January 20, 2018

Drilling technology

Even with new innovations in drilling tools in the down-the-hole drilling industries, nothing comes close to the penetration rate of the mature percussion-hammer technology. The harder the formation, the better these percussive products shine in comparison with other methods of drilling.

From Hughes to hammer

Howard Hughes Sr. first introduced a two-cone bit that replaced an ineffective fish-tail bit in the early 1900s.

His only son, Howard Jr., improved drilling in 1933 by announcing the three-cone (tri-cone) bit, which was widely known as the only type of drill bit that could be depended on to drill oil and gas wells.

That is, until the era of the late 1970s when inventors from TRW Mission and Ingersoll Rand raced toward a new device called a pneumatic ‘percussion hammer and bit’.

Before this, the majority of holes drilled were accomplished by ‘mud drilling’, which required the use of a water/slurry mixture to bring cuttings out of the hole.

The tri-cone bit would normally be operated at 60-80rpm and its function was to grind the rock, shale or whatever substrate it was drilling. To grind effectively, 5,000lb (2,200kg) of weight per diameter inch was required to be pulled down onto the bit.

For instance, a 9 7/8in (25cm) tri-cone would need almost 50,000lb of weight from the mast of the rig to drill at its optimum efficiency. This put enormous wear and tear on the rotary head of the drill rig and reduced its life substantially. Because of the extreme weight required, large, heavy rigs were used.

Unlike the tri-cone, a pneumatic hammer bit with a 9 7/8in-diameter head size requires only about 5,000lb of weight to allow its highest productivity. The reasoning behind this is that the bit ‘crushes’ the rock by breaking it up instead of ‘grinding’ it.

The harder the formation, the more a hammer outperforms the other methods of drilling. Drilling with percussion equipment requires a much smaller rig because only 10% of the pulldown weight is needed.

This new pneumatic hammer was operated by air directed to it via the inside of a drill pipe, thus making for a much cleaner environment. To keep dust to a minimum, the drillers soon learned to inject small amounts of water into the compressed air.

However, the huge advantage was the increase in the rate of penetration. In medium to hard formations, a tri-cone bit could be expected to drill an average of 5-10mph.

A hammer, on the other hand, would normally drill the same hole at a rate of 20-40mph. (These rates of penetration refer to general conditions.)

This penetration advantage of the pneumatic air hammer and bit contributed to the increasing popularity of this drilling method over the years.

To address the increased demand from all drilling industries (civil construction and oil and gas in particular), Drill King International has produced hammers and bits as big in diameter as 30in and 42in, respectively.

Since all drilling tools are exposed to detrimental conditions sometimes resulting in failures, the hammer bit has yet another advantage.

Most hammer-bit manufacturers, such as Drill King, have made available a retention system that will allow the driller to return a bit to the surface even if it has broken in the hole. This has proven to be a valuable tool for all drilling industries.

When another type of bit breaks in the hole (something all drillers are destined to experience if they drill long enough), conventional methods of retrieving the broken bit include trying to screw an ‘overshot’ threaded pipe over the broken part, pushing a hard metal spear with threads into the steel, or sending a magnet down the hole in an attempt to save the hole. These retrieval methods are all risky and often unsuccessful.

New technology

By the late 1980s, percussion hammers had taken roughly 50% of the drilling industry away from the tri-cones. That number continued to grow right up to the 21st century, with hammers being used in approximately 75% of oil-and-gas drilling compared with 25% being drilled by tri-cones.

The past decade has brought with it new technologies, including polycrystalline diamond compact (PDC) bits. These drag bits have cutters on them made from synthetic diamonds. They have been effective in shale, especially when a deep hole is required, because they wear extremely slowly.

That being said, the PDC still only maintains penetration rates of 25-35ft per hour in contrast to a hammer’s rate of 120-200ft per hour in shale, making pneumatic (percussion) hammers the most resourceful product.

Immediately behind the PDC cutters came the diamond-enhanced dome carbide that could be used in both tri-cones and hammer bits.

In virtually every application, this new diamond-impregnated tungsten carbide would show no wear even after the steel matrix of the bit showed extended wear characteristics and fatigue.

The gauge size, which is very important in maintaining the integrity of the hole size for casing, stayed consistent from the top of the hole all the way to the total depth. This discovery positively altered the market for percussion drilling.

Suddenly, a hole could be drilled several thousand metres without having to ‘trip’ out of the hole to replace a bit. As drilling depths have increased throughout the past years, operators have found that major savings are the result.

Pneumatic hammer-drilling technology has been undergoing major developments in the last decade in the form of overburden drilling systems and water-propelled hammers.

Drill King International has stayed on top of these innovations with its DK Casing Advance System for up to 24in OD casing and its latest ‘WAI’ hammer, which utilises high-pressure water to power the hammer drilling and bring the cuttings out of the hole. One thing is for sure: the future holds substantial advancements for percussion-hammer drilling technology.

Drilling is helpful in mining and construction, among other projects.


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