holes.
6. Modular & standardized design for convenient disassembly and maintenance on site
All connecting parts adopt standard imperial threads without special locking tools. Wearing parts including springs, lifting dogs and bearings can be disassembled and replaced directly on site. Standardized interchangeable accessories cut inventory costs and support fast maintenance in remote mining areas and ultra-deep well construction sites.
7. Exclusive advantages of PQ maximum size, top choice for deep-hole projects requiring large core recovery
As the largest specification of Q series, PQ overshot provides an 85 mm core diameter with large single-tube core volume and complete core integrity, supporting maximum working depth up to 3160 m. It is widely used in geothermal deep well drilling, deep precious metal mineral exploration, large water conservancy survey, highway & railway tunnel geotechnical sampling, ultra-deep geological scientific research coring and other projects, serving as the preferred fishing tool for works with large core demand and ultra-deep drilling depth.