by Artur Makos, Product Manager, Exploration Products, Epiroc
The design of the traditional wireline core drilling system has remained largely unchanged since its introduction to the exploration industry. Over the years, a number of safety issues associated with the traditional wireline coring system have been addressed by manufacturers. Most of the focus has been on mitigating the risk of injury related to failures of the roll pin and the spearhead.
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, failure of the lifting dogs and failure of the spearhead to connect. Methods used by manufacturers to address these weaknesses have primarily involved incorporating twist-lock overshot locks into the traditional assembly design, as well as 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, it is the driller’s choice whether they will or will not use the safety feature. That these safety devices result in increased cycle time by adding an additional manual step presents production-focused drillers with an incentive to forego their use. The protections 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 either not always implemented by wireline coring drillers or are not utilized correctly 100 % of the time.
Furthermore, these devices are themselves subject to failure. The twist-lock overshot lock’s small parts (ball and spring) and tight clearances can lead to jamming, since small stones, sand, old grease, ice or recycled water can get in-between the parts. Retaining lanyards can fail if there is a lack of regular or proper maintenance (which would result in parts being exposed to potential damage).
When these features fail, they provide no additional measure of safety against a traditional assembly design’s risk of injury. These inherent limitations have led manufacturers to focus their efforts on safety enhancements that do not rely on a driller’s conscious, consistent and correct practice, by
incorporating the protections into the design of the wireline coring system itself.
New core barrel concept – Safety & Productivity
• No weak spear head
• No weak spring pins
• Increased lifespan for parts
• Leveraged latches – no jammed inner tubes
• Unique latch design – robust and easy to replace
• Reduced length – underground 10” (254 mm) shorter
• Quick conversion from underground to surface
• Robust spindle will resist bending during rough handling
• Loading tool for easy underground operation
The DiscovOre and Arrow 3S wireline core tooling concept shows how improvement of the common failure points in the traditional overshot and head assembly concept can 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 as well as 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 safety measure provided is automatic. It is not subject to human error or neglect. It reduces the driller’s hands-on interaction with the tooling. Furthermore, it does not add time to the coring cycle, thereby maintaining productivity, since its built-in safety is automatically engaged during connection, and is not an extra, manual step.
The biggest advantage of the Arrow 3S lies in its greater efficiency (specifically in terms of time), which is a direct result of its overshot design. The arrow-shaped body offers minimal water resistance and has a smaller cross-section area compared to other existing overshots. Drillers report that, going down the hole, the N system is approximately 15 – 20 % quicker, the H-size 25 – 35 %, and P-size 5 – 20 %.
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 Arrow 3S surface overshot would go down faster than the cable would allow when in ‘free spool’ mode, and most comment on how quickly the overshot drops.
Besides better safety and efficiency, there are many other benefits to consider when using the DiscovOre system:
• A much more rigid head assembly due to larger and therefore stronger spindle diameters and threaded connections.
• Latches that are much larger and stronger than any other system in the industry, making them more resistant to breakage and general wear. In a surface configuration, the latches are free floating and do not require a ‘lock and load’ procedure. This also allows them to wear evenly as well as last longer. The floating style, springloaded latch compensates for natural wear.
• Latches that are better supported by the latch housing (it being more than six times 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 housing is also dramatically reduced.
• Water flowing through the head is unrestricted due to maximized porting up.
• Overall, the rigid assembly functions much more smoothly in drilling mode, providing balance and low vibration, which improves core recovery.
• Solid assembly pins are used, which have eliminated spring pins or split pins that were typically used to build head assemblies. This improvement not only makes the system more rigid and reliable but also reduces the need for hammer and punch for removal or replacement of the pins. The pins are kept in the assembly by threaded bolts that can be easily unthreaded with a socket wrench, which lets the pins fall out (no punching needed at all). The hammer and punch technique is inefficient and can cause damage to the system, reducing its life and adversely affecting its function.
• There is no pivot spearhead on the DiscovOre head, as the recovery ‘point’ is on the overshot. This eliminates concerns over weak or damaged spearheads malfunctioning down the hole making recovery impossible. Damaged or weakened spearhead pivot points present dangerous conditions during lifting and lowering, which could harm operators if such failures occur out of the hole.
New Overshot concept – Speed, Safety, Simplicity
Standart overshot and Epiroc Arrow 3S
• Patented auto-lock design
• One-handed operation for easy release
• The pointed profile and deep body grooves will cut through the water for faster descent
• Short, lightweight underground overshot
• Designed to be centralized in the drill string for smoother, faster pump-in speeds
The Arrow 3S overshot design features have addressed some of the underlying issues with ‘traditional’ designs, including:
• The pivoting overshot design provides flexibility during the connection and disconnection of the inner tube assembly while out of the hole.
• A more robust design of the pivot point provides a stronger and more reliable connection, offering better safety and simplicity of function. Redundancy safety pins are still available for this design.
• Lifting dogs are protected to a greater degree and are less subject to wear during the lifting and lowering process (currently, life or wear as measured in meters drilled is reported to be three times longer than in the traditional overshot design).
The increased number of interchangeable components in both surface and underground assembly heads is welcomed, as is the resulting simplicity of converting the assembly head and overshot from surface to underground configurations. This improvement will particularly benefit drillers who drill in all directions underground and will help reduce inventory for spare parts.
Other related features include:
• The underground head assembly is the same overall length as the surface system, eliminating the need for special adapter couplings.
• Drive key design allows for more efficient and reliable underground function compared to traditional systems. We separated the function of the latch lock and head assembly rotation. The underground locking coupling has windows inside where the drive key fits to rotate the head assembly. Latches are not responsible for the rotation, but for locking the head assembly between the adapter and locking couplings.
• New drive coupling design for transfer of rotation to upper head (incorporating the drive key mentioned above). There is no longer a tang for rotating the head assembly. The drive key and windows in the locking couplings are responsible for that, eliminating latches from that function.
Drive key and drive coupling
The loading tool for underground use makes the ‘lock and load’ process a simple task (onehanded operation), provides safe handling and guarantees a proper installation of the tube assembly.
An improved propulsion seal system provides more efficient pump-in of both head and overshot assemblies. Two types of seal are used in the head assembly and overshot, working together to maintain the constant proper sealing of the space inside the rods (especially when variable wall rods are used). The DiscovOre allows you to adjust the length of the inner tube based on the same principle as in older systems, only in DiscovOre the lower latch body threads into the spindle, instead of the spindle threading into the lower latch body, as required in older systems.
The DiscovOre design allows for a larger diameter of the spindle, which is therefore stronger and less prone to bend.
Taking a holistic approach to rethinking the traditional wireline coring system, Epiroc has created a simpler, stronger and safer method that will benefit everyone.
For more information: www.epirocgroup.com