The design of the traditional wireline core drilling system had in large part remained unchanged since its introduction to the exploration industry. A number of safety issues associated with the traditional wireline coring system have been addressed by manufacturers over the years. Most of the focus has been on mitigating risk of injury associated with failures of the roll pin and the spearhead associated with traditional wireline coring assembly designs.
Failures of the roll pin and spearhead are not limited to worn or damaged tools but have occurred even with new tooling. They include loss or failure of the roll pin, catastrophic failure of the lifting dogs and failure of the spearhead to connect. Methods used by manufacturers to address these failures have primarily involved incorporating twist-lock overshot locks into the traditional assembly design and the use of retaining lanyards.
Both of these strategies, however, rely on the wireline coring driller’s conscious, correct and consistent use of the safety feature. Yet they allow drillers to elect when they will or will not use the safety feature. That these safety devices result in increased cycle time by adding and additional manual step presents production-focused drillers an incentive to forego their use. The safety that these features offer can also become compromised through driller error during careless moments induced by fatigue or distraction. In actual practice, then, the safety features are not utilized by the wireline coring drillers, or are not utilized correctly, 100 percent of the time.
Furthermore, these devices are themselves subject to failure. The twist-lock overshot lock’s small parts and tight clearances can lead to jamming. Retaining lanyards can fail. When these features fail, they provide no additional measure of safety against over a traditional assembly design’s risk of injury.
These inherent limitations have focused manufacturer efforts on incorporating safety enhancements into the design of the wireline coring system itself that do not rely on a driller’s conscious, consistent and correct use.
The DiscovOre & Arrow 3S wireline core tooling concept featured in this presentation shows how one manufacturer improvements upon common failure points of the traditional overshot and head assembly concept increase safety by making it an intrinsic part of how the components connect. The design employs automatically locking lifting dogs. It eliminates the roll pin altogether, and it eliminates failures associated with the traditional spearhead design, which the lanyard system was designed to protect against in other wireline coring systems.
Most importantly, the additional measure of safety it provides is automatic. It’s not subject to human error or deliberate neglect. It reduces the driller’s hands-on interaction with the tooling. Furthermore, it does not add time to the coring cycle, preserving productivity, since its built-in safety is automatically engaged during connection, not as an extra, manual step.
The biggest advantage for more efficient (time related) function is in the overshot design. Drillers report that the N system is approximately 15-20% quicker going down the hole, 20-25% quicker when using H size system and 30-35% quicker when using P size. Note that the H system uses the regular N size overshot for recovery and P size ads only cross centralizer, so the displacement area of the larger H or P drill rod will facilitate increase in descent speed.
Of course, the speed and efficiency of the wireline cable as it spools off of the winch drum will have a big effect on the drop speed. Some drillers have reported that the Discovore surface overshot would go down faster than the cable will let it when in “free spool” mode, and most comment on how quickly the overshot drops.
There are many other positives to consider when using the Discovore system:
The head assembly is much more rigid due to larger spindle diameters and threaded connections.
The latches are much larger and stronger than Excore ( and most others in the industry) which makes them more resistant to breakage and general wear. In surface configuration, the latches are free floating and do not require “lock and load” procedure. This also allows the latches to wear evenly and last longer. The natural wear is compensated for by the floating style spring loaded latch.
The latches are better supported by the latch housing by more than 6x the contact area. This stabilization reduces latch wear and allows for much improved driving support for the latch when rotating the drill string”. Damage to the latch housing is also dramatically reduced.
Water flow through the head is unrestricted due to maximized porting up to the landing indicator bushing ( the landing indicator bushing is the smallest restriction in the flow system), we use the same indicator bushing that is currently in the Excore system.
The overall rigid assembly functions much more smoothly in drilling mode providing balance and low vibration which improves core recovery.
The Discovore uses solid assembly pins which have eliminated spring pins/split pins that were typically used to assemble head assemblies (latches, latch case, spearheads etc.) This improvement not only makes the system more rigid and reliable but reduces the need for hammer and punch for removal/replacement. Hammer and punch is not only inefficient but can also cause damage to the system, reducing life and affecting function of the system.
There is no pivot spearhead on the Discovore head, the recovery “point” is on the overshot. This eliminates concerns over weak or damaged spearheads malfunctioning down the hole making recovery impossible, also Damaged or Weakened spearhead pivot points presented dangerous conditions during lifting and lowering which could harm operators if such failures occurred out of the hole.
The overshot design features have addressed some of the underlying issues with “traditional” overshot designs:
Pivoting overshot design provides flexibility during connect and disconnect of inner tube assembly while out of the hole
Much more robust design of the pivot point provides a stronger and more reliable connection providing better safety and simplicity of function. Redundancy safety pins are still available for this design.
Lifting dogs are protected to a higher degree and are less subject to wear during lifting/lowering process ( currently we have reported life/wear measured in meters drilled being 3 times longer than traditional overshot design)
Some other features such as more common components between surface and underground heads are noted as well as simplicity to convert surface to UG.
The underground head assembly is the same overall length as the surface system so no need for special adapter couplings.
The drive key design for more efficient and reliable underground function over traditional systems.
New drive coupling design for transfer of rotation to upper head (incorporating drive key mentioned above)
A loading tool for underground use makes “lock and load” process a simple task, a one handed operation. Provides safe handling and guaranteed proper installation of the tube assembly.
Improved propulsion seal system provides more efficient pump-in of both head and overshot assemblies.