Polycrystalline Diamond Compact (PDC) bits have long been in existence; now they’re just becoming popular within our industry. As is usually the case when new advances emerge within an industry, big players typically fund research before it finds its way down into our hands and becomes part of everyday use – this holds true with pdc core drill bits as well.
At first, these bits were prohibitively costly because their creator companies needed their investment back. Over time though, free market forces became evident: price points became accessible while design improvements occurred simultaneously.
Although there are numerous body styles, “bullet head” style bodies seem to be most popular, pdc drill bits may also be available. However, they seem less sought-after by customers.
PDC bits differ significantly from tri-cone bits by employing thin wafers of synthetic diamond bonded to sturdy shoulders for cutting structure, providing them with different drilling mechanisms than tri-cones in terms of hardness requirements and formation type. Tri-cone bits typically drill by crushing while PDC bits either scrape or gouge the formation depending on hardness levels. Furthermore, you will note that PDC bits often feature jets while we remove jets from our tri-cones when necessary – this is deliberate; with proper pumps and jets installed, there will be an enormous pressure drop at bit face which impacts bore face impact as well as shear-thinning in order to help avoid bit balling; properly designed mud will eventually recover its original viscosity quickly enough so carry cuttings towards surface for recovery by proper design within few feet and help carry cuttings back out of formations and carry cuttings back towards surface for carrying cuttings to surface before we return again!
One of the original benefits of PDC bits was longevity; I have used several in drilling over 10,000 feet without damage being sustained to them. Of course, this depends on formation and bit design – in a sticky clay or loose sand environment, for instance, I found that “wing style” bits worked just fine while under rough running conditions they often suffered damages with whole blades ripping away! For smoother operation without chatter, “bullet head” formations tend to last longer as their smooth-running characteristics mean less chatter and usually longer maintenance requirements as wing styles used their wings more often wing style counterparts could easily do not.
One step of learning the PDC driller’s art of balling clay drilling lies in mastering how to work soft balling clay at its soft balling state, with bit rpms not really mattering as much; operators simply need to find their ideal bit speed/hole configuration combination and start drilling away! Soft clays like balling can sometimes out drill their bit; when this happens it “balls up”, torque decreases while pressure increases as this happens – due to strong electrical charges present within most clay particles that will attempt reassembling itself as quickly as it possibly can — thus leading to out drilling of this soft balling clay that once out shy once started; torque drops while pressure rises when torque drops off as pressure goes down/pressure increases due to electrical charges within these particles being disassembled upon drilling that causes this balling phenomenon known as bit ball.
First is the mud chemistry: using an effective tetraphosphate will remove charges from cuttings and allow them to stay apart instead of trying to reform again, but if only need it occasionally or twice annually Calgon dishwasher detergent works just as effectively; simply pour half a box directly in each drill pipe on connections until your desired results appear. I know I may get flak from some engineers for suggesting such unconventional remedies!
Second tactics for avoiding bit balling include adequate circulation and pressure drop at the bit. PDC bits require plenty of fluid in order to keep their bit faces clean, in addition to significant pressure drops at their mouthpiece. Therefore, run your pump as fast as you feel comfortable while maintaining an ideal pressure on your standpipe.
If you find yourself balled up anyway, pick up your bit off bottom, rotate quickly, and drink a cup of coffee – this should usually clear it. If it still won’t clear itself quickly enough, rapidly stroke pipe up and down derrick rapidly without hitting bottom! Free falling pipe can be easier on rotary table rigs than hydraulic top head rigs but will definitely assist.
Hope this helps! You should get thousands of feet of hole out of a good PDC bit, though more costly upfront, they tend to provide much lower overall costs per foot than their traditional counterparts and can usually even be rebuilt afterwards! Good luck and may your holes always turn inward!