Horn Bore Milling and Thread Milling Raises Productivity and Quality for Oil Industry Supplier

Weatherford International Ltd is a leading multi-national developer and supplier of advanced oil and gas well drilling solutions. Operating out of their Arbroath facility they recently implemented a Continuous Improvement exercise on one of their main components. Within this component are “Port details” used to feed drilling fluid and lining ‘cement’ to the drilling area. Depending on the bore diameter of each well, between 3 and 18 of these ports are required to be machined per drilling head assembly.

The port details were previously machined using a multiple insert form tool followed by a single point thread milling tool.  Horn, in conjunction with Weatherford, initially ran “Cutting Trials” to develop a new method based on helical milling and estimate likely cost savings. Results proved 15 minutes per port detail can be saved with the new method as the 20 minute cycle previously required has reduced to 5/6 minutes; this equates to a machining time saving ranging from 45 minutes to 4.5 hours per head. In addition, the Horn tooling package, which comprises a Type 628.0400.00 AS45 milling cutter and a Type 628.1525.01 TI25 thread milling cutter, provides superior finish, profile accuracy and tool life.

The type of well tooling on which the Horn tooling is utilised is called ‘drilling with casing’ (DWC) and is one amongst a number of major products produced at Arbroath.   Weatherford has offered DWC technology for several years.  ‘Conventional’ drilling uses a drill bit to drill the well but it and its driving pipework subsequently needs to be retrieved prior to insertion of a casing string. DWC uses the casing pipe that drives the cutting system to line the well as it goes.

The system uses a ‘sacrificial’ boring head.  This incorporates fluid distribution nozzles that continually fill and clean the annular void between the pipe and the bore hole as the well advances deeper and deeper.  Upon reaching target depth cement is pumped through the nozzles to fill the annular void, securing the casing in place. These nozzles are located in the detailing produced using the Horn tooling. 

Grant Robb, the Weatherford production engineer explains.  “The nozzles are a standard fitting but they vary in number according to the diameter of the drill head.  This can be as large as 27 inches – with 12-18 ports - or as small as 5 inches with 3 ports.  Although the form tool produced the feature with acceptable accuracy we were conscious of the fact that cutting speeds could not be optimised due to the variation in diameter.  Additionally, periodic indexation and replacement of the inserts was necessary.  Likewise the single point threading bar was relatively old technology that necessitated occasional rework.”

Weatherfield asked Horn to propose an alternative solution, based on earlier success with other tool packages.  The proposal offered was to begin by drilling a 30 mm through-hole as previously, but to produce the internal form by helical interpolation to drop mill the profile using the Type 628 six tooth milling cutter. The bore diameter is 38.5mm at the top, tapering to 36mm for the section that is later to be threaded, then tapering to 35mm, then stepping down to 30mm for the final section.  Cutting data for the drop milling operation is Speed 10,000 rev/min, Feed 4000mm/min.

Once the internal profile is completed the Type 628 thread mill produces a 1.5 inch diameter, 12 pitch UNF thread in the top section, machining at 10,000 rev/min with feed at 4000mm/min.  In both cases the insert is mounted on a Horn M328.0020.10A holder.

 “It has been a very successful project.” Mr Robb confirmed.  “Right from the first test it was obvious that the productivity, finish and comparative cost using the Horn tooling was a significant improvement over what we were used to.  Since then we’ve completed around 50 of the distribution heads with no discernible wear on the tools but we have larger quantities coming along later in 2013.  The port boring operation accounts for up to 15 per cent of the machining time for these parts so the overall productivity improvement is well worthwhile.”