The introduction of polycrystalline diamond composites (PDC) to Hard Metals Australia’s Wombat line of hole openers and reamers can be traced back to the Western Sydney company’s first forays into Trenchless Technology in 2007.
The first hole-opener was a fixed-wing type similar to existing fabricated offerings in the market.
Though an effective and successful unit, the design presented engineering problems with axial accuracy and radial run-out of the cutter segments.
A cost issue also arose when the hole-opener was being used for different size bores at a site, or when the worn cutters had to be replaced.
The entire body had to be removed and sent to a specialised engineering facility for the cutter wings to be cut off and new ones welded on.
Looking to tackle these problems head on, Hard Metals Australia resolved to increase the rate of penetration (ROP) and reduce costs, using advanced engineering and development principles to exceed expectations.
PDC enters the scene
The first step in the evolution of the tool was to replace the fabricated cutter wings with ones that could be changed in the field.
They were fitted to a standard body, similar to imported roller cone bodies.
Additionally, the cutters were PDC rather than the tungsten carbide ones that were generally used for hole-opening and reaming through difficult strata at the time.
PDC is up to 30 times more durable than tungsten carbide but it is not as robust, making stability a key factor.
These early units were very successful in generating ROP rates and excellent bore quality on small diameters and over short distances. However, difficulties were encountered with bores over 33 cm and reaming further than 200 m.
After investigations revealed the problem centred on the wing fasteners, a stabilising ring was used to hold the wings together and improve structural stability.
The innovation was successful and in 2008 a 46 cm ream was made off a 6.75 inch pilot bore over 530 m in a single pass.
For the next two years, the design became a Trenchless Technology industry standard.
An increase in the number of blades – from three to six – produced another major advance in ROP: a 61 cm ream off a 24 cm pilot over 500 m through competent sedimentary and broken rock.
However, while this unit ticked most of the boxes, it still wasn’t easy to service in the field.
So Hard Metals Australia set about making more improvements – and the Wombat series was born.
A new beginning
The Series 1 Wombat was a development of the previous roller cone body concept, featuring a revised system for the cutter wings for greater security.
Additionally, a larger diameter central body was used for stability instead of the previous stabilising ring.
While the Series 1 had advantages in heavy duty applications on small machines with low torque and small diameter rods, the unit’s extra weight tended to make the rods “÷wind up’, causing it to whip.
The Series 3 was the next Wombat model to reach production (the Series 2 was an interim design exercise). Its major advance was to use two inline stabilisers ahead of and behind the reamer.
These allowed the body to have the sole purpose of carrying multiple cutter wings.
The unit discarded the Series 1’s excess weight, yet was more robust.
In addition to delivering excellent ROP, it was also easier to service in the field.
On one site, an extraordinary ROP of more than 30 m per hour was achieved.
The latest generation
Despite the Series 3’s advances, stabilisation was still less than ideal, making the service life of the PDC cutters suboptimal.
This gave rise to the Wombat Series 4, the culmination of the continual refinements and lessons learned from the first concept tool right through to the Series 3.
Featuring a quantum leap forward in performance, the Series 4 improved over its predecessors in several ways: near-face stability, an easily removable long body using conventional break-out jaws, large clearance paths to minimise clogging at high ROP, and forward and backward reaming capability.
The Series 4’s simple design incorporates stabilisation close to the face, making it possible to use long-life PDC cutters for strata that were previously out of the question, such as sandstone.
Further, the cutters can be disassembled and reassembled in less than an hour.
Success in the field
Since its introduction in 2012, the Wombat Series 4 has proved to be an outstanding performer.
Field trials included a 280 m bore through sandstone on the New South Wales Central Coast in 2012, a 700 m bore through sandstone and ironstone under the Hawkesbury River in 2013 and a 630 m bore through sandstone in Galston in 2015.
All of the case studies were performed using Vermeer D100 drilling rigs.
The Hawkesbury River case study was a particularly difficult project, due to large cobblestones at the entry and exit points.
Even though a casing had been installed, less durable (but less costly) tungsten carbide cutters were used for these sections, then replaced with PDC cutters for the mudstone and sandstone sections.
The cutters were replaced while the body was on the drill string in less than an hour, enabling pipe pull within two weeks of commencement.
PDC continues to evolve
The evolution of the Wombat Series disproves the long-held belief that PDC cutters are only suitable for soft sedimentary rock in trenchless drilling and boring.
Thanks to advances in stabilising PDC at the bit-rock interface, PDC is now the first choice in oilfield and gas drilling through a wide range of strata.
While PDC is less impact-resistant than conventional tungsten carbide cutters, PDC’s capacity for wear resistance can exceed that of tungsten by more than 30 times.
By creating a more stable environment at the cutting face, PDC’s excellent wear characteristics can be exploited to the great benefit of the drilling operation.
.png){kind=logo}
.jpg){kind=small}
